A blank black page. A circular seal with Latin text "UNIVERSITAS CALIFORNIAE" around the top edge, and "MDCCLXIV" at the bottom center. Below the seal, the text "EX LIBRIS" is written. This is a placeholder for a bookplate. The text "EX LIBRIS" is typically used to indicate that this book belongs to someone named "Ex Libris". The design often includes a seal or crest, which may represent the institution or organization associated with the owner. A blank page with a light gray background. Blank white sheet of paper. 1 A blank, light yellow page with a subtle texture. ASTRONOMY A blank page with a light beige background. 2 Saturn illustration THE PLANET SATURN November 28, 2001 16 # ASTRONOMY BY GEORGE F. CHAMBERS, F.R.A.S. Of the Inner Temple, Barrister-at-Law AUTHOR OF "A HANDBOOK OF ASTRONOMY," "THE STORY OF THE COMETS," AND OTHER WORKS WITH 550 ILLUSTRATIONS, INCLUDING 8 COLOURED PLATES A circular medallion with a portrait of a man's profile on the left side and a date "1876" on the right side. Gold Medal of the Royal Astronomical Society NEW YORK D. VAN NOstrand COMPANY TWENTY-FIVE PARK PLACE QB44 C5 PRINTED IN GREAT BRITAIN TO VIMU AMOROSSILIO PREFACE. This volume is not a formal treatise on Astronomy, nor is it a mere educational textbook; but the idea which underlies it may be realised from the following considerations. An extended experience as an astronomical writer, and likewise lecturer on the science, coupled with much intercommunica- tion with astronomers at home and abroad, has led me to notice the remarkable spread of late years all over the world of a taste for Astronomy. Some recent eclipses of the Sun have been attended by crowds of people, a great deal to do with this, especially Halley's Comet of 1769. I have often been struck by the frequent requests for informa- tion on astronomical topics from all sorts of people, the majority of whom are far from being scientifically educated that they should sit down and seriously study text-books on the subject. These are the people whom I want to get hold of through this volume. There is nothing profound or inconveniently deep in it, but it just gives a popular outline of leading facts, which may be easily grasped by any fairly educated person who is only interested in astronomy. It is written for those who have thought to the matter, but who may happen to possess a small telescope of, say, two or three inches aperture, or even a good opera-glass. My endeavour has been to deal descrip- 285716 vi PREFACE. tively with some of the more ordinary sights of the Heavens, the examination of many of which can be carried out with the class of instrument just mentioned. Mathematical and theoretical matters and speculations have been kept entirely in the background. It will appear, I hope, from the foregoing statement that my idea has been to direct the reader's attention to what may be called the "outer" side of astronomy, and to furnish information on such phenomena as are constantly brought under the notice of people in general without exactly being sought for by them. I want the reader to be able to answer such questions as "What is the Sun?" "What is the Moon?" "What is the name of that bright star, or is it a planet, which I see in the west every evening?" "Is there any other star like our own Sun?" "Is there any other light of the Moon?" "Was Sir George Cornwall Lewis right when he stigmatised Astronomy as a science of 'pure curiosity'?" Notions such as these, and others much more shallow, have often been addressed to me, and I want to provide people who possess only a smattering of scientific knowledge with the means of answering some of these questions which frequently arise in conversation. The following are some events or discovery ways mentioned in the newspapers or talked about. It will be seen, I think, that whilst my aims are mainly to make known how to provide material for sensible and exact knowledge, truthfulness and correctness are needing too severe a demand on the time or mental powers of those who patronise the book. The facts contained in this work are obtained from many sources, and whilst it may be said of some of them that they are not new, or only reproduce old ideas in new form, yet I have endeavoured as far as possible to be chary in the insertion PREFACE. vii of such, being desirous of providing my readers with pictures which are not in general circulation or accessible to the reading public. This really means that I have ransacked the publications of various scientific societies, European and American, for illustrations. America has been a rich field for me. I have to thank Mr. H. F. Bushell, of the Gresham School, Holt, Norfolk, for kindly reading the proof-sheets, but my special thanks are due to Mr. J. W. Bower, who has drawn by name, who have provided me with drawings and photographs, without which it would have been impossible to produce this, the most copiously illustrated book on Astronomy ever published in England. There are, however, a few names which stand out more conspicuously than others, and which must receive special mention. In such a list as this I follow the following : Pro- fessor E. W. Bate of the Yerkes Observatory, Williams- town ; Professor W. H. Pickering, of the Harvard College Observatory, an institution to which Astronomy owes more than any other branch of science ; Sir James Croll, Astrono- mical Society and of the British Astronomical Association ; and several private friends, under which head there must be included Mr. E. M. Antoniadi, Mr. E. H. Barlow, Mr. S. Bolton, Rev. J. B. Boulton, Mr. A. C. Brown, Mr. J. R. Gifford, Mr. F. W. Longbottom, Admiral Moore, Rev. T. E. R. Phillips, Mr. W. E. Wilson, Mr. H. E. Wood, together with Messrs. Cooke & Sons and Sir H. Grubb. A page from a book with text and images. An attentive, or even a cursory, perusal of this book will give the go-by to the idea that astronomy is a science of " pure curiosity". On the contrary, it has a great deal to recommend it, not only as a science, but also as a means of improving our daily life, and of making us more happy and contented in our daily existence. But over and above all this it is a science which is so manifestly connected with the Divine Hand which controls everything around us, that we cannot mistakeably call the Universe having been created, and being still maintained, by a Divine Hand which controls everybody and everything. It is this connection with the Divine Hand which inspired Young in his *Night Thoughts* to write the significant words "An undevout astronomer is mad." G. F. C. Letham Grange, Sydenham. viii CONTENTS. Preface . . . . . . . . . . . . pp. v-vii Contents . . . . . . . . . . . ix-xiv List of Illustrations . . . . xv-xxiii The Greek Alphabet . . . . xlv CHAPTER I. INTRODUCTION. The scope of the Science of Astronomy.--Its modern development.--The ancient science of astronomy.--The importance of keeping the treatment of the science within defined limits.--The different divisions of the subject.--The relation of astronomy to other sciences.--Chap. I. "Astronomy without Mathematics."--Theoretical Aspects of Astronomy.--Theoretical astronomy.--Theoretical astronomy and the practical astronomer.--Amateurs may distance with knowledge of mathematics altogether and of the theory of eclipses and q's in part.--The modern application of the spectroscopy. PP. 1-4 CHAPTER II. THE SUN. Important position occupied by the Sun.--Its general appearance.--Its magnitude and distance from us.--The apparent motion of the Sun.--Spots on the Sun's surface periodically.--General description of them.--Periodicity of sunspots.--Distribution of spots in latitude.--Discovery of the periodicity of sunspots.--Sunspots and solar eclipses.--Sunspots and auroras.--Sunspots and weather.--Possible influence of some of the planets on Sun-spots.--Ways in which we can study the Sun.--Asymmetry of the Sun.--Asymmetrical movements at spots at different seasons of the year.--Noble large spots.--Light-and-heal-giving powers of the Sun.--The "Fate" universe. IX pp. 5-23 X CONTENTS. CHAPTER III. THE MOON. Next after the Sun in popular interest—How soon visible after being new.—Its phases.—Its movement through the heavens.—General physical aspects of the Moon.—The lunar day and night.—The lunar tides and chains.—Isolated peaks.—Signs of volcanic action.—Resemblance be- tween the Moon and the Earth.—The Moon's appearance from different mountains.—The so-called seas on the Moon.—General appearance of the Moon from the Earth.—The Moon's phases and their causes. The motions of the Moon very complex.—The Librations.—The Harveled Moon.—The Phases of the Moon.—The Phases of the Moon seen from the Earth. Sun.—Supposed influence of the Moon on the weather.—Other influences of the Moon upon terrestrial phenomena. Influence of the Moon on clouds.—Influence of Moonlight on human being, a fable. 28-30 CHAPTER IV. THE TIDES. The tides matter of interest to the inhabitants of maritime countries. —Importance of tidal phenomena in navigation and commerce. —that the Moon greatly preponderates.—Spring Tides—Neap Tides. —the tides are caused by the attraction of the Sun and Moon upon the Earth. —"Pruning" and "lagging" of the tides—Equinoctial tides—Tides at the equator—Tides at the poles—Tides in the Atlantic Ocean—Tides in Great Britain—Amongst the South Sea Islands—Influence of the baro- meters.—Journey of the tidal waves round the Earth—"The" Book. PP. 47-54 CHAPTER V. THE PLANETS GENERALLY. What the planets are.—May be conveniently divided into two groups— "The Interior Planets"—Mercury, Venus, Earth, Mars. —"The Exterior Planets" Certain Planets have satellites.—The purpose served by them—Certain Planets have no satellites—Their orbits are elliptical—Orbits in Opposition—Transits across the Sun—Characteristics common to all the planets—Characteristics peculiar to each planet—The Sun's position in Herakles' statement—Connection of two Planets—Instances of this— Trans-Neptunian planets. 55-66 CONTENTS. xi CHAPTER VI. THE MOST INTERESTING AND FAMILIAR PLANETS. A classification of the planets—Mercury—Difficult to observe—Sun's influence on its motions—Venus—The phases of Venus—Its characteristics—How to find Mercury or Venus—Mars—Movements resembling those of the Earth—Jupiter—Saturn—The rings of Saturn—Uranus—Neptune—Pluto—The dwarf planets—Alleged satellites—Phases—Galileo's anagram.—Statistics. Mercury is the nearest planet to the Sun. It is very small, and subject to a slight phase. This planet very accessible for observation. The Sun's light is so strong that it is difficult to see it at all times. The phases of this planet are similar to those of the Moon. Polar snows—Spots—Markings very permanent.—Its colour, white, like that of the Moon. The Sun's light is so strong that it is difficult to see it at all times. The phases of this planet are similar to those of the Moon. Polar snows—Spots—Markings very permanent.—Its colour, white, like that of the Moon. Venus—the most beautiful planet—The phases of Venus—The colours of Venus—The atmosphere of Venus—The clouds of Venus—The atmosphere of Venus—The clouds of Venus. Mars—the red planet—The phases of Mars—The colours of Mars—The atmosphere of Mars—The clouds of Mars. Jupiter—the largest planet—the four Galilean moons—the Great Red Spot—the Great White Spot—the Great Black Spot—the Great White Spot—the Great Black Spot. Saturn—the most beautiful planet—the rings of Saturn—the rings of Saturn. Uranus—a blue planet—the rings of Uranus—the rings of Uranus. Neptune—a blue planet—the rings of Neptune—the rings of Neptune. Pluto—a small planet—a dwarf planet—a satellite—a moon—a dwarf planet—a satellite—a moon. Statistics. CHAPTER VII. THE LESS KNOWN PLANETS. The planets of this chapter of little interest to the amateur.—History of the discovery of the planets.—The discovery of Uranus by William Herschel.—The discovery of Neptune by Leverrier and Adams.—The discovery of Pluto by Clyde Tombaugh.—Summary respecting their orbits. CHAPTER VIII. ECLIPSES. The principles of eclipses—Other kinds of phenomena.—Two anomalous phenomena—the difference between eclipsions of the Sun and the Moon.—Total eclipse and partial eclipse.—The cause of eclipsions.—The method used in observing the Solar Eclipse of the Sun considered.—The accompaniments of an eclipse.—The appearance during an eclipse.—The terror of savages.—Inferences of this.—The darkness.—The fall of temperature. pp. 58-113 xii. CONTENTS. two.---The red flames.--Bally's Bands.--The Corona.--Details relating thereto.--The Moon's shadow.--Shadow-bands.--Brushes of light.--The Corona.--The Sun's rays.--The Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--the Sun's rays--173-174 CHAPTER XI. COMETS. Always objects of popular interest.--Very numerous.--Telescopic comets. Great comets visible to the naked eye.--Great changes in the appearance of comets.--Comets of the 18th century.--Comets of the 19th century. Unusual changes exhibited by a telescopic comet.--Become visible as they appear in the heavens.--Disappear after a short time.--Why do some comets have tails and not others?—Those quantities difficult of explanation.--The tail of a comet.--The tail of a comet.--The tail probably cylindrical.--Brahmanen’s theory of tails.--The Light-pressure theory of tails.--Orbits of comets.--Periodical comets.--Calendrical comets.--Some facts about comets. CHAPTER XII. SHOOTING-STARS. Various classes of luminous meteors.--Shooting-stars.--Fireballs. Aurorae.--Radiant points of shooting-stars.--Account of the most remarkable shooting-stars.--Shooting-stars in the northern hemisphere.--Hundredal illusions. Celebrated great showers.---Fireballs.---Shooting-stars in the southern hemisphere.---Shooting-stars by W.H. and Brookes.---Their sizes, distances, and movements.---Comparative size of shooting-stars and comets.---Shooting-stars and comets.---Shooting-stars, stars, fireballs, and aurorae all of the same nature.---Circumstances attending the fall of shooting-stars. CHAPTER XI. THE STARS. The apparent movement of the stars on a starlight night.--The stars in the sky are not fixed in their places but move with respect to one another. The stars visible vary with the latitude.---The expression "fixed stars,"---
Contents
Two. The red flames.—Bally’s Bands.—The Corona.—Details relating thereto.—The Moon’s shadow.—Shadow-bands.—Brushes of light.—The Corona.—The sun’s ray.
The sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray—the sun’s ray-the moon.
The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona.—The corona—173-174
Chapter XI. Comets.
Always objects of popular interest.-Very numerous.-Telescopic comets.
Great comets visible to the naked eye.-Great changes in the appearance of comets.-Comets of the 18th century.-Comets of the 19th century.
Unusual changes exhibited by a telescopic comet.-Become visible as they appear in the heavens.-Disappear after a short time.-Why do some comets have tails and not others?-Those quantities difficult of explanation.-The tail of a comet.-175-176-177-178-179-180-181-182-183-184-185-186-187-188-189-190-191-192-193-194-195-196-197-198-199-200-201-202-203-204-205-206-207-208-209





















































































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Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Celestial Comets.
Chapter XII.
Shooting-Stars.
Various classes of luminous meteors.
Shooting-stars.
Fireballs.
Aurorae.
Radiant points of shooting-stars.
Account of the most remarkable shooting-stars.
Hundredal illusions. Celebrated great showers.
Fireballs.
Shooting-stars in the northern hemisphere.
Hundredal illusions. Celeb
Chapter XI.
Stars.
Apparent movement of the stars on a starlight night.
Stars in the sky are not fixed in their places but move with respect to one another.
Stars visible vary with the latitude.
Expression "fixed stars,"--- pp. 137–843 CHAPTER XII. GROUPS OF STARS AND NEBULAS. Stars in groups classified.—Irregular groups.—Clusters of stars more or less compressed.—Nebulae.—Classification of nebulae.—Annual nebulae.—Planetary nebulae.—Nebulae of the first magnitude. Nebulous stars.—Large nebulae of irregular form.—Exemplification of the subject of this chapter by the "Milky Way." —the Milky Way.—Brief description of its position.—Its historic names. pp. 246–843 CHAPTER XIII. THE CONSTELLATIONS. The subject of great interest.—The best way of learning their posi- tions.—The effects of the distant movement.—Star-atlases and plani- pherographs.—The constellations in the northern hemisphere at the sixth magnitude.—Standard stars of the first magnitude.—Alignment of the stars with respect to the pole-star and sun.—A star atlas for the survey of the Northern Hemisphere. pp. 244–255 CHAPTER XIV. TELESCOPES. Telescopes are two in kind. —Reflectors, Reflectors. Various kinds of reflectors. The reflecting telescope. A curved mirror. The plane mirror. Aberration—Chromatic aberration. The opera glass. Standards for tele- scopes. The refracting telescope. The achromatic telescope. The equatorial mounting.—Accessories to a telescope.—Driving-clock. Secondary mirrors. The Newtonian telescope. The Cassegrainian tele- scope. The Gregorian telescope. The Herschelian telescope. The refractor for astronomical purposes. Accessories to a refractor. Description of how to build one. pp. 256–282 xiv CONTENTS. CHAPTER XV. TIME AND ITS MEASUREMENT. Years.—Months.—Weeks.—Days.—Hours.—The Sidereal Year.—The Mean Solar Year.—The Nauticalal Year.—Hipparchus.—The Calendar until the 17th Century A.D.—The Gregorian Calendar—XIII.—His Calendar adopted by England—but not by Russia.—Old calendars—From the 18th Century onward—From Laplace.—Savages took time by “Moon”.—Divisions of the Day, Night, and Year—Meridian.—Greenwich chosen for this.—Standard time—Usage of the 12th hour—The 24 hours of the day—How to use it for obtaining the time. pp. 230–309 CHAPTER XVI. THE SPECTROSCOPE ASTRONOMICALLY. What is a spectrum?—The decomposition of sunlight.—Brief history of the spectroscope—Sir William Herschel’s discovery—J. C. Fraunhofer—J. J. Thomson—F. W. Huggins—J. D. Lambert—J. B. D’Arrest—J. L. Foucault—J. L. Foucault’s star-plotter—as ascertained by the spectroscope. pp. 309–359 CHAPTER XVII. TABLE OF THE CONSTELLATIONS, WITH A BRIEF DESCRIPTIVE ACCOUNT OF EACH. pp. 310–382 APPENDIX I. STATISTICS RESPECTING THE PLANETS AND THEIR SATELLITES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . pp. 323–334 APPENDIX II. CATALOGUE OF CELESTIAL OBJECTS EASY FOR SMALL TELESCOPES. . . . . . . . . . . . . . . . . . pp. 347–368 Index. pp. 359–365
LIST OF ILLUSTRATIONS.
10. The PLANET SATURN (Bolton). Plate 1 FromJupiter
1008 Mars (Bolton) PLATE XXXVII
108 Jupiter (Bolton) XXXIX
141, 142 PROMENANCES ON THE SUN XXVIII T14
236 The Great Moon (Tempe) LXXXVII
258 DAYLIGHT METEOR (J. Narwyl) LXXXIII
265 COLOURED STARS LXXXIV 208
265 COLOURED STARS LXXXV 240
BLACK-AND-WHITE ILLUSTRATIONS.
2.East Indian CoralS.8
IIbIIbIIbIIbIIb
NumberDescriptionDatePage No.Description
1.A Typical Sun-spot (F. Langley)Oct. 22, 1863I12
4.A Typical Sun-spot (F. Langley)Oct. 22, 1863I12
7.A Typical Sun-spot, showing Spots, July 31, 1905 (Barlow)III124
9.A Typical Sun-spot, showing Spots, July 31, 1905 (Barlow)III124
7.A Typical Sun-spot, showing Spots, Feb. 7, 1907 (Barlow)II124
9.A Typical Sun-spot, showing Spots, May 6, 1907 (Barlow)VII124
7.A Typical Sun-spot, showing Spots, July 25, 1907 (Barlow)
9.A Typical Sun-spot, showing Spots, May 4, 1907 (Barlow)IIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIbIIb13 VI 14 VII 14 VIII 15 IX 19 X 22 XI 23 XII 24 XIV 26 XV 26 XVI 26 XXI 34 XXII 34 XXIII 35 XXIV 36 XXV 37 XXVI 37 XXVII 37 XXVIII 37 XXIX 37 XXX 37 XXXI 37 XXXII 37 XXXIII 37 XXXIV 37 XXXV 37 XXXVI 37 XXXVII 37 XXXVIII 37 XXXIX 37 XLX 37 XLXI 37 XLII 37 XLIII 37 XLIV 37 XXVIi VIII - I5 XXVII VIII - I5 XXVIII XII - I5 XXIX XIV - I5 XXX XVI - I5 XXXI XVII - I5 XXXII XVIII - I5 XXXIII XIX - I5 XXXIV XII - I5 XXXV XIV - I5 XXXVI XV - I5 XXXVII XVI - I5 XXXVIII XVII - I5 XXXIX XVIII - I5 XLX XIX - I5 XLXI XII - I5 XLII XIV - I5 XLIII XV - I5 XLIV XVI - I5 XXXXI XVII - I5 XXXXII XVIII - I5 XXXXIII XIX - I5 XXXXIV XII - I5 XXXXV XIV - I5 XXXXVI XV - I5 XXXXVII XVI - I5 XXXXVIII XVII - I5 XXXXIX XVIII - I5 XLX XIX - I5 XLXI XII - I5 XLII XIV - I5 XLIII XV - I5 XLIV XVI - I5 XXXXVIi VIII - II0 XXXXVii VIII - II0 XXXXViIi VIII - II0 XXXXVIii VIII - II0 XXXXViii VIII - II0 XXXXViix VIII - II0 XXXXViixi VIII - II0 XXXXViixii VIII - II0 XXXXViixiii VIII - II0 XXXXViixiv VIII - II0 XXXXViixv VIII - II0
LIST OF ILLUSTRATIONS.
No.The Great Sun-spot of 1865 disappearing on Nov. 3 (Hendel)
106.The Great Sun-spot, Oct. 20, 1865 (Bar-
117.Gravitation and Fascia, Nov. 16, 1865 ( |
No.Description of Illustration(s)
No.The Great Sun-spot of 1865 disappearing on Nov. 3 (Hendel)
PLATE PAGE V V- III V- IV V- VI V- VII V- VIII V- IX V- X V- XI V- XII V- XIII V- XIV V- XV V- XVI V- XVII V- XVIII V- XIX V- XXI V- XXII V- XXIII V- XXIV V- XXV V- XXVI V- XXVII V- XXVIII V- XXIX V- XXXI V- XXXII V- XXXIII V- XXXIV V- XXXV I-VI IX-XI X-XII X-XIII X-XIV X-XV X-XVI X-XVII X-XVIII X-XIX X-XII X-XIV X-XV X-XVI X-XVII X-XVIII X-XIX X-XII X-XIV X-XV X-XVI X-XVII X-XVIII X-XIX X-XII X-XIV X-XV X-XVI X-XVII X-XVIII X-XIX X-XII X-XIV X-XV X-XVI X-XVII X-XVIII X-XIX X-XII X-XIV X-XV X-XVI X-XVII X-XVIII X-XIX X-XII X-XIV X-XV X-XVI X-XVII X-XVIII X-XIX X-XII X-XIV X-XV X-XVI X-XVII X-XVIII X-XIX X-XII X-XIV X-XV X-XVI X-XVII X-XVIII X-XIX X-XII X-XIV X-XV O-OI O-II O-IIO O-IIIO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIIOO O-IIOO O-IIOO LIST OF ILLUSTRATIONS. xvii
80. Vroom, March 31, 1891 (Domine). PLATE XXVI PAGE 76
86. Vroom, April 5, 1891 (Domine). XXVII PAGE 77
88. Vroom, April 14, 1891 (P. B. Madsenuth). XXXVIII PAGE 78
89. Vroom, April 24, 1891 (P. B. Madsenuth). XXXIX PAGE 79
90. Vroom, April 24, 1891 (P. B. Madsenuth). XXXX PAGE 80
92. Vroom, April 24, 1891 (P. B. Madsenuth). XXXXI PAGE 81
93. Vroom, April 24, 1891 (P. B. Madsenuth). XXXXII PAGE 82
94. Vroom, April 24, 1891 (P. B. Madsenuth). XXXXIII PAGE 83
95. Vroom, April 24, 1891 (P. B. Madsenuth). XXXXIV PAGE 84
96. Vroom, March 31, 1903 (E. A. L. Urbina). XXXXV PAGE 85
97. Vroom, March 31, 1903 (E. A. L. Urbina). XXXXVI PAGE 86
98. Vroom, March 31, 1903 (E. A. L. Urbina). XXXXVII PAGE 87
99. Vroom, March 31, 1903 (E. A. L. Urbina). XXXXVIII PAGE 88
100. Vroom, Nov. 5, 1900 (Antonide). XXXXIX PAGE 89
101. Vroom, Nov. 5, 1900 (Antonide). XXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIXXXXIX
< td style="">XIIII
< td style="">XIII
< td style="">XIV
< td style="">XV
< td style="">XVI
< td style="">XVII
< td style="">XVIII
< td style="">XIX
< td style="">XX
< td style="">XXI
< td style="">XXII
< td style="">XXIII
< td style="">XXIV
< td style="">XXV
XVIII LIST OF ILLUSTRATIONS. | No. | Description | Plate | Page | |-----|-----------------------------------------------------------------------------|-------|------| | 101 | The Solar Corona, July 25, 1923 (Mercury) | XL | 120 | | | The Solar Corona, August 26, 1898 (Sun) | XLII | 121 | | | Aemula, xiviii. | XLII | | | 104 | The Solar Corona, Dec. 22, 1879 (Perry) | XLII | 124 | | | The Solar Corona, 1878 (C. M. Smith) | XLII | 124 | | | The Solar Corona, April 17, 1923 (Smith) | XLII | 124 | | | The Solar Corona, April 7, 1923 (Smith) | XLII | 124 | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII | | | | The Solar Corona, April 7, 1923 (Smith) | XLII  XLIV  XLV  XLVI  XLVIII  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX  XLIX                                                &nb LIST OF ILLUSTRATIONS. xix
182. The Comet of 1600 (iii), July 6 (Caput). PLATE 968
183. The Comet of 1600 (iii), July 6 (Caput). LVI 159
184. The Comet of 1600 (iii), July 6 (Caput). ... 159
185. The Comet of 1600 (iv), May 7 (Planets). LVII 159
186. Halley's Comet, May 19, 1682 (Morsel). LVIII 163
187. Halley's Comet, 1929, on May 3 (Morsel). ... 163
188. Halley's Comet, 1929, on May 23 (Morsel). ... 163
189. Halley's Comet, 1929, on May 23 (Morsel). ... 163
190. Halley's Comet, 1929, on June 3 (Morsel). ... 163
191. Halley's Comet, 1929, on June 3 (Morsel). ... 163
200. The Head and Nucleus of the Great Comet of 1820.
Astronomical Photographs (Photographs) xxii LIST OF ILLUSTRATIONS.
LXII
LXIII
LXIV
LXV
LXVI
LXVII
LXVIII
LXIX
LXX
LXXXI
LXXXII
LXXXIII
LXXXIV
LXXXV
LXXXVI
LXXXVII
LXXXVIII
LXXXIX
XC
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
XCI
LIST OF ILLUSTRATIONS.
xx PLATE PAGES
215. Brook's Comet of 1893 (b). Oct. 21. LXVIII 160
216. Brook's Comet of 1903 (b). Oct. 22. LXXXVII 170
217. Borely's Comet of 1903 (b). [f. r.] - -
218. Giacobini's Comet of 1906 (l) on Dec. 29. LXXIX 180
219. Giacobini's Comet of 1906 (l) on Dec. 29. LXXXI 180
220. Giacobini's Comet of 1906 (l) on Jan. 4. LXXXI 180
221. Giacobini's Comet of 1906 (l) on Aug. 18. LXXXII 180
222. Mellon's Comet of 1908 (l) on Oct. 31. LXXXIII 170
223. Mellon's Comet of 1908 (l) on Oct. 31. LXXXIV 170
224. Mellon's Comet of 1908 (l) on Nov. 4. LXXXV 170
225. Halley's Comet, 1905, on May 25 (Girardet). LXXXVI 170
226. Halley's Comet, 1905, on May 25 (Girardet). LXXXVII 170
227. Halley's Comet, 1905, on May 28 (Girardet). LXXXVIII 170
228. Halley's Comet, 1905, on May 30 (Girardet). LXXXIX 170
The Daylight Comet of 1914 (W. G. Chubb)
LXXXXI170
LXXXXII170
LXXXXIII170
LXXXXIV170
LXXXXV170
LXXXXVI170
LXXXXVII170
LXXXXVIII170
LXXXXIX170
Astrophotographie Comet of 1924 on Sept. 4, [bottom]LXLI170
Astrophotographie Comet of Flight II. E. Barnard]LXLXII170
Fishing for Meteors (Longdonow)LXLXIII170
Meteor Radiant Point in Gemini (Lindley).
Meteor seen on Nov. xii, x688, at New York City.
Meteor seen on Nov. xii, x688, at New York City.
Meteor seen on Nov. xii, x688, at New York City.
Meteor seen on Nov. xii, x688, at New York City.
Meteor seen on Nov. xii, x688, at New York City.
Meteor seen on Nov. xii, x688, at New York City.
Meteor seen on Nov. xii, x688, at New York City.
Meteor seen on Nov. xii, x688, at New York City.
Meteor seen on Nov. xii, x688, at New York City.
Meteor seen on Nov. xii, x688, at New York City.
N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m., N.Y.V., N.y.t. a.m..N.Y.V.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV.NYV,N LIST OF ILLUSTRATIONS. XXI
PLATE PAGE
Metayer seen on Nov. 14, 1865, at Haverhill, Mass. LXXXII - 179
Fireball of Aug. 15, 1830 (first view) 179
Fireball of July 7, 1895 (second view) 179
Fireball of Oct. 18, 1879 (first event) 180
Fireball of Oct. 20, 1879 (second event) 180
Successive Changes in a Fireball (three views) 181
Meteor of Nov. 12, 1863 (plate) 182
Meteor of Aug. 24, 1865 (view of Wight, Feb. 22, 1909) (C. Brodie) 183
The Comet of 1866 (Ll.) 187
Apostle's Changes in Stars rising and setting 187
An Apparent Double Star 193
Diagram for plotting Measurements of a Variable Star 207
Curve of the Variable Star T Cassiopeiae 213
Curve of the Variable Star T Cassiopeiae (second view) 213
The Variable Star A Ursa Minoris 213
Curve of the Variable Star T Ursae Majoris 215
Curve of the Variable Star S Ursae Minoris 215
The Variable Star S Bootis. 215
The Variable Star S Capricorni. 215
The Variable Star S Reticuli. 217
The Variable Star S Cephei. 217
Curve of the Variable Star R Cassiopeiae. 217
The Variable Star R Persei. 230
The Variable Star R Persei (second view). 230
The Pheasants (Tatamis) (F. Roberts). LXXXVIII - 238
Tatamis with two pheasants.
19. The Cluster 2 M Lirae (Sir J. Herschel) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plate number P806
284. The Cluster 3 M Lirae (Sir J. Herschel) ...
285.		 The Cluster 33 and 34 M V Persei
286.		 The Cluster 35 and 36 M V Persei
287. The Great Nebula in Andromeda (Shapley) NCH CXII
288. The Great Nebula in Andromeda (Shapley) XCI CXIII
289. The Spiral Nebula 2 M Cam. Ven. (Sir J. F.) XCI CXIV
290. The Spiral Nebula in Ursa Major (Shapley) XCVI CXXV
291. The Spiral Nebula in Ursa Major (Shapley) XCVI CXXVI
292. The Nebula 81 and 82 M Ursae Majoris XCVII CXXVII
293. Pleasant Nebulae 97 M Ursae Majoris (Earel)
294.Pleasant Nebulae 97 M Ursae Majoris (Earel)
The Great Nebula in Orion (Harvard)
295.The Great Nebula in Orion (Harvard)
296.The Trapezium of Orion (Harvard)
The Trapezium of Orion (Harvard)
297.The Trapezium of Orion (Harvard)
298.The Trapezium of Orion (Harvard)
The Trapezium of Orion (Harvard)
299.The Trapezium of Orion (Harvard)
300.The Trapezium of Orion (Harvard)
The Trapezium of Orion (Harvard)
301.The Trapezium of Orion (Harvard)
302.The Trapezium of Orion (Harvard)
The Trapezium of Orion (Harvard)
303.The Trapezium of Orion (Harvard)
LIST OF ILLUSTRATIONS. XXIII | No. | Name of Object | Plate | Page | |---|---|---|---| | 235 | 30-inch Refractor of the Pulkova Observatory (Ropohl) | CXXVII | 269 | | 236 | 18-inch Refractor of the Radcliffe Observatory, Oxford University | CXXVIII | 270 | | 237 | 18-inch Refractor of the Cambridge University Observatory | -- | 270 | | 238 | 16-inch Refractor of the Lick Observatory (Fawcett & Warren) | CXXXI | 271 | | 239 | 16-inch Refractor of the Lick Observatory (Warren) | -- | 271 | | 240 | 16-inch Refractor of the Lick Observatory (Warren) | CXXXII | 274 | | 241 | 16-inch Refractor of the Lick Observatory (Warren) | -- | 274 | | 242 | Distant View of the Lick Observatory (Warren) | CXXXIII | 275 | | 243 | The Dearborn Observatory, Chicago, Illinois (Hartley) | CXXXIV | 276 | | 244 | The Dearborn Observatory, Chicago, Illinois (Hartley) | -- | 276 | | 245 | The Dubuque Observatory, Dubuque, Iowa (Grubb) | CXXXV | 276 | | 246 | The Dubuque Observatory, Dubuque, Iowa (Grubb) | -- | 276 | | 247 | The Lick Observatory Roof (Warren) | CXXXVI | 277 | | 248 | The Lick Observatory Roof (Warren) | -- | 277 | | 249 | The Lick Observatory Roof (Warren) | CXXXVII | 278 | | 250 | The Lick Observatory Roof (Warren) | -- | 278 | | 251 | The Lick Observatory Roof (Warren) | CXXXVIII | 278 | | 252 | The Lick Observatory Roof (Warren) | -- | 278 | | 253 & 254 & 255 & 256 & 257 & 258 & 259 & 260 & 261 & 262 & 263 & 264 & 265 & 266 & 267 & 268 & 269 & 270 & 271 & 272 & 273 & 274 & 275 & 276 & 277 & 278 & 279 & XXIII - XXXVIII - XXXIX - XL - XLI - XLII - XLIII - XLIV - XLV - XLVI - XLVII - XLVIII - XLIX - LI - LII - LIII - LIV - LV - LVI - LVII - LVIII - LX - LXI - LXII - LXIII - LXIV - LXV - LXVI - LXVII - LXVIII - LXIX - LXX - LXXI - LXXII - LXXIII - LXXIV - LXXV - LXXVI - LXXVII - LXXVIII - LXXIX - CLXIX - CLXI - CLXII - CLXIII - CLXIV - CLXV - CLXVI - CLXVII - CLXVIII - CLXIX - CLXCVI THE GREEK ALPHABET *.* The small letters of this alphabet are so frequently employed in American English that their pronunciation, will be useful to many unacquainted with the Greek language.
a Alpha. r Nu.
β Beta. ξ Xi.
γ Gamma. ο O-micron.
δ Delta. π Pi.
ε Epsilon. ρ Rho.
ζ Zeta. σ Sigma.
η Eta. τ Tau.
θ Theta. υ Vulgaris.
ι Iota. φ Fhi.
κ Kappa. χ Xi.
λ Lambda. ψ Psi.
μ Mu. ω O-mega
xxiv # ASTRONOMY. ## CHAPTER I. ### INTRODUCTION. The scope of the Science of Astronomy.—Its modern development.—The necessity of keeping the treatment of the science within defined limits.—The importance of the study of the heavens to practical Astronomy.—Lord Gregory's book, "Astronomy," without Mathemat- ical knowledge, but with a good deal of common sense.—Practical Astronomy.—Amateurs may disperse with knowl- edge of the stars, but they must have some knowledge of mathematics and optics on part.—The modern application of the spectroscope. The word "astronomy," coming as it does from two Greek words which, in combination, represent the idea of "the Laws of the Heavens," shows that its object is to give an extended scope of the science with which it professes to deal. The fact is that the discoveries of modern times, which supplement the astronomy known to the people who lived a century or two ago, are so numerous and so important that it would be impossible for any one to know all about them. It is not altogether easy always to say where astronomy, pure and simple, ends and something else begins. The chemist, the physicist, the geologist, and others whose speciality is geology, are all concerned, or consider themselves concerned, in the sphere which formerly was limited to pure astronomy, and this includes the planets, the stars, Comets, and Stars, and the phenomena strictly connected with and arising out of the study of these various celestial objects. I 2 # INTRODUCTION. It will be my endeavour in the following pages to keep as closely as I reasonably can to astronomy in its older and more limited sense, because I was to attempt to draw into the atmosphere of this country a subject which, though it may come across the border-line, this book might be open to the objection that it comprised too much of everything and not enough of anything. The Science of Astronomy, taken as a whole, itself embodies several distinct lines of thought and treatment. One of these may be termed Mathematical Astronomy, and perhaps it may be said that this is the most important part of the science assumed by people who have not looked into details to be the cardinal feature of the science, and therefore the one which constitutes its foundation. This is a very true statement of the character of the science. This explains the fact that often when I have recommended the study of astronomy to persons who had never before heard of it, they would say, "I met with remarks couched more or less as follows: "Yes, I dare say it is an interesting subject, but it is too mathematical for me." It is true that mathematics is a necessary part of astronomy, but it is only a necessary part. The other parts are equally necessary. The student who wishes to make progress in astronomy must be prepared to go through all the highest mathematics, it is a mistake to suppose that unless this is done it is no good taking up the subject at all. The view which I am now presenting is not new. It was first brought forward by Mr. Beckett-Jenson, Q.C., who published a very useful little book with the pointed title of "Astronomy for Beginners," in which he says: "If you wish to understand the reader will find that I have trodden in the footsteps of my departed friend, but nobody could possibly assimilate Lockhart's work without having first read what was completely sub genere in every sense of those useful words." Mathematical Astronomy may otherwise be spoken of as DIFFERENT BRANCHES OF ASTRONOMY. 3 Theoretical Astronomy, because it covers the theories of the movements of such of the heavenly bodies as move, and the laws which govern their movements, and so enables the advanced student to understand how the planets move, and to detail the motions of the planets and other moving bodies whose orbits are known, in the sky from day to day and month to month and year to year are set out in our almanacs. In addition to this, one branch of this, we have what may be called Descriptive, or Visual Astronomy. This represents, with respect to the heavens, the work done by the newspaper re- porters who describe the progress of the sun across the mundane. In other words, the student of astronomy who concentrates his attention on the descriptive side spends his time looking at the stars through a telescope or with a slide, with his pencil or record with his camera what he has seen, and perhaps to commit to writing his observations for the use either of himself or others. This is not only a very useful thing, but is the popular, everyday side of the subject, and that people with fairly good eyes and a certain amount of common sense and a little knowledge of mathematics can do much good and profit, even although they know little or nothing of mathe- matical astronomy, and have no great acquaintance with the third or last subdivision of the science which is called Practical Astronomy. Practical Astronomy deals with instruments, processes, and methods—with the principles, the construction, and the use of them—of all those things which enable us to make instrumental measurement of angles and distances, and the tabulation of observations and the drawing of conclusions from these. As in the former case a student may do a good deal of useful work with his eyes without troubling himself much or at all with any mathematical calculations. He may derive much de- light from it, in connection with descriptive astronomy, using th telescope to help him. And this, though he knows INTRODUCTION. Little or nothing about the theory and construction of telescopes, or how they are put together, or the names of the different sorts of lenses which he uses each time that he handles his telescope. In mentioning the range of astronomy it is necessary to mention also the various branches or subdivisions of the subject which goes by the name of Nautical Astronomy—the application of the science to the determination of longitude. But that, of course, is entirely beyond the scope of this work. I hope that the foregoing ideas will be realised by those persons who have read this book, and that they may also realise the fact that they can obtain a great deal of pleasure and profit from a study of such departments of astronomy as may be readily reached without great exertions of the mind, and without any special apparatus other than a good telescope. There is another more subject which must in brief form find place in this volume—and that is Spectroscopy. It is only within 50 years or so that the spectroscope has been brought into general use as an accessory to the study of astronomy; and it is only within a few years that its importance has come to be recognised in the minds and work of those who, going beyond the modest aims of this volume, desire to dive into hidden things which lie at the very heart of the most subtle eyes of the casual student of nature who takes up astronomy. In order not to burden the pages of the book with uninviting masses of figures, statistics, and other material which might be considered as being out of place, I have decided to exclude them altogether, and to confine myself to a certain number of points which I consider are essential to an understanding of the subject. These points are dealt with in an Appendix, where they will be more accessible for consulta- tion and comparison. A page from a book titled "Introduction" discussing astronomy and telescopes. CHAPTER II. THE SUN. Important position occupied by the Sun.—Its general appearance.—Its metallic surface. —Gravitation! probably the best word to describe the Sun's motion. —The Sun's spots. —Their peculiarities of spots. —Periods of the Sun's rotation. —The influence of the Sun on terrestrial phenomena. —The periodicity of the spots—Aurora.—Terrestrial Magnetism.—Sunspots and magnetism. —The Sun's magnetic poles. —The Planets on Sun-spots.—Wilson's theory respecting them.—Vortices in the Sun's atmosphere. —Sun-spots at different seasons of the year.—Noable large spots. —Light- and heat-giving effects of the Sun. We are so accustomed to see the Sun and feel its heat-giving effects that we are apt to lose sight of the important position which it occupies in the Universe—or perhaps I ought rather to say, in our Solar System—and this is one reason why the sense of the term, extends far beyond our Solar System, which is probably only one of many systems, and perhaps even not the most important system in the Universe. In his "Book" on his many books, "The Sun: Ruler, Fire, Light, and Life of the Planetary System." The phrase was a comprehensive one, but did not include all that is implied by it. Everybody, I suppose, knows—at any rate, in a general way—that the Sun is the centre of our Solar System, not only in respect to its own motions, but also in respect to those of other bodies in it, but as the immediate and prior source (humanly speaking) of all light and life on the Earth; moreover, it is also the central force which keeps everything going. To pursue this 6 THE SUN. thought further would lead me into a disquisition on the Law of Gravitation and the laws generally of Celestial Motions, which it will be understood from the previous chapter, would be of little use to the reader. If we look at the Sun soon after sunrise or towards sunset, or through a fog, or through a smoked or dark-coloured glass, what do we see? Apparently a bright disc with a circular outline. But this is only a true circle, though, when it is viewed near sunrise or sunset, the circular outline is slightly distorted. To the naked eye this disc appears as a flat surface, but owing to its great luminosity it has the most powerful and useful heat-distributing properties. But this is very poor description of what the Sun really is. The Sun is a star, and by means of some simple calculations, determines it to be very large and not flat, but globular—spherical—a ball, in fact. To the naked eye the Sun seems to have no outline whatever. With a telescope, however, matters are far otherwise. The surface appears speckled or stippled, and near the limbs or edge of the circle there are often seen black spots. These black spots are sometimes visible, the centre of the Sun being always brighter than the edges. This latter fact is a very important one, as it shows that there is no heating and streaks and spots depend on certain physical causes, which are not in every respect capable of full explanation. A great many words and phrases have been brought into use in describing the Sun, and I think it advisable to give an idea of the appearance of the surface of the Sun. "Willow-leaves," "rice-grains," "shingle beach," "mothing," "stipping," "granulations," "spots," etc., are all terms which have been employed, first by one and then by another observer. The last-named term is decidedly objectionable, because it suggests that there are granules on the surface of the Sun. On the whole, because of its vagueness, I am inclined to prefer the word "granulations" as being most expressive of the THE SUN'S SURFACE. 7 ordinary appearance of the Sun in telescopes of sufficient size to show anything. A great controversy raged over several of these phrases half a century ago. The term "willow-leaf" was put for- ward by Mr James Nasmyth, the inventor of the steam-hammer, who in his later years became a great observer, being also very skilled in the art of painting. In 1850, when the surface of the Sun exhibited the appearance which would be presented by a large mass of leafy-leaves if flattened out and lying pro- minently on the ground, he called it "willow-leaf". Though the term "willow-leaf" did not meet with general acceptance, it set astronomers thinking how they could best describe what appeared to them. It was found that all agreement was not smooth and uniform, as a plane slab of oil appears smooth and uniform. Langley's well-known picture of what he called a "Typical Sun-spots" is a good example of this idea, though I do not think he used the words. [Plate II] Sir W. Huggins, one of our greatest and most experienced experimenters, made many observations at first hand at the time, and summarised his conclusions by giving the preference to the word "granule", because no positive form is implied by its use. He thought that it represented something which could not represent what was seen in small telescopes, but that there was thereby implied a definiteness of shape which to some extent diminished the value of the word "granule". This view was resorted to. He thought, however, that it might safely be said that these objects, whatever their nature, did affect an elongated, oval, or lenticular form. The theory has not been seriously disturbed by later discoveries, and on the whole, it may be said that the general surface of the Sun presents a granulated appearance to which nothing better can be substituted. But I believe that I think the word is too precise. Another word in use is "pore"; and this has something to recommend it, because when the 8 THE SUN. spots (presently to be described) break out, they often start from a pore as a place of origin. Other similes have been suggested for the granulations on the surface of the Sun. An American astronomer has likened them to the snow-white ends of coral. He says that the picture Fig. 2.—Madrepora Specifera. An East Indian Variety of Coral. here given (Fig. 2) of a specimen of East Indian coral in the Natural History Museum at Williams College, Massachusetts, "held at arm's length, and viewed with eyes partially closed, gives a tolerable idea, though on an enlarged scale, of the appearance of the solar meeting as seen in the largest telescopes." GROWTH OF SUN-SPOTS. 9 The spots on the Sun are a very notable feature, and now and again become a very striking feature visually, and the whole history of their observation is one of intense interest. Before the invention of the telescope, we knew nothing of them or thought of them known, because it was only at long intervals that a spot sufficiently large to be seen with the naked eye became visible. And even when telescopes did come into use, they were not used systematically enough to give any long time—more than two hundred years—before observation of them came to be made systematically, and some 250 years before it was possible to say that they had been observed at regular intervals upon a recognisable law of periodicity. Before dealing with this law we will consider what is meant by "some day" in connection with the Sun's spots. We will suppose that on a certain day an observer turns his telescope, armed with a suitable dark glass, on to the Sun, and that he notices nothing but a small black spot. He will then turn his telescope away, and speak of this spot as having been observed. The next day he speaks of another spot, and so on until he has observed several spots. On the following day he detects a little blackish point. If he watches this point during several days it may grow larger and more irregular in shape, and eventually develop into two blackish points. In such case the two will separate from one another more and more, become larger in size and probably more irregular in shape, whilst, when they have grown to a certain size, they will begin to move apart from each other. This process will continue until the two original spots, so that a very broken but somewhat regular irregular group or chain of spots will have grown up. Now if we take any one of these spots and follow its course as it were the leader of the group, the word "forward" being used to indicate the spot which is at the end of the group seeking to reach the Sun's centre, we shall find that after a while it will be found that the group is moving over the Sun's disc, which will be from E. to W. It is unnecessary to give an explanation here. Whether a spot is endowed with an absolute motion of its own is an inde- pendent question which may, or perhaps may not, have to be I0 THE SUN. answered in the affirmative in any given case; but, inasmuch as the Sun is ended with a motion of rotation on its axis, every spot, whatever its inherent permanency may be, will be very soon noticed to be constantly in motion across the Sun's disc. The Sun rotates on its axis from E. to W., in about 25½ days, and thus presents a new view for more than about half of this period--actually about 13 days--for a reason to be presently given. If a spot on the Sun's disc has a lifetime of several weeks, it will, after disappearing on one edge of the Sun, reappear a fortnight later on the other edge, and so on and so on, it may be supposed that it would never disappear at all. Let us now go back to the chain or group of spots with the consideration of which we started. This will be seen to undergo increasing changes--the constituent spots increasing in number, and some of them becoming smaller by losing their light; or they will all disappear, being smothered or blotted out by the onward rush of the waves of luminous matter which continue to issue from the Sun's surface. The name of "photosphere" (or shell of light) has been given to the part of the Sun's disc on which we see the Sun's light. The spots on the Sun do not always appear in groups or with a gregarious tendency, for sometimes we may see a single spot which apparently has no neighbours or belongingers. Near such spots we may find others, but these are not necessarily connected with each other; on the other hand, it may retain its individuality for some time, increasing in size or diminishing, but retaining during its whole existence a certain position relative to the Sun's disc. It is more or less approximates to a circle, like a hole bored in a piece of wood by a gimlet, which, when removed, shows the edge of the wood. So much for the personal appearance of an average Sun-spot, but a good deal remains to be said on the subject. When a spot is beginning to disappear it does not always do so by CHANGES IN SUN-SPOTS. 11 a uniform contraction all round its circumference. Not unfrequently the final closing up will be preceded by a bridge of luminous matter darting over the dark area, and forming for a moment a kind of a bridge over the dark area, making indeed the whole appearance to be that of two small spots side by side instead of one large spot. The mass of material which is available for an account of A diagram showing a circular object with a central dark area and surrounding lighter areas. The text "Fig. 3. - Spot on the Sun, Aug. 14, 1868." is below the diagram. the Sun, even if only limited to the standpoint of visual observation, is so great that it is very difficult to know how much to attribute to each individual spot and how much to the Sun. Something more, however, needs to be said as to the physical appearance of the Sun's surface and of individual spots. All spots are surrounded by a bright ring, which we call the dark spots; but that adjective is really only a relative term, and must not be pushed too far. The ordinary dark central THE SUN. part of a spot is commonly called the Umbra (Lat. "shadow"). This is surrounded usually by a fringe of a lighter shade to which the name of Penumbra is applied (Lat. *peno*, almost; see p. 30). These two portions of an ordinary spot are generally very distinctly defined, and the umbra does not usually pass into the penumbra, but remains distinct. But occasionally it happens that, within the limits of the Umbra, there may be noticed a small patch of deeper blackness to which Dawes applies the name of "intensum" (Lat. "intense"), and which is an example of ordinary nucleus as "intensely black" is again a misnomer, for it is only relatively dark, showing in reality, according to Langley, a violet purple hue. The nucleus itself has its own colour, and several spots may be included in one penumbra. Moreover, the outer edges of a penumbra will usually appear darker than the interior portions. This, no doubt, is due to the fact that the outer edge of a penumbra is generally of a very irregular outline, but not always so, for sometimes the outline bears a certain resemblance to that of a circle. In some cases also the spots themselves are often very irregular in shape, yet, on the other hand, they are sometimes very compact and symmetrical. A remark still more true of nuclei where a nucleus exists. The duration of the existence of a spot is a matter of great interest. It may appear and disappear in the course of a few hours ; or it may remain visible, disappearing and reappearing several times by virtue of the solar axial rotation, as already pointed out. Sometimes it appears that the spot is absolutely fixed in its position during the period of its visibility. Some spots certainly have a motion of translation of their own which makes them appear to rely upon their disappearance and reappearance as a means of deducing the exact period of the Sun's rotation. FIG. 4 PLATE II. A Typical Sarsaparil (S. P. Longstaff) Figs. 5-8 PLATE III. Oct. 22, 1903. July 31, 1906. Feb. 7, 1907. May 6, 1907. Disc of the Sun, showing Spots (E. W. Harlow). Figs. 9-12 PLATE IV. July 15, 1907. May 4, 1908. Aug. 3, 1908. Sept. 7, 1908. Disc of the Sun, showing Spots (E. W. Barlow). Figs. 13-15 PLATE V. A series of three images showing sunspots on solar charts. Oct. 14th 9:07 A.M. Oct. 18th 9:07 A.M. A graph showing the decrease in solar activity over time. Nov. 3rd 9:25 A.M. The Great Sun-spot of 1865 (Howlett). 33 APPARENT MOVEMENTS OF SUN-SPOTS. 13 However, as the result of multitudes of observations by various observers, we shall probably be not far wrong in putting this 25 to 30 years ago. It is only natural to observe that these figures are not a measure of the time which a spot takes to disappear and reappear and disappear again. This is because the Sun itself is a moving body, with its rotation, on its axis, of the Sun itself, because between the com- mencement of a spot at the eastern limb and its arrival at the same point on the Earth has passed more than one revolution of the Sun. So, as we speak, to turn a little farther than one revolution in order to be again abreast of the Earth. The following are some special features of the Solar Orb as made manifest even to the casual observer. In the first place, the intensity of the solar light is greater in the middle than at the edges. This is a consequence of the obvious fact that, in looking at the edges, we are looking through a thicker layer of the outer coating of the Sun than when we look straight at it in the middle. The second question is: "What is the Sun?" and "How is it put together?" These questions are difficult, and are very To say that the Sun is not a solid body as the Earth is, and with a luminous atmosphere surrounding it, is a statement altogether inadequate, and beside the mark. The general opinion is that there is nothing solid in the Sun, but that it is an enormous mass of gaseous matter of various kinds, surrounding which are two or more shells or layers. The outermost layer consists of a mixture of hydrogen gas, and divers metallic vapours. To the innermost of these layers the name of Photosphere has been given, and this is the visible source of the ordinary solar light which reaches us. Next outwards comes the Chromo- sphere, a thin casing of luminous matter, chiefly hydrogen 14 THE SUN. gas, and the seat of the Red Flames seen in total eclipses of the Sun : whilst, still reckoning outwards, there is a third shell of spots, which have been given by some, but shall have to consider further some of these spots, and the character of the changes which traces of eclipses of the Sun. The spots do not appear precipitously all over the Sun. They are found at either of the poles or anywhere near them. They seldom reach a greater latitude, N. or S., of the Solar Equator than about 30° to 37°; but, even within these limits, they are very rare. The spots are generally dis- buted—that is to say, they are rare at or near the Solar Equator, and perhaps may be said to be most usually seen in latitudes between 30° and 50°. This is owing to a rule more numerous and of greater generality in this part of the solar sphere, especially between the latitudes of 12° to 15°. I shall return to recur to this question of the distribution of the spots in latitude after having considered their nature. This is a very interesting and important detail. For more than two hundred years after the invention of the telescope and of spectacles, when many new spectacles, they were regarded as hagard manifestations of some sort of outbursts on the Sun's surface, the causes of which were quite unknown, and least of all were imagined to be subject to any law. In 1825 a German amateur named Schwabe, who lived at Dessau, commenced a systematic observation of the Sun during his leisure hours. He was able to see it for an average, about 300 days in every year, and he carried on such observations for about 30 years, when he reached a point where he could no longer continue them. He began by suspecting that, if he observed the Sun through a sufficiently long number of years, he would find that the spots were subject to a law or laws of some sort. Twelve years enabled him to satisfy himself that there was a periodicity about them; he then spent another 6 years in trying to Figs. 16-18 PLATE VI. A starry sky with several bright spots. I A cluster of bright spots, some connected by faint lines. 2 A large, dark spot surrounded by a few smaller spots. P A large, dark spot with a bright center. R Sub-spots. (1) Oct. 30, 1905. (2) Nov. 15, 1905, showing granulations and faculae (Barlow). (3) June 22, 1889 (Mrk.). 14 Figs. 19-26 PLATE VII. Aurelia Sept. 18 Oct. 3 Sept. 29 Oct. 5 Sept. 13 Sept. 14 Sun-spots in 1882 at Various Dates (Cortic). PERIODICITY OF SUN-SPOTS. 15 impress astronomers with the truth of his opinion, and in the course of another period of 12 years or more he was able to convince mankind that the periodicity of the Sun-spots was absolutely assured; and, to cut a long and very interesting story short, it will suffice for me now to say that, as the sunspots have been observed since 1610, they have occurred slightly over 11 years. Or, to put it in another way, 1911 having been a year of practically no spots at all, 1921 has been a year of practically no spots at all, and so on until about 1916, when they will be very abundant, reaching their period of maximum; they will then diminish until 1920 or 1923, when very few, and during many months none at all, will be visible. This question of periodicity and its amount of 11' years is now established to a dead certainty. It must be stated, however, that this period does not occur exactly every 11 years but between two maxima, but that 64 years lapse between a maximum and the next minimum, leaving 48 years as the interval between successive maxima. The exactness of these figures is not precise figures for the intervals are not, however, quite assured. We are not yet able to put a very explicit interpretation upon this 11-year period, though there are some incidental indications which suggest that it may be due to some cause takable. These include the diurnal variation of the magnetic needle and manifestations of the Aurora Borealis. It is beyond doubt that the auroral phenomena are connected with magnetism and the Aurora. It must suffice, therefore, for me to state that the magnetic needle is subject to a minute change of an oscillatory character in the nature of an effort on the part of the earth's magnetic field to restore itself. These minute vibrations are not uniform, but vary in extent during a period of years now recognised as being about 11 years. Manifestations of the Aurora also vary from month to year during 48 years. And now comes the peculiar conclusion that this mode of terrestrial magnetic displays and of auroral 16 THE SUN. manifestations are synchronous with maxima of Sun-spots, and minima with minima. The phenomena which have just been pointed out will be far more easily realised by an inspection of the annexed diagram than by the fullest verbal description. The rise and fall of the sun-spots are represented by the two curves, each showing both the extent of the changes during the dates thereof; and a cursory inspection of the three divisions of the diagram will show at once the coincidences of maxima and of minima and of dates. With these facts before us it is not permissible to doubt that there is some intimate connection between certain events which occur on the surface of the Sun and those which take place on the Earth. What the nature of this connection may be cannot quite definitely be stated, but that electricity is concerned in the matter in some way or other seems perfectly certain. This fact has been clearly established by several observers, as will be stated. For instance, on September 1, 1859, two English observers in different places were examining a fine group of Sun-spots when they observed a bright flash of light, followed by a bright light burst front in front of both spots. They were at first thought to be due to a fracture in the screen attached to the object-glass of the telescope; but such was not the case. The particles were seen to move across the field of view for a short time itself. They remained visible for about five minutes, during which time they moved a short distance. A remarkable fact was also added. Simultaneously there happened a great disturbance of the magnetic instru- ments at the Kew Observatory, followed 16 hours afterwards by a violent magnetic storm, during which the telegraphs were interrupted. Aurora borealis was observed over several places, stand alone for, on several more recent occasions large Sun-spots and marked disturbance of instruments recording terrestrial magnetism have been noticed as contemporaneous events. Probably the truth is enshrined in the following A diagram showing three divisions of a graph depicting sunspot activity. SUN-SPOTS AND WEATHER ON THE EARTH 17 words of Mr. H. C. Lewis, an assistant at the Greenwich Observatory: "The theory is not improbable that Sun-spots are the result of some physical or magnetic storms, and that Auroras are the result of a disturbed electrical condition of the Earth caused by induction from the Sun." The common cause for auroras is "the solar wind," says Prof. A. E. Maunder has summed up the situation, as regards the question of solar magnetism, thus: "It is evident that, besides sending to us light and heat, the Sun sends us some kind of influence which comes only from certain portions of its surface. We find that there is a definite spot on the Sun's disc, and another spot on a definite portion of the Sun's disc." The question is often mooted as to whether any connection can be traced between the prevalence or absence of spots and the occurrence of thunderstorms. This question is open to this is exceedingly contradictory, and great names are to be found ranged on both sides of the controversy, and it is really impossible to present any trustworthy definite conclusions. The explanation given by Prof. A. E. Maunder is indepen- dendent standpoints, namely, terrestrial temperatures as dis- tinguished from terrestrial rainfall. Perhaps it is in respect of temperatures that the evidence is most conclusive. Thus the English physicist, Sir W. Thomson, for instance, Wolf, a well-known Swiss observer, considered that he had found decisive evidence "that years rich in solar spots are in general drier and more fruitful than years poor in solar spots." On the other hand, Sir W. Gautier, discussing 62 sets of observations, extending over 11 years and taken at various places in Europe and America, arrived at exactly the opposite conclusion. Profes- sor C. P. Smyth considered that a great wave of heat passes over the 2
18 THE SUN.
Earth every 11 years and a fraction, and nearly coincident with the beginning of the increase of each Sun-spot cycle. A German observer, Steen, collecting materials obtained during 30 years ending with 1903, considered that there was evidence that the maxima and minima of thunderstorms occur at about the period when Sun-spots are at their maxima and minima respectively.
Perhaps it may be added with safety, though I shrink from dogmatizing on the matter, that the year's high temperature is connected with the beginning of the Sun-spot cycle, which was put forth by J. Stone about 1876, as the result of 30 years' observations at the Cape, and by Abbe as the result of 50 years' observations at Paris. This would explain a confirmation in the long prevalence of intense heat in July which is a year of unusual deficiency in Sun-spots. The question has been seriously mooted as to whether spots on the Sun indicate a solar cycle than the 11 year cycle, and whether planetary influences come into the question.
It seems that an affirmative answer must be given on both these points. The number of sun-spots varies greatly from year to year, indicated by spots, has two further periods of 554 years and 166 years respectively; the former period being made up of 5 normal cycles and a period of 13 normal cycles. This is a number which needs and deserves further investigation.
The following table of dates of recent Sun-spot maxima and minima will be useful for reference:—
1800– Minima.
1806– 1807–
1820– 1829–
1840– 1850–
1849– 1901–9
1906– 1911
PLATE VIII.
Figs. 27-30 Jan. 31 Feb. 1 Jan. 3 Feb. 7 Jan. 5 Feb. 10 Jan. 13 Feb. 13 Jan. 28
COMPAREATIVE
Size of the Earth
The Great Sun-spot of February 1905. A series of images showing sunspots and a comparison with the size of the Earth. Figs. 31-35 PLATI IX. Changes in Spots as they approach the Sun's Limb. (LE. W. Barlow.) 1906, (1) May 23; (2) May 24; (3) May 25; (4) May 26; (5) May 28. WHAT ARE THE SPOTS. As regards planetary influences, there is a considerable amount of testimony to show that the prevalence of Sun-spots depends on several causes, one of which is the motion of the Moon with respect to the Sun. Wolf thought he found traces of an influence exerted by Venus in the course of its annual revolu- tions, but this view has been abandoned. The influence of Mercury and Jupiter might also be brought in as exercising some effect. The influence of Venus, assuming it to be real, implies that the planet causes spots to break out in longitudes of the Sun when it is at aphelion. This is a very plausible supposition, since spots have been started by Venus, its maximum development does not take place till, by the Sun's rotation on its axis, the place of greatest activity is reached. In spite of the distinguished names which are attached to some of these surmises as regards planetary influences, I do not feel inclined to rely very much upon them. In the case of the shadow theory, the mistakes being made in their interpretation, owing to the general complexity of the whole subject and the difficulty of proving connections of cause and effect. A great deal has been done during recent years to the Sun by late years by astronomers generally throughout the world, with the especial object of determining, if possible, what are the causes of spots. But though many physical circum- stances which may be supposed to govern them. Much pro- gress has been made, but, nevertheless, more information than we at present possess is needed. The oldest and most trustworthy data are those given by Sir William Herschel, a certain Professor Wilson, of Glasgow, as modified by Sir W. Herschel. This assumed that the Sun is surrounded by two layers, one luminous and one non-luminous like the skin of an onion, the outer one being luminous (hence termed the Photo- sphere, as already mentioned) and the inner one non-luminous, and that the spots are rents or apertures in these two skins through which we see revealed the solid body of the Sun itself. Bearin' mind that it is now the received opinion that the 20 THE SUN. Sun is not a solid body, it must, nevertheless, be confessed that the Wilson theory has something very attractive about it, in view of what we have seen with regard to the appearance of spots with telescopes. Suppose we find a spot somewhat symmetrical in shape, and in the middle of the Sun's disc, and watch its gradual change of place towards the edge by reasons of diffusion, and suppose that this spot is a sun-spot, which of course undergoes foreshortening, in accordance with the natural law of foreshortening when a globe is turning on its axis. We shall then see a spot which appears to be at one point, at which the spot is approaching; so much so that the penumbra on that side will have ceased to be visible whilst a certain amount of umbraity exactly opposite still remains in view. A person looking at such a spot would say "I cannot hardly fail to be impressed with the feeling that his eye is resting on a cavity with sunken walls, so to speak, all round it, not necessarily perpendicular, but rather in the form of a funnel." This theory of the nature of a Sun-spot finds confirmation in the fact that now and again a large spot, when it is passing out of our sight, leaves behind it a faint trace which generally appears as a notch in the outline of the disc--a fact which distinctly favours the idea that the spots are depressions, and not projections. The spots are usually situated somewhat above the general surface of the Sun. Spots as notches have not infrequently been recorded by observers; a notable case occurs in a photograph taken at Dehuran-Din, in India, in 1884. The photograph was taken by Mr. H. H. Fowler (who put forth work in America by Professor Hale (a highly skilled observer) that he had detected signs of Vortices, or cyclonic action of a magnetic nature), who was visiting India during summer. Professor Hale has investigated the subject. I am not at all sure that this idea ought to be considered "new," because I have in my possession a drawing by Howlett dated May 17th, 1865, which is actually labelled what it shows, "Interesting Vortices Group." FACULÉ. 21 a very exhaustive fashion, and his conclusions have met with much acceptance, but it is only fair to add that signs of cyclical errors in the observations, and of the great irregularities to take up sometimes a spiral form, were obtained and noted many years before Hale went to work by observers as early as Huggins and Secchi in the sixties and seventies of the last century. The stars are so numerous, and their light so delicate and intricate one, requiring skilled observers and large special instruments, and therefore is a subject subject to much error. Before passing away from the Sun from a sight-seeing standpoint, I must not omit a few words about solar faculae. These are spots which appear to be located in the equatorial regions of the Sun, and they either move with it, or often running somewhat in a N. and S. direction, are generally of no particular form, though perhaps a policeman's trouser leg would be a good figure to represent them in their shape. Without exactly pretending to say what they are in constitution, it seems at least certain that they are elevations or ridges on the surface of the Sun, and that they are masses of luminous matter floating in or on the Photosphere. It would seem that they have some sort of association with spots, in so far that they are often to be found just outside the penumbra of a spot, or even within it, but this is not always true where a spot has actually disappeared. [Fig. 36-37, Plate XI.] The fact that the position of the Earth with reference to the Sun changes its inclination during the year, owing to the Sun's axis is inclined to the plane of the Ecliptic, has this result, namely, that a spot on the Sun, if attentively followed during the course of a year will be seen to move from east to west; it is found to pursue a path which differs with the season of the year. In June and December a spot will seem to follow a straight path diagonally upwards in the former case, and diagonally downwards in the latter case; whilst in March Late July, a trekch. 22 THE SUN. and September the apparent path will be curved—with the convexity in the former case towards the North Pole and with the convexity in the latter case towards the South Pole. Astronomical writers of popular books generally try to excite their readers by giving a wonderful array of figures supposed to prove that the Sun is much larger than it really is, but I am not convinced of the usefulness of such statistics, and I shall give but a very few. It may be taken for granted that no Sun-spots are visible at the naked eye unless they have a diameter of 30000 miles, and that no Sun-spots of greater size than this are on record. For instance, on March 15, 1858, a spot was visible having an angular breadth of 3°, or about 60000 miles. This chapter may be brought to a close with a few statistics. The distance of the Sun from the Earth, or, to put it more conveniently, the Earth's orbit, is taken as average 93,000,000 miles, which varies slightly in the course of January and July, when, owing to the ellipticity of the Earth's orbit the Earth is nearest the Sun and farthest from the Sun. In England (in the Northern Hemisphere) people in the Southern Hemisphere generally experience colder weather in January than we do in July, though we are nearer the Sun in January than they are in July. This fact is easily explained. The explanation is exceedingly simple. The meridian altitude of the Sun in January is low, and its rays reach us through a certain thickness of atmosphere, and much of the heat is absorbed by it. In July the altitude of the Sun is very considerably higher, and its rays descend upon England and the Northern Hemisphere more nearly perpendicular to our surface. Hence they pass through a thinner depth of atmosphere to absorb them. The diameter of the Sun is about 32° of arc (say just over 7°), and about 800,000 miles. The Sun's mass, or attractive power, is 335,000 times that of the Earth, and about 750 times that of all the A diagram showing the relative sizes and distances of celestial bodies. Figs. 36-37 PLATE X. June 5th, 1881. Nov. 28, 1884. Faculae on the Sun (Cortie). FIG. 38 PLATE XI. The Red Skaters in 1855. [3] HEAT-GIVING POWER OF THE SUN. 23 planets put together. The density of the Sun is about 13 times that of water. These figures are an indication of the comparative lightness of the Sun as a matter of weight. Many experiments have been made to arrive at an idea of the heat-giving and of the lighting power of the Sun. The conclusions as to the heat-giving power, are not very definite, but weighty. For instance, it has been stated that our annual share of the heat would melt a layer of ice all over the Earth 100 feet thick. It has also been stated that the heat from a freezing-point to boiling-point; whilst the direct light of the Sun has been supposed to be equal to that of 5500 wax candles of one foot diameter at a distance of one foot from the observer. Such figures as these are not likely to be true. "The Sun is Wonderland." Thus attempts have been made to calculate and state by figures the heat-giving power of the Sun, it must be obvious that all such calculations can only be, if not quite imaginary, yet very wild and indeterminate. It is, however, worth while to note that in all these cases we are dealing with Sun-rays being what they are. For instance, in constructing the Breakwater at Plymouth, the men working in diving-bells at a distance of 30 ft. below the surface had their clothes burnt by the rays from the Sun's disc, which was then at top of the bell to let in the light. Some years ago the bedroom curtains in the house of a friend were set on fire by a ray from the Sun; and I once read in a book of military history relating to Sir R. Abercrombie's expedition to Egypt in 1801 that when he was in camp near Alexandria, a tent which had been fitted up so that every day at 12 noon the gun was fired by the sun igniting a charge of powder by means of a burning-glass (i.e. a double-cone lens), which focused the Sun's rays on the touch-latch, and so ignited some powder. It would not be possible, nor indeed desirable, in my limited 24 THE SUN. space to describe in any detail the various pictures of Sun-spots given in this chapter, but the one dated August 11, 1881, will readily show the reason why the appearance of the Sun's surface is so unlike that of the Moon's. The wave-like structure of the penumbra will be readily realised, whilst on the southern side of the vast depression (for the penumbra is a depression thousands of miles deep) there will be seen a series of small spots, which appear to be flowing up to and over the edge of the centre. The picture also shows a long straggling line and small spots, which, though they have been described as already been mentioned, is often a feature of a prolonged and extended group of spots. It may help to convey an idea of the magnitude of these spots by comparing their outer diameter with that of the Sun under consideration sufficiently spacious for the Earth to be dropped into it without touching the penumbra on either side. The following table gives at various dates as observed at the Stonyhurst College Observatory, and have been kindly placed at my disposal for reproduction in this collection. A spot is said to be active when its diameter April 1882 show the daily changes in a spot in the course of a week or less. The spot dated Nov. 17, 1882, was accompanied by a great magnetic storm and a magnificent display of aurorae. The spot dated June 30, 1883, Oct. 5 and Sept. 13 and Sept. 15, 1883, are examples of spots with double penumbra. Fig. 37, dated June 28, 1884, gives the whole of a spot with a large central depression and remarkable manifestation of faculae. The picture dated Nov. 28, 1884, shows a very fine group of faculae on the E. limb of the Sun. The following plate [VII] dated February 1905 gives the life-history of what became a great spot from its development from a few small spots. Fig. 38 is a representation, taken from a photograph, of the red sunspots ("Red Light") which created so much sensation in the autumn and winter of 1883, and which were regarded as KRAKATOA SUN EFFECTS. one of the most remarkable solar-terrestrial effects of modern times. The strange feature of the Red Light was the peculiar halo which it caused around the Sun by day, and its long duration after sunset. At that time, and during the early evening, the sun was seen to rise or set in a deep rose, and it seemed to far up towards the zenith with a bright spot at its highest point. There was also a bright spot and coloured arch in the E., opposite the point of sunset, as if due to a reflection of the sun's rays on the water. This was succeeded by a rapid arch succeeding arch with changing colours as the sun sank lower and lower. It will be remembered that the phenomenon was observed on 26th August, 1883, when a cloud of dust from an active volcano on the island of Krakatoa, near Java and it was supposed that the dust was belched forth in such enormous quantities that it was carried round and round the World by the Earth's axial rotation. CHAPTER III. THE MOON. Next after the Sun in popular interest—Moon seen visible after being hidden by the Sun—Appearance of the Moon—General physical aspects—Its mountains—The walled plains—The rills —Morphology of the Moon—Rocks on the Moon—Rocks on Earth —Resemblance between lunar and terrestrial volcanoes.—Names applied to the various parts of the Moon—General appearance of the Moon—General appearance of a crater—Changes in their appear- ance with time—The craters of the Moon—Their origin—Very com- plex.—The Librations.—The Harvest Moon.—The Hunter's Moon.—The Moon's influence on human beings.—The influ- ence of the Moon on clouds.—Influence of Moonlight on human beings, a fallacy.—Some statistics. NEXT after the Sun the Moon ranks as the celestial object best known to the intelligent man of the Earth though he may not, under ordinary circumstances, see it every day. This is owing to the fact that, during the third quarter of the Moon's monthly circuit of the heavens, it only shines when most of us are awake. It is therefore visible at night, either very early, or late or very late, in order to see it. Indeed, except for a certain number of hours, usually considered for good cycling purposes, when the Sun is out of sight but the Moon is visible, weather permitting, throughout the whole of its monthly journey round the Earth as projected on the sky. The phases of the Moon—that is to say, the ever-changing outline of its illuminated portion—are so well known that it A stylized drawing of a crescent moon. Fig. 39 PLATE XII.
Class Name Number Area Alt. Alt. Alt. Alt.
MOUNTAIN RANGES MOUNTAIN RANGES 21 CASCADES P CASCADES P CASCADES
QUADRANT QUADRANT 27 CASCADES P CASCADES P CASCADES
QUADRANT QUADRANT 28 CASCADES P CASCADES P CASCADES
QUADRANT QUADRANT 29 CASCADES P CASCADES P CASCADES
MOUNTAIN RANGES MOUNTAIN RANGES 30 CASCADES P CASCADES P CASCADES
MOUNTAIN RANGES MOUNTAIN RANGES 31 CASCADES P CASCADES P
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A B C D E F G H I J K L M N O P Q R S T U V W X 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Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А В С Д Е Ф Г И Й К Л М Н О П Р С Т У В Х Я З А в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а в с д е ф г и ю к л м н о п р с т у в х я з а v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a v s d e f g i y k l m n o p r s t u v h y z a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_y_z_a_v_s_d_e_f_g_i_y_k_l_m_n_o_p_r_s_t_u_v_h_ Fig. 40 PLATE XIII. A diagram showing the phases of the Moon. The Sun is at the top, with arrows pointing to "Direction of Sun". Below the Sun, there are four stages labeled "New", "First Quarter", "Last Quarter", and "Full Moon". Each stage shows a different phase of the Moon, with the Earth's shadow visible in the "Last Quarter" stage. The Phases of the Moon. 187 THE PHRASES OF THE MOON. 27 seems almost too commonplace to describe them in detail ; but something must be said on the subject. Let us first consider the phrase "New" Moon, which means that, after the Moon has completed one revolution round the Earth ending with its being lost in the Sun's rays, then, after passing through the first quarter of its disc, when it is still at a straight line, it emerges from the Sun's rays in the western sky in the evening. Each night thenceforward it gets farther and farther away from the Sun, and by day becomes more easily visible, until at last it is seen in the eastern sky. This is designated as "its First Quarter" (quois unum lunae), which means that half of the whole circle of its disc is illuminated, and it is then called "Full Moon," because the whole disc is illuminated and we see a complete circular area of light. The Moon is then on the meridian at midnight, and this is its most easterly position. A very important stage brings it, at the 28th of July, to its third, or as it is more commonly called, its "Last Quarter." It is then on the meridian at about 6 a.m., and remains so till about 6 p.m., when it is again distant (dependent on whether the season of the year is winter or summer) at or near the time when it is the ordinary breakfast-hour of the ordinary Englishman. At this time it is exactly distant from us in longitude and will be in conjunction with the Sun on or about the 28th day from which we started; that is to say, it will again be "New" at or near the time of midday. During this period of time, from New Moon to Full Moon, days it will be shining in broad daylight, and therefore more or less invisible, except that a good eye with a good telescope should be able to detect it. After Full Moon comes Last Quarter, without conjunction, being the 30 hours' interval already mentioned in a previous paragraph. [Fig. 40, Plate XI.]. The terms "New," "First Quarter," "Full," "Last Quarter," which have been made use of above are rather in the nature of fancy phrases, though everybody uses them, and they are 28 THE MOON. fairly well understood ; but, when employed in connection with the weather, are altogether illusory and meaningless. The special attractions of the Moon are its great size, its spectacular polar view, its mountainous and the other physical features of its surface, including those to which the names of " seas" and " walled plains" have been given. There are also certain characteristics of the Moon's appearance which are peculiar to it, and perhaps we should not be far wrong in regarding these as cracks in the lunar surface. The mountains, however, are the special feature of the Moon which has attracted the most recent and particular attention of the ordinary sightseer. It may be said that, as on the Earth, so on the Moon, the mountains are of two types : chains of mountains and isolated mountains. The former are named after rivers, lakes, seas, etc., by their own name, but the isolated mountains are of a twofold character—single peaks, and crater mountains, of which we have, on the Earth, only a few examples. The Earth has no craters comparable with the marked difference between the mountains of the Earth and the mountains of the Moon. Craters on the Earth are the exception, and very few in number ; craters on the Moon are numerous and very large. This is because on the Earth it is hardly putting the matter strong enough, because nearly the whole surface of the Moon is made up of crater formations. The fact that there are no craters on the Earth is perfectly clear that, at some past time, the whole surface, as we now see it, took its ultimate shape as the result of volcanic action. If anybody has any doubt about this the doubt must assuredly be dispelled by a comparison of the photographs of Fra Mauro Tenerife with that of any number of lunar peaks selected promiscuously. Of all principal lunar mountains have received names, chiefly those of men eminent in science, both ancient and modern. This system of nomenclature dates from the 17th century having been instituted by an Italian astronomer named Riccioli. FIG. 41 PLATE XIV. A lunar surface with various craters and maria. Plate XIV The Moon's Surface Modelled. By James Nasmyth, 1862. 28] Fig. 42 PLATE XV. The Lunar Mountain Copernicus (W. H. Pickering, photo). [2] DESCRIPTION OF THE MOON'S SURFACE. 29 In more recent times the greater number of the important mountains have been measured to ascertain their height above the general level of the Moon, above which some of them rise to an elevation of 20,000 ft. The work of measurement of heights was carried out on a large scale more than half a century ago by two German astronomers named Beer and Mädler, the value of whose labours has been universally recognised. The work is one of some importance, but its results are not very satisfactory as it is accomplished by taking observations under special circumstances of the angular dimensions of the shadows of the moon upon the Earth, and not upon the desired surface. The portions of the Moon's surface to which the name of "seas" has been applied were so called originally from their supposed nature; but it is now quite certain that there is no water on the Moon, and that these names refer to vast plains like the Steppes of Asia or the deserts of Africa. The seas have received very fanciful names, but, as they are connected with the sea of Serenity, they are all called seas. The result is not so irritating as when the English translation is employed. The following are some of the names: Mare Humorum, Mare Imbrium, Mare Nectaris, Mare Serenitatis, etc., etc. It would seem that we do not think to translate them, may pass muster; but how vapid they sound in their English forms: the Sea of Liqueids, the Sea of Snows, etc., etc. But let us call them the Sea of Serenity, the Sea of Tranquility—worthy of exact respect. A lunar crater usually consists of a sort of basin with a conical elevation rising from the centre, and a raised rim around it. The craters are often irregular in outline; those with a circular contour are rare; sometimes, however, a crater may be thought to be elliptical, but this is probably in most cases a perspective effect due to the foreshortening of the crater when seen from near the Moon's horizon. A verbal description of the appearance and structure of one 30 THE MOON. crater would move or less serve to describe every crater, and in real truth no vertical description is worth while; the craters must be seen either in profile, or in drawing, or through a telescope for the features, which all of them have more or less in common, to be properly realised. In describing the appearance of a telescope it is im- portant to bear in mind that it is only at the same period in each lunation—that is to say, at the same age of the Moon in days—that a crater may always look like this. The constant movement of the Moon away from the Earth, and the constant changes in the amount of sunshine falling on the Moon, makes the mountains present an incessantly varying appearance. The Sun is always shining upon one side of the Moon, but outside, the terminator (as the line dividing the illuminated from the unilluminated portion is called) the changes in question may often strike an observer, even from home to whom these types are familiar. In some cases the mountains are visible whilst the adjacent valleys are in shade; and the size and appearance of the tips are things always changing. At one moment two tips may be visible, at another they may be hidden; after a short interval a third will become visible; or, on the other hand, the two tips first seen may become invisible, whilst a new intermediate tip may appear. At this time of Fall Moon it is not much worth while looking at the Moon, so far as is desire to examine its formation in detail is concerned, because, the Sun then shining straight down upon it, it appears as a featureless expanse. On this account the Moon can best be studied at or near the Quarters, or when the Crescent Moon is sufficiently clear of clouds. When this crescent is full, it will continue to wax until it will fall to their maximum length on to the adjacent valleys and plains. Be it remembered, of course, that they will point in one direction when the Moon is waxing and in the contrary directions when it is waning. From the point of view of the general reader who only FIG. 43 PLATE XVI. A lunar crater with a large central peak and several smaller craters around it. The Mare Crisium on the Moon. From a Drawing by Professor L. Wernicke from a negative taken at the Lick Observatory. FIGS. 44-45 PLATE XVII. A close-up view of a lunar crater, showing its rim and interior. The crater appears to have a dark central area surrounded by lighter material. Aug. 17. Archibald, 1888. From drawings by Fred Whipple, enlarged for better viewing from negatives made at the Lick Observatory. 138 LIBRATIONS OF THE MOON. 31 aspires to be a sightseer there is not very much more to say with respect to the Moon. To the mathematical astronomer the Moon has given a great deal of trouble from time to time because its motions are exceedingly complex, and it can hardly be said, even now, that the subject has been thoroughly mastered. Speaking roughly, we may say that the whole hemisphere of the Moon is always turned towards the Earth; but this is not so exactly, for the Moon's axis of rotation is not perpendicularly oriented with the position of the Moon's axis with respect to the plane of its orbit, and the inclination of that plane to the Ecliptic, which is about 23° 27', varies slightly with time, like the Earth. Likewise, the Moon's angular velocity in its orbit is subject to a slight variation, in consequence of which a little more of its eastern or western edge is seen at one time than another. Moreover, on account of the diurnal rotation of the Earth, we view the Moon under somewhat different circumstances at different times of the year, according to the position of the place on the Earth at which we make our observation. These three foregoing sets of circumstances give rise to three kinds of libration in longitude, libration in latitude, and diurnal libration. The general effect of these librations is that, comparing one epoch with another, we see a narrow strip at one time and a wider one at another. This is true only approximately though we never see more than a complete hemisphere at one time, yet in the course of time we see all hemispheres, and a sort of surreptitious look round the corner. It is commonly stated that the Moon possesses no atmos- sphere, and this is in substance true; but very refined observa- tions have shown by means of spectroscopy that there is a very suggestive existence of an atmosphere so infinitesimally small that W. H. Pickering has put it at only $\frac{1}{10}$th that of the Earth. THE MOON. He says: "Although this value seems small, it is by no means insignificant, which would correspond to a pressure of hundreds of pounds per square inch on the surface of the Moon." Two expressions connected with the Moon may find a place here. The "Harvest Moon" and the "Hunter's Moon" are both of them well-known phrases more familiar however, to dwellers in the northern hemisphere than to dwellers towards the south. The Harvest Moon is that Full Moon which occurs nearest to the autumnal equinox. As the Moon then rises nearly at the same time every night, its visibility during the night is at the horizon almost opposite to the Sun, the duration of its visibility at night is about the maximum possible. The protracted moonlight is often very acceptable to the farmer at this season when his agricultural occupations cease. An old 18th-century writer on astronomy named Ferguson thus puts the matter: "The farmers gratefully ascribe the early rising of the Full Moon to the influence of the Sun, and they have long doubted that He had ordered it so on purpose to give them an immediate supply of moonlight after sunset for their greater convenience in expiring the fruits of the earth." The near coincidence in several successive risings of the Moon at this place is remarkable whenever our satellite is in the signs Pisces and Aries; but the phenomenon is only prominently noticeable when the Moon is "full" in those signs. It has been observed also that it coincides with the Sun in Virgo or Libra. The Harvest Moon is most useful when it is Full Moon about September 23. The Moon may rise as early as 6 o'clock in the morning, and as late as 10 o'clock in the evening, or even later than 10 minutes later each night. Under different circumstances--that is, when the Moon is in Libra, and at or near the descending node of its orbit--it may rise as much as 14 hours later one night than on the preceding night. The Full Moon next following the Harvest Moon is called LUNAR EFFECTS. 33 the "Hunter's Moon," and will usually fall in October. There does not attach to it the same glamour that attaches to the Harvest Moon, and it is spoken of much less frequently. It is to be presumed that it implies that the operations of hunting will commence at this moon, but at the time that this particular Moon displays itself in the heavens. There remains to be mentioned an interesting fact in con- nection with the light afforded by the Moon, namely, that we in the northern hemisphere see the Moon rise about two hours before (when it is most wanted) than we do in the summer (when we can most readily dispense with it). These differences in the times of rising are due to the fact that when the Moon is in the winter that the Moon is found in the most northern part of its orbit, because the Sun at the same time is exactly opposite to it in the most northern part of its (apparent) orbit. The Moon therefore rises earlier in the morning before and after the New Moon when there is the least possible amount of moonlight to lose. In the southern hemisphere, which is north of our Hemisphere, the reverse of all this is the case: the Moon's elevation above the horizon is the minimum possible, and the northern hemi- sphere of the Earth therefore receives the minimum amount of moonlight. The following quotation from a well-known book by a very well-known man brings under notice the Moon in quite a novel connection: "An evening was pleasant, and we dined in the open air. All the valley was very dark. The mountains showed a velvet black. Presently the moon rose. I repress the inclination to try and describe what I saw. The whole world was over- flooded with that mysterious light. All the suitable words have been used to describe it. It has been written over and skipped by countless readers. Indeed, I am inclined to think that these elaborate descriptions convey little to those who have not seen, and are unnecessary to those who have. Nature will not be blamed for giving us means of war, how-" 3 34 THE MOON. ever, especially of frontier war, the importance of the moon is brought home to everybody at every time does it rise-to-night? is the question that recurs; for other things--attacks, "sniping," rushes--besides the tides, are influenced by its movements." What is the amount of the light sent to us by the Moon? We buy and sell electric lamps calculated to display so much candlelight as may be necessary for any particular purpose with respect to the light of the Moon compared with that of the Sun? Such calculations have been made, but, as was to be expected, they have not been very satisfactory. In the century ago Rousseau calculated that the Moon's light was only one-fifth that of the Sun; several more modern estimations make it much less, and the only safe conclusion that one can submit is that the Moon's light is about one-tenth that of the Sun. It still hardly get the amount of daylight which we owe to the Sun. The question of the Moon influencing the weather on the Earth has already been alluded to, but something more must be said. People often remark in common speech, "Ah! the Moon changes to-morrow, and we shall have a change of weather." This is a very common expression. The first quarter Moon will be reaching its First Quarter, or Eastern Quadrature (to use the proper scientific term), the exclamation quoted is justified. But what happens when this Moon reaches its First Quarter? Its orbit goes away from the Sun, whatever has been the weather during the few days before the Moon reaches that point, that weather will be replaced by some other kind. It may be said, "But then why say that this is an influence?" In sense I will here quote the testimony of two experts on this subject. The late Astronomer Royal, Sir W. H. Christie, in 1870 said: "It seems doubtful whether the Moon has, or has not, any influence on the weather; but it is clear that, in any case, it can * W. S. Churchill, M.P., *The Malahand Field Book*, §27, p. 124. Figs. 46-51 PLATE XVIII. A small, irregularly shaped object with a central depression. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Rhabdomeres A larger, more complex structure with multiple protrusions and indentations. Rhabdomeres A smaller, more rounded structure with a central indentation. Figs. 32-37 PLATE NIX. Thallus. Gymnosporangium. Basidiospores on the Rote (Stromatophor). Basidiospores on the Rote (Stromatophor). Basidiospores on the Rote (Stromatophor). Basidiospores on the Rote (Stromatophor). 135 WEATHER NOT AFFECTED BY THE MOON. 35 have but very little influence, as such an influence has never been detected with certainty. The Moon's place is always in the sky, and its influence on the weather is only felt when the instants of change are 'new', 'full' and 'first' and 'last quarters'. If this pronouncement is not sufficiently emphatic, perhaps account somewhat similar one, taken from a letter from the Meteorological Office in London, may convince a Moon-believer: "No one in his senses can believe in the Moon's influence on the weather. The fact that storms move over the surface of the sea, and that the weather which suits the Moon in Ireland, it must fall to suit it in England." It is very remarkable how deeply ingrained in the minds of people is the idea that the Moon influences the weather, and that what are very improperly called "changes of the Moon" bring about, or are associated with changes in the weather. It is true that these changes do sometimes make a difference in the consequential result whether a so-called "change of the Moon" occurs at one particular hour rather than at another. In real life, however, they are not so much a cause as a circumstance which has no astronomical basis; and neither literally nor even figuratively has the slightest foundation in fact. Perhaps the situation may be best understood by considering what would happen if one express train travelling from London to Manchester without stopping at Rugby, and returning via Oxford without stopping at Birmingham? What if it passed through Rugby and Birmingham? Notwithstanding what I have said above, there are a few genuine weather signs which, it may be admitted, are associated with the Moon, but have no physical connection with it. For instance, if the Moon looks pale and the horns blunt, or lack 36 THE MOON. sharpeness, rain is indicated ; but if the Moon is clear and sharp, and also bright, so to speak, it is a sign of fine weather which is likely to continue. But when the Moon is dark and cloudy, we may say that it is a sign of bad weather. It often happens that when the Moon is two or three days old the dim outline of the portion not directly illuminated by the Sun can be seen, shining with a pale grey light. This appearance is called "the Moon's arms," though it would be better to put it in the other way about and call it "the Old Moon in the New Moon's arms." The appearance of this sign is due to the fact that the Moon has lost its brightness through the clearness of distant hills, which clearness is an almost invariable forerunner of rain. It is sometimes suggested that the question of the effective meaning of this sign depends upon the position of the Moon at the time. For instance, if it is exactly horizontal or an inclined position; but nothing depends on this, because the position as regards level of the line joining the horns of the Moon does not depend upon the season of the year as regards the place of the Moon in the sky. This will be seen from what I have said respecting the Sum. [PLATE XXI.] When the Moon is nearly full, either before or after, it frequently appears that when the clouds rise in the sky on a clear night, the clouds break up and disperse as the night wears on. I regard this as a well-authenticated fact, which I observed myself many years ago. I have written a poem on this subject, and also put it in print, and I may add that I have often noticed it myself since, though Mr. W. Ellis, late of the Greenwich Observatory, has pointed out to me that he had never noticed such a phenomenon before. He has also expressed the idea that the Moon imparts a certain very faint amount of warmth to the Earth, as the direct observations of the late Earl of Rosse distinctly indicate. Subject to the foregoing exceptions, it may be said that the following composition of some unknown "poet" (save the mark;) Plate XX Fig. 58-63 Photograph of a lunar surface with craters and maria. Photograph. Photograph of a lunar surface with craters and maria. Photograph. Photograph of a lunar surface with craters and maria. Photograph. Photograph of a lunar surface with craters and maria. Photograph. s8j Mountains on the Moon (Stromatolites). Canyons. Extract. Figs. 64-67 PLATE XXI. Atlas and Bercozor. The Apennine. Alphonsus. Aristarchus. Mountains on the Moon (Stuyvesant). 38 POPULAR DELUSIONS. 37 correctly represents the facts as regards the Moon and the weather: "The Moon and the weather Are very different things; But change of the Moon Does not change the weather; If we do not believe this, And that may seem strange— We shall be wrong still! That's subject to change." Besides the question of terrestrial weather, the Moon is credited with other influences, some genuine ; some perhaps genuine, but more likely mythical. The most genuine lunar influence is its effect on the tides of the sea. This is a matter of immense importance, and deserves a separate chapter hereafter. The influence which I have described as perhaps genuine is one which is wholly independent of the so-called changes of the Moon. It is the increase of the Moon from New to Full, and during the increase of the Moon from New to Full towards Full than from Full to towards New. Moreover, that when the Moon is in perigee, or nearest the Earth, the chances of great storms are increased from those away from the Earth. Contrary to the prejudices of most people, perhaps only one in ten believes that the period of New Moon is the period when changes of weather may be lost looked for. The alleged lunar influences which must be regarded as such are those which are attributed to the Moon. One of these is that which is enshrined in the word lunatic, which philosophically may be taken to imply that the Moon has something to do with people going out of their minds; but, although this idea has been popularized in books by writers of which insinuate that the rays of the Moon exercise a mischievous influence on human beings exposed to them. This is especially an idea current in the East, though it finds a 38 THE MOON. counterpart in ideas met with nearer home. A writer named Carne has remarked— "The effect of the Moonlight on the eyes in Eastern Coun- tries is singularly injurious. The natives tell you always to cover your eyes when you sleep, lest the light of the sight of a person who should sleep with his face exposed to the Moon at night would soon be utterly impaired and destroyed." Another writer, named Anderson, speaking of Bavaria, is still more thrilling in his language:— "One must here take great care not to sleep in the beams of the Moon. I have seen many persons whose necks have become crooked, so that they look more to the side than forward." A writer of very ancient date, Plutarch, remarked that the light of the Moon causes animals substances to putrefy; and it is said that Sicilian fishermen cover during the night fish which they expose on the shore-to dry, and for the same reason. Even in our own country, when the Moon is full, and the descent of Aeneas into Hades, speaks of the incertum Lunam sub luce muliiget," the Moon's doablest and malignant light." The old forest laws of France forbade the falling of trees except during the first three days after the new moon. In 1750, ago, that stated peat dug during the increase of the Moon continues moist and never burns clear. The writers of a very well-known book make the following statement: "Lunar influence seems to occasion phenomena of a very curious nature. It is confidently affirmed that it is not unusual for men on board a ship while lying in the moonlight, to feel themselves inclined to lie down. This is called by some the translation of "mulagust" for seagulls; but Valpy renders it " faint and glistening," which wholly changes the sense." The "Lunar Influence Round the World," by the Rev. D. Tyerman, and G. Bennett. A page from a book with text about lunar influences. STATISTICS. 39 their faces exposed to the beams, to have their muscles spasmodically distorted and their mouths drawn away—affections which may be fatal, and which are often so severe as to injure in their sight as to lose it for several months. Fish, when taken from the sea-water, and hung up in the light of the Moon, are often found to have their eyes so affected that, when eaten the next day, the infected food has produced symptoms of insanity in those who ate it. This is particularly true with people who have been themselves disordered after having partaken of such fish. It is hazardous to touch on this subject ; but I am convinced that it is a fact worthy of being believed, and who would not affirm that of which they themselves were not perverted." There is a circumstance, an element of good faith in the foregoing statement, which makes it impossible to disbelieve the facts stated. But where the writers have gone astray, and others have gone astray with them, is in their erroneous explana-tion of the cause of the phenomenon. The Moon is not this. Animal substances may seem to putrefy, and peut to be destroyed by heat; but it is impossible for human beings to become subject to bodily ailments when exposed to the light of the Moon, nor because of that light, but because of its effect upon the atmosphere (which is clear to permit a full display of moonshine), the radiation of heat from the Earth's surface is facilitated, so that objects, whether animate or inanimate, are heated more than usual; and the deposition of dew is therefore facilitated, and it is the moisture thus engendered which hastens the development of muscular pains and bodily ailments in animated beings, and decreases the strength of inanimate things. The Moon travels round the Earth in 27 days, 7 hours, 43 minutes at a mean distance of 237,500 miles. Owing to the fact that she revolves in a circle but does not move in the direction of which it is 0° 51', it may sometimes be as near to the Earth as it is 226,000 miles, or may recede to as far as 235,000 miles. In consequence of this eccentricity its apparent diameter may vary between 29' 28" and 33' 3". Its diameter at mean distance is THE MOON 31' 5" and its true diameter is about 2,160 miles. It will be sufficiently near the truth, for popular purposes, to say that its diameter as we see it is about 3", and is therefore about the same as the diameter of the Sun. But owing to the influence of the Earth's atmosphere the apparent diameter will differ somewhat according as we view the Moon when high up in the sky or low down near the horizon; CHAPTER IV. THE TIDES. The tides matter of interest to the inhabitants of maritime countries— Influence of the Sun on the tides—The Moon's influence on this influence—that of the Moon greatly predominates—Spring Tides— Neap Tides—the difference between them—The tides of the port—"Promising" and "Lagging"—of the tides—Emotional tide—The tide of the sea—The tide of the land—The tide of —in and around Great Britain.—Amongst the South Sea Islands— Influence of the tides on commerce—Journey of the tides round the Earth—the "Bore." THE subject of The Tides of the Ocean is a mixed astronomical and geographical one, and it comes so much home to the inhabitants of these United Kingdoms that Great Britain and Ireland that it must not be omitted from a volume which appeals to those interested in studying things which they can see. And it follows naturally chapters devoted to the Sun and Moon, since these two luminaries are jointly concerned in causing the tides. Diagrams illustrating the theory of the tides appear in every book on astronomy, but it is only when we come to deal with scientific problems that diagrams become necessary. As happens, it is possible to explain the matter without diagrams, which is a thing not always possible in dealing with some scientific problems. Let us consider, at all, the case of the Moon. The Moon is the Earth's satellite, and as such is primarily responsible for the tides, though, as we shall see presently, the Sun is also concerned in a lesser degree. 41 THE TIDES. The Moon, being the Earth's satellite, is in a sense held in its place by the attraction of the Sun; but there is a certain amount of mutuality in the latter—that is to say, though the Earth attracts the Moon, the Moon has a slight attractive power on the Earth, but it does not suffice to do much more than attract the Earth towards itself. This is only half the truth, for the Moon does draw the Earth to a slight extent ; but in doing so the water on exactly the opposite side of the Earth is drawn up. It is true that, whilst it is high-water when the Moon is on, or near the meridian of the place of observation, there is also a condition of high-water on the opposite side of the Earth at about 12 hours later. This is spoken of as coincident tides spoken of. In other words, the coincident tides are separated from each other by 180°, or by half the circumference of the Earth. The cause of this separation is due to the rotation of the Earth thus causes the tidal waves to pass successively right round the Earth once in about every 24 hours it follows that as there are two tidal waves constantly in motion, there are everywhere two high-tides daily, with an interval of about 12 hours between them. Now let us consider the influence of the Sun as brought into action by its attraction upon the waters. Since its mass is greater than the mass of the Earth, there are two reasons why the power of the Sun to raise or develop tides on the Earth is much less than its preponderating mass would lead us to suppose. First, because it is situated at a great distance from the Earth, compared with the distance of the Moon from the Earth, diminishes the power of the Sun compared with what it would be if it were nearer. Secondly, since it takes a long time for development of the tide is due solely to the inequality of the attractions in operation on different sides of the Earth, so that the greater the inequality the greater the resulting tide and vice versa. The mean distance of the Sun from the Earth is about 17,730 diameters of the Earth, and consequently THE THEORY OF THE TIDES. difference between the distance of the Sun from one side of the Earth compared with the other will be only $\frac{1}{30}$th of the whole distance, and therefore the difference in the mean distance is only 30 per cent of the Earth's, the difference between the distance from one side compared with the distance on the other side will be 45th of the whole distance. Under these circumstances, which are very simple, depends on the inequality of the attraction and the inequality being in the case of the Moon represented by $y$, whilst in the case of Newton's theory it is only $\frac{1}{30}y$ that is represented by $x$. The reason why this inequality exists in the case of the Moon is because the other is obliquely worked out mathematically it was calculated by Newton to be about 24 to 1. Tides far we have been supposing the Sun and Moon to be pulling together, but they only do that when they are in the same straight line, which is when the Moon is what we call New Moon. But when they are at right angles to each other, i.e., $\frac{1}{3}$th of the way round in its orbit, reckoned from the stage known as New or Full, then Sun and Moon do not pull together, and the resulting tide is only that due to the surplus influence of one body over another. This surplus influence being so small, the resulting tide is a much smaller one than when they pull together. This explains the contrast which all residents on the coast observe between high and low water marks which they observe at the epochs of New and Full Moon compared with the rise and fall of the tides at the Quarters. The former tides go by the name of "spring tides" because they are said to spring up from their respective high-water and low-water marks respectively. The latter are known as "neap tides", and result in only a moderately high- or low-water mark. The cause of these two kinds of tides is that any change in cause of these last-named circumstances will now be easily understood, for, whilst Spring Tides depend upon Sun, Moon, and Earth being all the same straight line, in the Neap Tides the Moon's attraction acts along a line perpendicular to that of 44 THE TIDES. The Sun, in other words, the two bodies partly neutralise one another's action. All the foregoing remarks have been based on the assump- tion (which is baseless), namely, that the Earth is a sphere covered all over by a layer of water of uniform depth ; but it is impossible to make any experiment on this assumption, in order to make the matter more easily comprehensible, and for the same reason the following propositions are framed on the same supposition, to be modified by subsequent explanations. 1. The Sun rises at noon, and sets at midnight, passes the meridian at the same time, namely, at noon ; then, after an interval, high-water occurs. Then the water begins to fall for 6 hours, and rises again for 6 hours ; then falls for 6 hours, rises for 6 hours, and so on. Thus, when it rises for 6 hours 12 minutes to a second maximum ; then falls for another interval of 6 hours 12 minutes, and rises again during a fourth interval of 6 hours 12 minutes. It has, there- fore, risen twice in 24 hours, and fallen twice in 24 hours, 48 minutes, which is called a "tidal day." The foregoing intervals are not quite correctly expressed, even in theory, for the water usually takes a longer time in falling than it does in rising ; but this difference is very small compared with what we shall see. 2. On the day of Full Moon the Moon crosses the meridian 12 hours after the Sun, namely, at midnight, and the tidal phenomena are the same as stated in the previous paragraph. 3. As time is reckoned by the apparent motion of the Sun, the Moon appears to move through the heavens in one place ; but the lunar tide, which is the greater, and therefore gives a character to the whole, happens 48 minutes later every month. For instance, if there is a lunar spring-tide at that rate, and becomes later and later till, at the First and Third Quarters of the Moon, it happens at the same time I ignore here the question of the difference between apparent solar time and mean solar time and the customary adjustment of these times by what is called the almanacks—the "equation of time." A diagram showing the phases of the Moon and its effect on tides. **DETAILS AS TO THE TIDES.** as the low-water of the solar tide : then the elevation of the high-water and the depression of the low will be the difference of the two tides, and the general condition of these will be represented by the term Neap Tide. 4. The difference in height between high and low-water is called the "range of the tide," and obviously may be measured in feet or inches, according to the scale of the chart. It is usual to place a post of suitable height, and suitably placed for the purpose. The former principle of measurement would be the one adopted by Captain Cook, who stated that "the range of the tide was but the least part often be noticed as measurable by numbrers." This is true, as on the chart supporting a pier, or painted on the upright wall of a jetty or breakwater. 5. The Spring Tides are the highest, especially those which happen 36 hours after the New or Full Moon. The Neap Tides are the lowest, especially those which happen 48 hours after the New or Full Moon. 6. The time of day when the Moon is at one of its quarters, or in quadrature, to speak scientifically. 7. The interval of time between noon and the time of high water at any particular place is the same on the days both of New and Full Moon. This fact is well known to all who have seen at any place when the Moon is New or Full call is made by French writers L'Établissement du port, and that expression has now become proverbial in English as "L'Établissement du Port," an awkward phrase which is not worth more than no meaning till explained. This fact that an interval of time elapses at any given place between the meridian passage of the Moon and the time of high-water is due to another fact, namely, that the waters of the ocean are retarded by friction whilst they are in motion towards their destination. This retardation is caused by friction between both the lunar and the solar tidal waves are not found immediately under their respective luminaries, but follow them at a certain distance. Moreover, the tidal wave is affected in another way by the action of both these luminaries, and at certain periods 45 46 THE TIDES. of the lunar month the progress is either accelerated or retarded. During the First and Third Quarters the solar tide is W., of the lunar one, and the combined effect of the actual high-water due to the combination of the two waves will be to the W. of the place at which it would have been if the Moon were acting alone. The combined effect of the two tides will be to the E. On the other hand, in the Second and Fourth Quarters the Sun produces a retardation in the time of high-water. These effects are called the "priming" and "lagging" of the tides, and the effect of these two tides on each other is such that a value of 48 minutes may be augmented to 60 minutes or be reduced to 36 minutes. It follows from this that a sea-bathing bath cannot be taken on a day when the Sun is in his foot-hood, and on a certain day does just escape the stones, will not of necessity on the next day find himself exactly in the same pleasant position at an instant which is exactly 48 minutes different from the time shown by his watch on the previous day. The highest Spring Tides occur when the Moon passes the meridian at its greatest declination, and coincides with the Sun, for then the maximum effects of the two luminaries coincide. The height of the tides is affected by another consideration—positions of the Moon and the Sun with respect to the Equator; the nearer these two bodies are to the Equator the greater the height of the tide. Twice a year, at what we call the Equinoctial Spring Tides, both bodies are in their most speaking roughly—the Sun is actually in the Equator. If at these dates the Moon should be in or near the Equator the tidal height will be at its maximum. This occurs twice a year as at the Equinoctial Spring Tides. On the other hand the smallest tides will occur at about the Solstices (June 21 and December 22) if the Moon attains its least or greatest meridian height at the same time as the Sun. Finally, the distances of the Earth from the Moon and the **DETAILS OF THE TIDES.** 47 Sun also affect the height of the tides. Other things being equal, the height of a tide is greater or less according as the Sun and the Moon are near to or far from the Earth. According to this, the Sun is nearer to the Earth at high tides than those at or near June 21, the Earth being nearest to the Sun (perigee being in January) and farthest from the Sun in August. Thus far in our consideration of the tidal wave we have been keeping up the fiction, already referred to, of the Earth being everywhere covered with water of even depth everywhere. It needs not to be pointed out that this is pure fiction, some parts of the Earth being land and other parts being water, the sea being unevenly distributed over the surface of the Ocean everywhere being of varying depth, just as the elevation of the land is everywhere of varying height. It is evident that this influence on the times and circumstances of the movements of the Earth's water; and though the rotation of the Earth on its axis and the movements of the Moon and of the Sun all co-operate to produce tides, yet it is only by reason of the unevenness of water which exist on the Earth, local circumstances entirely destroy the theoretical conditions. In other words, the actual cause of tides is not found in any one thing, but is incapable of being defined by cast-iron rules because of the irregular outline of the land, the uneven surface of the bed of the ocean, and the action of winds and of currents of air over water, and so forth. The effect of all these disturbing influences cannot be better brought home to the mind than by a consideration of the following diagram. The whole area represented by a circle covered by the hypothetical layer of water mentioned on a previous page, the height of a tide raised by the Sun's attraction would be $f$ ft. in., and of a lunar tide $a$, ft.; but the difference in the level of the waters in the ocean due to the 48 THE TIDES. disturbing causes just spokes of fire, in the vast number of cases, entirely different, and in excess of these figures. In deep estuaries or creeks ending in narrow channels, which gradually converge inwards as a common wine-annex, does the range, very much greater than along an open shore. For instance, at the mouth of the River Thames, the range of rise and fall is as much as 38 ft., and in some similar situations in foreign countries the range is even greater. I have examined the tide-gates at the mouth of the Bristol Channel on the Gloucester side of Chepstow, and the rapidity with which landmarks such as piles and rocks, near and around which I had walked a few minutes previously, were submerged by the rising water, and raised again by the falling tide, shows that the experience of the rise and fall of the tides was limited to open shores on the South and East of England. Along the coasts of Europe, where they are in feet, are comparatively limited, especially where promontories or headlands jut out into the sea. Thus, at the Needles in the Isle of Wight, the range is only 9 ft., whilst at Weymouth it is 10 ft., and at Portland 11 ft. The same is true of large open expanses of water such as the Atlantic and Pacific Oceans, and confined seas like the Mediterranean, the elevation of the tide being measured by its height above beaches rather than by feet. Thus at Toulon it is 1 ft.; at St. Helena 5 ft. The barometric pressure of the atmosphere is also a factor to be taken into account in considering the probable range of the tide. This has been shown by a great many writers. When this barometer is low an unusually high tide may be expected, and vice versa; and it has been estimated that a depression of 10 mm. will cause a rise of 6 inches in the tide at London Docks the effect of raising the level of the tidal water by the amount of 7 in., which at Liverpool would be 10 in. Thus it would come about that, supposing an unusual high tide to occur (as it happens) brought about by a fall so low to the level of the harbour of the Thames Embankment, a AENORMAL TIDES. 49 sudden fall of the barometer might unexpectedly bring the water over to the highway, though no such risk had been taken by the constructors of the road. The barometer alone cannot be left out of account, for it is often very potential either in aggravating the destructive effects of a very high tide or of checking them. The Pacific Ocean and among the South Sea Islands that the most extraordinary anomalies in connection with the tides are to be observed. Many travellers and navigators who have visited these islands, and who have recorded their strange experiences, I have come across many such records, and transcribe the following as the most recent which I have seen. I am aware that where I live, at [Tahiti] where the tide is high but once a day, and regularly at the same hour between 1 and 2 o'clock in the afternoon. The sun rises at 5 o'clock, and sets at 7 o'clock; therefore, a corresponding movement of the sea after midday. It renders it imperceptible to those who do not observe regular evening breezes returning and setting in the morning. I have asked many questions on the subject, but I have not been able to elicit any thing more than vague conjectures. There is nothing in the sailing instructions issued by the Hydrographic Department, do more than chronicle the extraordinary fact, The following description of the course of the general tidal wave of the Earth is so clear and concise that it can neither be improved upon nor be abridged. I therefore quote it in full. "The Atlantic is the cradle of tides. It is here that the Sun and Moon exert their influence. They are not only active, but they are, so to speak, to attend on the guidance of their own congenital tendencies. The luminaries continue to travel round us, but we are so far removed from them that they no longer follow them. The Atlantic, for example, opens to E. REEVES, Brown Men and Women; or, the South Sea Islands, p. 301, London: 1860. 4 50 THE TIDES. them a long, deep canal, running from north to south, and after the great tidal effect has entered the mouth of this Atlantic canal it moves continually northward ; for the second 12 hours of its life it travels north to the Cape of Good Hope, and then turns round to the eastward, and at right angles to its existence has brought high-water to Cape Blanco on the western coast of South America, and low-water to the same place. Turning now round to the eastward, and at right angles to its original direction, this great tidal wave brings high-water, distinctly marked by a line of white foam, along the coasts of Ireland and England. Passing round the northern cape of Africa, it comes into the Mediterranean Sea, and then also to the opposite coasts of Norway and Denmark. It has now been travelling precisely in the opposite direction to that which it took before, and consequently it is now in the same position with respect to the motion of the Sun and Moon. But its erratic course is not yet complete. It still continues to travel northward, though the German Ocean southwards. At midnight of the second day it is at the mouth of the Thames, and wafts the merchandise of London towards the North Sea. The reader will find a description of this rapid journey the reader will have noticed how the lines (on page 37) show that there is a difference between each other, while in others they are wide asunder. This indicates that the tide-wave is travelling with varying velocity. According to this view, it would take about two hours to go from one hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through the Atlantic scarcely less ; but near some of the principal cities of Europe it may take more than an hour, and through TIDES ON THE ENGLISH COAST. 51 Earth would be rather more than 1000 miles per hour, and the writer of the foregoing extract seems to think that this velocity is reasonable. But, on the contrary, it appears there exists a vast stretch of water not broken in upon by any important masses of land. Therefore, when we mention the islands of the Pacific as localities where special anomalies exist in connection with the tides, it must not be forgotten that much nearer home, to wit on the coasts of Hampshire and the Isle of Wight and some parts of the south coast of England, the same condition of thing tidal are often exhibited. In the case of Hamp- shire, owing to the fact that the tides in the Solent and at Spithead do not run eastward, the flood and ebbtony on the isles, as it is called, in the open Channel run from— Half-flood to half-ebb—eastward, Half-flood to half-flood—westward— Southampton and places up Southampton Water have four tides in the 24 hours instead of two, so that, after flowing to the north-eastern part of the Solent, they turn back again to tide changes outside Calshot Castle, there is a slack and a partial ebb, until the eastern tide brings enough water to push the flood home to its full. Likewise on the ebb, when the tide turns back towards Southampton Water, there is a continuation of the west-going tide draws the water away down Channel. The situation of the Isle of Wight as an island opposite an estuary like Southampton Water suggest that similar tidal vagaries exist elsewhere in the world. As regards anomalies elsewhere in the British Isles, it is remarkable how little attention has been paid to them under geographical circumstances of the West of Scotland that in the strait between the island of Isle and the islets of Chenzie and I owe the foregoing account of the tides in the Solent to Mr. C. G. Brodie, F.R.S., an experienced yachtsman, and I have never seen this information in print. §3 THE TIDES. Ours the time occupied by the ebb-tide out of the theoretical 12 hours is 10½ hours, whilst the flood-tide occupies only 1½ hours. The last matter to be mentioned in connection with the tides is the striking and remarkable phenomenon which, bearing various names, has been observed in England and France. It is to be seen only at the mouths of rivers which contract at a sharp angle from wide to narrow, carrying, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel, carry, as it were, up the estuary into the main channel. From this point on I have borne on my way to China. In China must be regarded as one of the most remarkable in the world; and there is the further fact attaching to it that it has been made subject of a very full and complete scientific investigation. The account of this was given by Admiral W. U. Mooree whose account was communicated in 1889 to the Institution of Civil Engineers. His remarks are so interesting that I think I shall make my account of bores in general much more complete than could otherwise have been [Footnote: P. XIX.]. To begin with the name "bore". The Admiralty uses it to signify a wave or a current. The word bore is also called in England "the hygge" and "the eage"; also "the eage". The Admiralty derives "eage" from the French "eau-queue", or "eau-queue". In France it is known as "la mascarete", and in Brazil as "the pororoca". It seems to occur in 6 or 7 rivers in the British Isles; including the Severn, the Wye, the Trent; and some of those in France; such as those of Dordogne and Garonne; and in some of the Indian rivers; including the Ganges; Brahmaputra and India's; in branches which compose mouth of Amazon River; S. America; and in one river in South Africa. It is rarely observed except at a spring tide; and as a rule shows itself THE "BORE." 53 on the days of Full and New Moon, appearing with the first of every flood-side for 3 or 4 days succeeding those phases ; after which the tide continues only a swift rush unaccompanied by noise or violent commotion. The following conditions appear to be necessary to create a bore. 1. A swiftly flowing river. 2. An extensive bar of sand, dry at low-water, except in certain narrow channels kept open by the outgoing stream. If these two conditions are fulfilled, the water must be funnel-shaped, with a wide mouth which is open to receive the tidal wave coming in from the Ocean. If either of these conditions is lacking there will be no bore. For example, in the case of the Thames, the third condition exists, but the first and second are wanting; for the Thames is not a swift river, and has no bar, dry at low-water. In the case of the Severn, the first condition is wanting; there is a bore; not a very large one, it is true, but still the most noteworthy in the British Isles. The Severn estuary, therefore, has all 3 conditions well developed. The estuary into which the river falls has a vast area of sand at its head, and is favourably situated for the reception of the incoming 'tidal wave' from the Pacific. The mouth of the estuary is formed by the long Channel Gulf; it is 12 ft., but as the wave becomes compressed in advancing towards its head at the end of the navigable waters, it is as much as 60 ft. wide. This compression of the wave thus gives the favourable combination of a wind blowing on shore, and a Moon in perigee at the time of Full or New. The navigable breadth of this estuary is about 10 miles; so that when (at its greatest height) is about 1th or 1th of what it is at the mouth; and if there were no river discharging into the bay the range would probably be 60 ft. or 70 ft., as in the Bay of Fundy. The speed of the advancing tidal wave was measured by the THE TIDES. officers of H.M.S. *Rambler*, and found to be 744 statute miles an hour. The breadth of the bore is about 1 mile, and its front presents the appearance of a gleaming white cascade of foaming bubble, 8 ft. to 12 ft. in height. The noise is not the least impressive feature of this phenomenon. On a calm still night, the sound may be heard at a distance of more than an hour before it arrives. The noise increases very gradually until the bore comes abreast of an observer on the bank, and then it ceases abruptly after a year but little inferior to that of the Rapids below Niagara.¹ South America seems to offer an example of a bore of a very remarkable character. The following description of a bore on the River Plate, near Montevideo, La Conception, a great many years ago is a fitting pendant to Admiral Moore's account of the Tsien-Tang-Kiang bore: "During three days before the New and Full Moons, the period of the highest tides, the sea, instead of occupying six hours only, occupies ten hours, sometimes even twelve or two minutes. The noise of this terrible flood is heard five or six times during each day. In the middle of the night we see a liquid promontory 12 or 15 feet high, followed by another, and another, and sometimes by a fourth. These waves are so rapid that they seem to be thrown up by a machine with a prodigious rapidity, rending and crushing everything in their path. The whole tract of land is swept away by it, and sometimes whole tracts of land are swept away." ² Abridged and added to from Admiral Moore's paper in the *Minutes of Proceedings* of the Royal Society of Canada, vol. xxxvii., p. 360-361. ³ Part I. A will more detailed account will be found in the Journal of the British Association for the Advancement of Science, vol. xxii., 1886. See also Sir G.H. Darwin's "Tide-Power," &c. A diagram showing a tidal bore. CHAPTER V. THE PLANETS GENERALLY. What the planets are—Man be conveniently divided into two groups—the Inferior Planets—the Superior Planets—the Minor Planets. Certain planets have phases—the planets in Conjunction—the planets in Opposition—the planets in Retrogradation—common to all the planets—Statement of these by Hindu—Kepler's Three Laws—Instances of this—Various discarded planetary systems. Suggested Intro-Mercurial and Trans-Neptunian planets. ROUND the Sun, as a centre, there circulate a considerable number of bodies, which we know to be, indeed, many hundreds in number, but we can count on our fingers those which alone are worthy of general attention. Those which are known to everybody and which are most frequently mentioned at present time are still fewer in number, and comprise only Mercury, Venus, the Earth, Mars, Jupiter, and Saturn. For the purposes of astronomy, however, the word planet has a very proper sense of the word, may be left out of consideration, because we, being on the Earth, cannot approach its study in the same way as we do that of the other planets. The study of the Earth concerns the sciences of geography and geology in particular, and, except for the purpose of noting its place in the solar system, because it is one of the coregide * Greek, wanderer. 53 56 THE PLANETS GENERALLY. planets which travel round the Sun, the astronomer has not much concern with it. He uses it, however, for the arbitrary purpose of separating the planets into two groups, putting into one group those which are nearer the Sun than the Earth and into the second group all the other planets outside the orbit of the Earth. The former are called " Inferior" planets, and so, far as we know, they are always smaller than the Earth. The latter, on the other hand, are called " Superior" planets, and include not only the other three named above (Mars, Jupiter, and Saturn), but two other large planets still farther off, Uranus and Neptune, together with a number of others which are very small indeed, such as " Minor" planets, which circle round the Sun in orbits lying between Mars and Jupiter. It is well to remember, from what has just been said, that the designations " Inferior" and " Superior" are not a little misleading, because both the Inferior planets are very much larger than nearly all the Superior ones, reckoned in respect of their diameters. There is another important distinction between the two classes of planets. The Inferior ones have no satellites, whilst all the Superior ones do possess them. These satellites are bodies which are called satellites, though frequently spoken of as " moons," because serving the purposes served by our Moon. This distinction regarding satellites is of great importance, and its explanation may possibly be assigned to designs on the part of the Creator. Mercury and Venus, being so comparatively near to the Sun, do not need the benefit afforded by a satellite in supplying them with light. On the other hand, Mars and Jupiter, being more distant from the Sun, is so favoured by having a companion to afford additional light, and probably it may be said with truth that, as all the other Inferior planets have satellites, and with this exception of Neptune, satellites generally supply光light to all other Earths, such satellites may be regarded as performing the special office of supplying in some degree to their primaries light by way
56 THE PLANETS GENERALLY.
planets which travel round the Sun, the astronomer has not much concern with it. He uses it, however, for the arbitrary purpose of separating the planets into two groups, putting into one group those which are nearer the Sun than the Earth and into the second group all the other planets outside the orbit of the Earth.
The former are called " Inferior" planets, and so, far as we know, they are always smaller than the Earth. The latter, on the other hand, are called " Superior" planets, and include not only the other three named above (Mars, Jupiter, and Saturn), but two other large planets still farther off, Uranus and Neptune, together with a number of others which are very small indeed, such as " Minor" planets, which circle round the Sun in orbits lying between Mars and Jupiter.
It is well to remember, from what has just been said, that the designations " Inferior" and " Superior" are not a little misleading, because both the Inferior planets are very much larger than nearly all the Superior ones, reckoned in respect of their diameters.
There is another important distinction between the two classes of planets. The Inferior ones have no satellites, whilst all the Superior ones do possess them. These satellites are bodies which are called satellites, though frequently spoken of as " moons," because serving the purposes served by our Moon.
This distinction regarding satellites is of great importance, and its explanation may possibly be assigned to designs on the part of the Creator. Mercury and Venus, being so comparatively near to the Sun, do not need the benefit afforded by a satellite in supplying them with light. On the other hand, Mars and Jupiter, being more distant from the Sun,
is so favoured by having a companion to afford additional light,
and probably it may be said with truth that,
as all the other Inferior planets have satellites,
and with this exception of Neptune,
satellites generally supply光light to all other Earths,
such satellites may be regarded as performing
the special office of supplying in some degree to their primaries light by way
MOVEMENTS OF THE PLANETS. 57 of compensation for the limited amount of Sunlight which they receive because of their vast distance from the Sun. There are another two classes of planets, viz., the Superior and Superior Planets. The former are subject to phases which are identical in character with the phases of the Moon—Crescents, Quarters, Full, and so on; whilst the Superior Planet Mercury and Venus (which have only a slight degree), exhibit no appreciable phases. The phases of Mercury and Venus involve the consequence that when these planets appear on this side of the Sun looked at from the Earth, and sometimes on the farther side of the Sun. When passing on our side, then, at the moment at which Earth, planet, and Sun are exactly in the straight line, we see them in conjunction with the Sun. When on the opposite side, with the Earth, Sun and planet in the same straight line, the planet is said to be in opposition with the Sun. In both these cases, however, there is when in these two positions (and also, unless they are at a certain distance, on either side) the planets will be lost in the Sun's rays, and will therefore be invisible to us. This phenomenon is called "Conjunction," and that of being visible when in opposition is called "Opposition." The phenomenon, which is rare, constitutes what is called a "transit" of the planet. But the consideration of this in detail belongs to a later chapter. The circumstances of the Superior Planets are altogether different. They never can be in Conjunction with the Sun in the same sense that the Interior Planets can, because they are always too far away from it to be seen by us through the Earth. The epoch of Conjunction with them puts them in a straight line but in a different order, namely, in the order of Earth, Sun, Planet. When this happens they are invisible from the Earth because lost in the Sun's rays ; and that state of things subsists A diagram showing the relative positions of Earth, Sun, and various planets. 58 THE PLANETS GENERALLY. for a certain length of time before and after Conjunction, dependent on the brilliancy of the particular planet and our optical means to view it when immersed to some degree in the Sun's rays, which means in some degree of twilight. The Superior Planets are also on occasions in Opposition, but have no visible phase, because they are too far away as it has when applied to an Inferior Planet. An Inferior Planet is, as we have seen, lost in the Sun's rays ; but a Superior Planet is visible at all times, being always in Opposition, because it is on the meridian at midnight when the Sun is on the meridian at midday, the order of position being Sun, Earth, Planet. It is only the Inferior Planet subject to a clearly evident phase is Mars, which in two positions in its orbit (Quadratures, E. and W.) suffers a slight enroachment first on one side and then on the other. In this case, however, Jupiter should exhibit a slight phase under analogous conditions, but it is not very easy to appreciate it; still, it must be deemed, when at its quadrature, to be slightly greater (as the term is), but not so much as the manifestation of light is on the limb of the planet which is farthest from the Sun. There are certain characteristics common to all the planets, which are worthy of notice. First, their motions are: 1. They move in the same apparent direction round the Sun, their course, as viewed from the N. side of the Ecliptic, being contrary to the motion of the hands of a watch. 2. They describe oval or elliptical paths round the Sun, not however, differing greatly from circles. 3. They are either within or without the Ecliptic, and intersect it in two points, which are the "Nodes," one half of the orbit lying N. and the other half S. of the Earth's path. 4. They are opaque bodies, like the Earth, and shine by reflection; that is why they receive light from us. 5. They revolve upon their axes in the same way as the THE ORBITS OF THE PLANETS. 59 Earth. This, we know by telescopic observation, to be the case with many planets, that are known to us, their days may be extended to all. Hence they will have the same duration during day and night, like the inhabitants of the Earth ; but their days are of different lengths. 6. Agreeably to the principles of Gravitation, the planets move at those parts of their orbits which lie nearest the Sun, and least at the opposite extremities, being most distant from it; in other words, they move quickest when near and slowest is aphelion. Although the matter is somewhat technical, I shall here, in order to make these general statements comprehensible, the laws regulating the motions of the planets which bear the name of Kepler. They may be stated as follows : 1. The planets move in ellipses, having the Sun in one focus. Fig. 70. The Indications of the Axes of the Planets to the Equator. Original Surveying Instruments THE PLANETS GENERALLY. 2. The radius-vector of each planet describes equal areas in equal times. 3. The squares of the periodic times of the planets are proportional to the cubes of their mean distances. These laws hold good for all the planets, and also for all their satellites, and for all the comets which have been observed. A few words may be added to make these laws a little more clear to the non-mathematical reader. Everybody understands what is meant by a circle, i.e., that from the centre every part of the circumference is equidistant, but in the case of an ellipse, there is no such centre inside of which it is equidistant from the cir- cumference, and, in order to draw such a figure, one must make use of two points inside. Each of these points is called a "focus." A radius-vector is an imaginary line drawn from the Sun to a point on the circumference of the ellipse which constitutes the planet's orbit. The statement that the radius-vector of each planet describes equal areas in equal times will be best grasped by an inspection of Fig. 71, where the shaded portions represent equal areas, whilst the distances along the circum- ference, though very unequal in extent, are yet traversed by the Diagram illustrating Kepler's Second Law. Fig. 71.--Diagram illustrating Kepler's Second Law. 60 KEPLER'S LAWS. planet in equal periods of time. Such is the case because every planet moves when nearest the Sun than it does when farthest off from the Sun. Kepler's Third Law involves a curious point: if the dis- tance of the Earth from the Sun be taken as unity ('1'), and its period of revolution as 365 days, then the distances of the planets be divided by the cubes of their mean distances from the Sun, the result in quotients will be the same substantially for all the planets, the slight discrepancies in the quotients being due to errors in the observations on which the calculations are based. This law applies to all the satellites, so that an identical quantity will be obtained for each group of satellites, though comparing one group with another, the quotients will vary inter se. The foregoing statement, calculated for the planets, is exhibited in the following table ---
Planet. Distance from Sun Period in days Quotient
Mercury 0.3870 87.969 1.31421
Venus 0.7230 224.714 1.32413
Earth 1.0000 365.255 1.33408
Mars 1.5299 686.979 1.34310
Ceres (as typical Minor Planet) 27.960 1697.89 1.35210
Jupiter 5.2050 4332.84 1.36294
Saturn 9.5858 10470.29 1.37373
Uranus 19.2168 30875.69 1.38468
Neptune 30.9057 60142.72 1.39413
To draw an ellipse, the following points must be borne in mind. The eccentricity of an ellipse is the ratio of the distance between the centre and one focus to the length of the semi-axis-major. It is usually given as a decimal fraction, 62 THE PLANETS GENERALLY. the semi-axis major being taken as unity, or 1°. Thus, an eccentricity giving as 0.2 means that the distance between the centre and either focus is 5th of the semi-axis-major. This is sometimes symbolised by the Greek letter $\phi$ and with an angular measurement named. In that case the eccentricity is obtained by finding from the tables what is the natural sine of the angle $\phi$. In order to draw an ellipse of a prescribed eccentricity first of all draw a line AB representing the axis of the ellipse, then take as the major of the intended ellipse; bisect it and mark the point of bisection; then from the centre set off in each direction along the line, according to the selected scale, distances equal to the natural sines of the angles which represent the required ellipse. Fix pins at these points and at one of the extremities of the axis, and then proceed as follows. Tie a loop of thread round one pin, stretch it tautly over the pin which is at the extremity of the axis-minor; stretch the thread tightly with the point of a pencil and move the pencil round under the guidance of the thread kept tautly drawn. Perhaps an actual example in figures will make the modulus apparent of this more clear. Say you want to draw an ellipse of 30° eccentricity. Draw a line AB representing the axis (see white paper or card-board); bisect it; set off on each side of the point of bisection distances of 33 lines ($i.e.$ 7½ half-lines), these points being A' and B'. Then proceed with the aid of the thread as above. Of course any units may be employed in devising a scale, but perhaps inches, as in the above example, will generally be found most convenient when it is desired to simulate the form of a planetary or cometary orbit. Sir John Herschel put forth, many years ago, a fancy statement for the purpose of enabling a reader to obtain a rough general idea of the dimensions etc. of our supposed neighbouring planets. The statement needs some revision and correction. A diagram showing how to draw an ellipse with a given eccentricity. THE DISTANCES OF THE PLANETS. 63 to meet present circumstances--treatment which I have applied to it; and I now present it in the following form: Mercury will be represented by a globe 2 feet in diameter by way of representing the Sun ; Mercury will then be represented by a mustard-seed at a distance of 32 feet; Venus by a pea at a distance of 142 feet; the Earth also by a distance of 215 feet; Mars by a small pepper-corn at a distance of 300 feet; Minor Planets by grains of sand, of different sizes varying from 500 to 600 feet, from a moderate- sized orange 4th of a mile to the central point will Jupiter; a small orange 1ths of a mile, Saturn; a full-sized cherry 1ths of a mile, Uranus; a small apple 1th of a mile, Neptune; and Pluto. The last two are unknown yet known, though astronomers suspect there exists another planet still farther off and hope one day to find it. Extending this scheme, the aphelion distance of Encke's Comet would be 880 feet; the aphelion distance of Donati's Comet 6 miles, and the nearest fixed star 7200 miles. Fig. 72.—Conjunction of Venus and Saturn, Dec. 19, 1845.
64 THE PLANETS GENERALLY. An idea of the absolute movements day by day of the planets in their orbits would be obtained by imagining Mercury to move every day 3 feet; Venus 2 feet; the Earth 12 feet; Mars 1½ feet; Jupiter 10½ inches; Saturn 7½ inches; Uranus 5 inches; Neptune 4 inches. These figures serve also to illustrate the fact previously mentioned that the earth's velocity decreases as its distance from the Sun increases : and by a vast increase of the imagination we might suppose a planet in the Universe where a planet would always move round the Sun at all, in other words, where all motions would cease so far as a solar system was concerned. Fig. 73—Conjunction of Mars and the Moon. Sept. 28, 1909. A matter of some interest as a spectacle, is the occasional conjunction of two or three planets in the same part of the heavens. It is exceedingly rare to get more than two planets together in the same field of a telescope, but a combination of two only is not at all uncommon. Besides those which are here illustrated, some more recent instances may be mentioned: A diagram showing a conjunction between Mars and the Moon. CONJUNCTIONS OF THE PLANETS. 65 In September 1838 Mercury and Venus were together in the same field of the telescope for some hours. According to Naismith, the conjunction of the two planets was very marked. Venus looked like clean silver, whilst Mer- cury had more the appearance of lead or zinc. This last statement is not true, because Mercury is generally credited with being of a rosy hue. On August 9, 1838, Venus, Saturn, and the bright star Geminius were in the same field. On May 17, 1840, Venus and Mars were very close to one another, Venus being of $c^{\prime}$ to the south. That same month of May 1905 yielded two other con- junctions between telescopes armed with low-power eye- pieces having large fields. On May 11 Venus and Jupiter were close together, Venus being $c^{\prime\prime}$ to the N., Mars being $c^{\prime\prime}$ to the S., and Jupiter being $c^{\prime\prime}$ to the E. On May 16, 1840, and Jupiter and Saturn were together, both being $c^{\prime\prime}$ N. Such a succession of planetary conjunctions, conspicuous planets being involved, is unique. On October 20, 1840 Mars and Saturn were within $2^{\circ}$ of each other, and therefore in the same field. McEwen, at Glasgow, remarked that: "Saturn presented a bright chrome colour in contrast to the bright ochre tint of Mars. It must, however, be admitted at a distance that the difference in their colours is not com- pared with Saturn with its rings, although to the naked eye Mars appeared much the brighter of the two planets." An observer in America, Conroy, at Los Angeles, wrote much to the same effect: "The difference in the colours of the two planets was not so great as I supposed it would be. Mars glowed with his usual strong, ruddy hue. To the naked eye, and still more in a field-glass, Saturn was decidedly yellow, with a greenish tinge." 60 THE PLANETS GENERALLY. The 18th century produced a planetary conjunction which, if correctly ordered, must have been singularly striking, for it is said that Venus and Mercury, in their perihelion, were all seen together in the same field of the telescope. Whilst we nowadays clearly understand that the Sun is the centre of our system, and that the planets revolve round it, it is quite a thing of modern times, being hardly more than three centuries old. Our system has been called the Copernican System, from the Polish astronomer, Copernicus, who gave it shape. But it was not until the time of Kepler (1571-1630), indeed for a century or more later, there were rival systems in the field. They may be named in something like the order of the following: the Ptolemaic System, the Egyptian System, and the Tychonic System. The following pages will describe these in detail. The question of a natural one : Are there more planets circulating round the Sun than those already spoken of? It is probably true to say that there are, and the question of a planet within the orbit of Mercury, and also of one beyond the orbit of Saturn, has been discussed by many astronomers, though without any very certain results. The romance of an intra-Mercurial planet caused great excitement at the heart of odd years ago, and many were fasinated with this theory. In 1846, however, Leverrier's idea of a Trans-Neptunian planet has not yet reached the stage of romance, much less that of fascination. CHAPTER VI. THE MOST INTERESTING AND FAMILIAR PLANETS. A classification of the planets—Mercury—Difficult to observe.—Spots—Phases—Schiaparelli's observations—Axial rotation—Satellites—Mercury resembles those of Mars—are—Physical Features—Possible moon- tains—Tidal forces—Mercury is the nearest neighbour—Cele- brated by its markings—Mariner—the Earth's nearest neighbour—Cele- brated by its markings—The Sun's nearest neighbour—is accessible for observation.—Its apparent movements.—Physical appearance of the Sun.—Sunspots—Sun-spots are permanent.—Its colour.—Satellites.—Statistics.—Jupiter—The largest planet in the Solar System.—Satellites.—Jovian spots and Sun-spots.—Satellites.—Largest ones easily found and observed.—General description of them.—Their movements from time to time.—Some details respecting them.—The bands of Jupiter are tests for telescopes.—Statistics. The classification of the planets in a previous chapter into "inferior" and "superior," though desirable from a scien- tific point of view, has been adopted only by the popular observer of astronomical phenomena, who is con- cerned more particularly with what he is able to see. According to this classification, there is one group of clas- sification, which cuts across the previous one, because of its being framed upon quite a different basis. Whilst one group responds readily to the general title of the "Interesting and Familiar Planets," it would be somewhat unphilosophical to 68 THE MOST INTERESTING AND FAMILIAR PLANETS. gibbet the residue as the "Uninteresting Planets," for the statement would not be true of some of them, and I can only give a few of the more interesting objects which do not attract the notice of the generality of readers." Under the title of "Interesting" and Familiar Planets I shall deal with Mercury, Venus, Mars, Jupiter, and Saturn, all of them being bodies of general brightness to attract the notice of almost everybody from time to time ; but Venus, Mars, and Jupiter, under all circum-stances, will always be regarded as the most interesting planets. The orbit of the Earth, can never be very far from the Sun. Venus, however, on occasions, shines with such splendour that twi- light is lost in its brilliancy. Jupiter is a planet of great size; however, being so much nearer the Sun than Venus, is more difficult to find and follow, because it is never out of bright twilight. The other planets belonging to this chapter—Mars, Jupiter, Saturn—are all very large bodies, and they are all, and as they wander all over the heavens, one or other of them is almost always in view at some hour of a given night. Inasmuch as all these five planets have special features of their own, we will well be to give them sections of this chapter to themselves. MERCURY. Mercury does not receive much attention, owing to the dif-fi-culties of seeing it, as already stated. Its greatest possible elongation from the Sun cannot exceed 27° 45' (and it being in general much less), the difficulty is obvious. The greatest possible elongation on the E. side happens at the "evening star"; whilst the greatest possible elongation on the W. side happens in September, when Mercury is a "morning star." The chances of seeing it are best for us England when an elongation coincides with a northerly position of the planet MERCURY. 69 in declination, even though the elongation is less than it might be at other times. It may often be seen with the naked eye, shining with pink or rosy light. It was so seen by many observers in April 1805. The observations of Schröter at Lilienthal, and of Sir W. Herschel, led them to think they had obtained decisive evidence of high mountains on the planet's surface, and that on the contrary, the markings in its southern hemisphere manifested its presence by the planet's southern horn having a triangular (or blunted) appearance near Inferior Conjunction, which must be due to a mountain obstructing the light of the Sun. This view is far as the point to which the cusp theoretically ex- tended. In 1882, in 1883, I saw some dark irregularities on the face of the planet; also a brilliant spot and a large white area. The southern horn was then completely truncated. He states that his results led him to infer that the markings upon Mercury are far more decided and more easily discernible than those of Venus, and that their surfaces are much smoother than that of Mars. A French observer, Guion, in 1884, remarked on September 17 that both the horns of Mercury (then almost a semicircle) were truncated; but that only the southern horn Fig. 4. Mercury, Sept. 17, 1885. (Guion.) 70 THE MOST INTERESTING AND FAMILIAR PLANETS. was so five days later. He mentions no signs of shading or spots. I have already stated in a previous chapter that Mercury is subject to phases, and will repeat here the bare fact only by way of illustration. It has been shown that the apparent diameter of the sun has been found that the illuminated portion is less than it should be, according to calculation. This statement rests upon the testimony of Messrs. Lalande and Delisle, but their unexplained explanation is the more difficult because of their un-sufficient evidence that Mercury possesses an atmosphere. There is some ground for the opinion that it is more easy to notice the phases of Mercury than those of Venus, owing to its proximity with Venus. More than one observer besides Denning, quoted above, has gone so far as to suggest that, if viewed under favourable circumstances, the phases of Mercury would surpass more nearly the visibility of Mars than any other planet. The astronomer who in recent times has made the most systematic study of Mercury is Schiaparelli, some of whose observations are given in his "Catalogue of the Planets." He has the best chances of studying the planet's surface to be when the Sun is above the horizon, and that the resulting inconvenience is less distinct than when he can view down towards the horizon when the sun is absent. He thought, indeed, that some of the markings which he noticed were permanent; hence the supposed axial rotation was considered to be slow. The conclusion on this rationalisation of Schiaparelli's conclusions is that Mercury's axial rotation takes place, not in the 24 hours, or thereabouts, generally accepted for our own planet, being the period occupied by the planet in going round the Sun. This conclusion is mentioned because of Schiaparelli's experience and standing as an observer, but it is impossible to accept it without further proof of our knowledge, though some other observers, including Lockyer, in 1864, have seemed inclined to agree with Schiaparelli. MERCURY. 71 By means of a dark spot seen in April 1904, McHarz fixed the period of rotation at 24.8 m., which accords with all previous values except Schiaparelli's. Mercury revolves round the Sun almost exactly 88 days at an average distance of 35,000,000 miles, which may vary between the limits of 43,347,000 miles and 28,370,000 miles. These great extremes in the distance of Mercury from the Sun are due to the fact that the planet does not exactly follow the planets' orbit, which is greater than that of any of the older planets, though exceeded by many of the Minor Planets dis- covered in modern times. The apparent diameter of Mercury varies from about 16 to 25 minutes of arc in Inferior Conjunction. The real diameter may be taken as about 3,000 miles, or perhaps a little less. It may be useful to readers to suggest to them a convenient method for finding either Mercury on Venus in daylight by means of a telescope unprovided with an equatorial mounting or circles. For the successful use of the method certain conditions must be fulfilled. The observer must have a telescope and the planets are required. The telescope must be perfectly steady on a substantial stand, and anchored in such a way so that it cannot be after being once placed in its semicircular position, be turned around; and it must be provided with an eye-piece of low power having the largest possible field. The planet to be sought must have a declination sufficiently high to bring it into sight or out from that of the Sun, and the planet's right ascension must be greater than that of the Sun. If the difference of declination much exceeds 3° the chances of picking up the planet will be much diminished. The above conditions being fulfilled, the method consists in using the Sun to find the position in the sky which corresponds with that of the planet. By observing this point during periods to what is believed to be about the planet's declination, the observer has only to wait until, by the rotation of the Earth, 72 THE MOST INTERESTING AND FAMILIAR PLANETS. the planet is brought into the field of the telescope. Two further preliminaries must be observed : the telescope must be carefully focussed either on a Sun-spot or by means of the Sun's limb. A dark glass must be used in doing this, and while this has been done a pale neutral should be used whilst the planet is being viewed. Accurate focusing of the telescope is very important ; other- wise the planet may escape the eye which is looking for it, because of its small size. The telescope must be carefully focused, having been assured, the Sun must be carefully brought into the centre of the field, and the line along which it travels into the field must be carefully noted. This is done most easily if the eye-piece is placed at right angles to the axis of the telescope, with two wires crossing each other. The Sun having been brought to the centre of the field, the telescope must then be turned (for downwards) at right angles to the apparent line of the Sun's movement by the amount of the difference (estimated from the centre of the Sun) between that right angle and that of its right ascension, the centre of the field being taken in both cases as the point aimed at. No circles being available, the observer should remember that when he brings the Sun's disc being approximately 3°, the telescope must be moved vertically by as many half- degrees as equal the difference between the declinations of the Sun and that of his right ascension. For example, if the difference is 21°, the telescope must be moved by the amount of 5 degrees of the Sun. The observer has now nothing more to do but to wait with his eye at the telescope until he sees that part of the disc which corresponds to the amount of difference between the R.A. of the Sun and that of the planet.¹ For further details and examples of this method, which was put forward by Mr. J. R. Ryle, see The Journal of the British Astronomical Association, vol. vi., p. 60, December 1904. 72 Figs. 73-77 PLATE XXIV. A series of three images showing the phases of Mercury during its transit across the Sun on November 7, 1881. (1) Nov. 7, 2:45 a.m. Mercury in 1881 [H. F. Dreyer]. (2) Nov. 7, 4:00 a.m. Mercury in 1881 [H. F. Dreyer]. (3) Nov. 7, 6:00 a.m. Mercury in 1881 [H. F. Dreyer]. 74 Fig. 78 PLATE XXV. A diagram showing the various phases of Venus. 1. A small, round, white circle representing Venus. 2. A larger, crescent-shaped, dark grey circle representing Venus during its first quarter phase. 3. A smaller, crescent-shaped, dark grey circle representing Venus during its third quarter phase. 4. A large, circular, dark grey circle representing Venus during its full phase. The Various Phases of Venus. [2] VENUS. 73 VENUS. What has been said already with respect to Mercury will have paved the way for the mention of things which will now have to be said about Venus, but, as regards one matter--its brilliancy on occasions--it is worth noting out in advance of all the planets. Such is the case with Venus, however, we look at it in the evening or the morning, fulfilling its function in popular parlance, of the "evening star" or "morning star." But on certain occasions, at rare intervals, this planet is at or near its greatest N. Lat- titude, and for 5 weeks from Inferior Conjunction, it shines with surpassing splendour, equal to, or even greater than, Venus near its Inferior conjunction. (Schiller.) Fig. 79.--Venus near its Inferior conjunction. Venus, Dec. 23, 1885. (Lakow.) Fig. 80.--Venus, Dec. 23, 1885. 74 THE MOST INTERESTING AND FAMILIAR PLANETS. that of Sirius (a Canis Majoris). This only happens about once in 8 years, and occurred last in 1910, and will recur in about 1926. The appearance of the planet Venus also casts a shadow. Such was the case on January 12, 1902, as recorded by Giacomo at Nice. The appearance of the moon seems to follow quite naturally that the planet is often readily visible in the daytime, especially if, by means of graduated circles, the seeker knows exactly where to look for it. It is the opinion of those who have made a special study of this subject, that when the moon is high, it is easier to detect its physical features by daylight, or in quite early twilight, rather than when it has a dark sky behind it. There is no doubt that the moon is more easily seen when the truncature of one or both horns when the planet shows as a crescent; and these facts indicate beyond doubt not only that the visible surface is not even, but that mountains exist on it. It is probable that there are also some large lakes, some mountains, less precise words, such as markings, or shadings, or spots being used. As regards the observer, M. Lacerda has stated that the southern horn is always longer than the northern one ; that is to say, that the northern one is often more blunt than the southern one. The same observer remarked that the most favourable time for observing Venus is between half an hour before and one hour after sunset ; and that the corresponding times at sunset, when the planet was in the W., seemed to be between 3 and 5 hours after sunset. As regards the physical appearance of the surface of Venus the difficulties are very much the same as those which are encountered with Mercury. The surface appears to be very uneven ; that is to say, in addition to the blunted horns already mentioned, spots are visible from time to time. It is from these facts that the conclusion has been drawn that, as in the case of Mercury, mountains probably exist ; but See p. vii, note. VENUS. 75 there is a conflict of opinion as to whether these mountains have an objective existence on the body of the planet, or whether the shading which they produce over the mountain-tops, are merely shadings in an atmosphere which simulate mountains. It has been shown that Venus has an atmosphere of considerable density seems well established, especially by the appearance presented by the planet when under observation during transit across the Sun. A further proof of the existence of an atmo- sphere was furnished by the observations made at the time of occultation of the star Geminorum by the planet. The star's brightness diminished rapidly during 2 or 3 seconds before its disappearance, and then rose again after emergence. It was thought by the French observers who noted these results that a variation of light during 2 seconds would indicate a layer of atmosphere about 68 miles in height. There is such a considerable difference between all the various figures arrived at as regard Venus's atmosphere that its reality and considerable extent are open to no doubt. Per- haps it may be added here that this is one of those cases where When Venus is near its Inferior Conjunction there may sometimes be noticed an appearance not unlike the Lumière effect, but which is frequently visible when the Moon exhibits a narrow crescent, as described in the previous chapter. (Ann. p. 36) Though this phenomenon has been seen and recorded by many observers, yet for a long period of time, the most careful and complete observations are those which were made by Zenger at Prague in 183x. Without quoting the details generally given by him, I will only mention some of them, namely, all the phenomena which are presented by Venus when its disc is partly illuminated and partly unilluminated find a complete counterpart in what we see when scrutinising the Moon; and that the varying tinges, sometimes simply dark, are analogous to what we often see in looking at a "young" Moon, or (the A diagram showing the phases of Venus. 76 THE MOST INTERESTING AND FAMILIAR PLANETS. Moon eclipsed. In other words, that, as we know the variations in the Moon's appearance which we see from time to time under different circumstances, and as we know also how these vary with the Earth's atmosphere, so the different appearances presented by Venus depend upon the varying conditions of the atmos- phere of Venus. We have seen that, in the case of Mercury, this theoretical breadth of vision does not always accord with the theoretical breadth which ought to be shown at that particular stage. The same discrepancy occurs in the case of Venus. There once raged a long controversy, spread over many years during the 18th century, as to whether Venus had a satellite or not. It was supposed that she had one, and that it was stationary, and proceeded from many observers; but there is now no question but that they deceived themselves, and in their small telescopes mistook stars for companions to the planet, for it is only since the invention of the telescope that such things have been recognised long ago in some of the many great telescopes which were brought into use in the second half of the 19th century. The planet Venus has always occupied a prominent place in the literature of poets and historians during more than two thousand years. It would occupy too much space to offer any question about its history. It is associated with a word (the word) which is associated with the planet and which deserves mention, especially because, as we go along, we shall find that the history of this planet is closely connected with that of olden times, say three centuries ago, before the days of Copy- right and Patent Laws and "Merchandise Marks Acts," when a man discovered something that he thought was new and worth attention. Thus it was announced in his obscure phrase- ology, which secured him the priority of credit without disclosing his discovery in detail. Thus it was that Galileo, who dis- covered the phases of Venus, is said to have announced his discovery in the following Latin logographie, or anagram: 76 Figs. 81-86 PLATE XXVI. March 22, 6 h. March 26, 7 h. March 28, 63 h. March 20, 61 h. March 31, 64 h. April 5, 64 h. Venus, 1881 (W. F. Denning). **PLATE XXVII** Figs. 87-92 May 14, 83 in spec. (W. F. Galle). April 14, 122 in spec. (P. B. Makemson). April 19, 91 in spec. (T. E. R. Phillips). April 23, 21 in spec. (P. B. Makemson). May 21, 5 in O.G. (R. Kellio). April 8, 64 in spec. (H. Conder). Mars, 1903. [77] VENUS. 77 "Hex immatura me, jam frustra, leguntur-oy" ("These things are ripe at one time (read) in vain [by others] are read by another time") "The me" being "the me" of Venus. This Latin sentence, when transposed, becomes: "Cynthia figuras matulum Mater Amorum" ("The Mother of the Loves [Venus]") "et ego" ("and I"). The letters "oy" are, it will be observed, redundant, so far that they cannot be made use of in the transposition. Therefore we may believe that the special brightness of Venus at its best is due to the reflection of a large portion of things which enables it to reflect a larger proportion of the Sun's rays falling upon it than is the case with Mercury. It is also probable that Venus can be seen and ascertained up till how long before, and how soon after, Inferior Conjunction he can see Venus in a telescope. The interval ought only to be one day or two days. Venus travels round the Sun in 224 days at a mean' distance of 67,000,000 miles. The orbit is nearly that of a circle, its eccentricity being the smallest of all the orbits of the planets. It is therefore called an "ellipse," but it is nearly circular. The apparent diameter of Venus varies between 9° in Superior Conjunction and 65° in Inferior Conjunction. At this latter period it appears diametrically opposite to the Sun. This distance is about 7500 miles; that is to say, Venus is nearly, but not quite, so large as the Earth. The period of its axial rotation is disputed, but it probably amounts to about 234 hours. MARS. We will now proceed to the important planet Mars, passing over the Earth for the reason already given: that, though the Earth is a planet, and a very important one too, we cannot, because we are on it, study its appearance in the way in which, with the assistance of telescopes, we study the appearance of other planets. 78 THE MOST INTERESTING AND FAMILIAR PLANETS. Mars and Jupiter, which will occupy our attention in the next section, are the planets which most often attract our notice in the heavens. They are very bright, and they are always visible at some time or other between sunset and sunrise. Moreover, Mars, by reason of its normal fiery colour, can never be mistaken, or at any rate should never be mis- taken, for the Sun. The Sun is always seen in the same place, Mars exhibits, on occasions, a slight phase, but it is not very noticeable. When the planet is in Opposition—that is to say, when it is opposite the Sun—it is seen in a circular disc; but at other times it is gibbous, the maximum defalcation of light occurring when the planet is in Quadra- ture, or 6 hours away from the Sun, either E. or W. At these times we see the Moon 3 days on either side of the epoch of Full Moon. By reason of its proximity to the Earth, it comes into Opposition with us every 2 years and 5 months; it may be met every 780 days, this being what is called its "syndic period." When in Perihelion (that is, nearest to the Sun) and in Aphelion (that is, nearest to the Earth) it times coincide with that of Jupiter, Mars rivals Jupiter in brilliancy. This happened last in the summer of 1909, and will not occur again until 1924. But the fact that we have had two such brilliant conjunctions within a few years gives us great facilities for studying it, and should be an encouragement to tracing its movements in the heavens amongst those of the other Superior Planets. In the case of the other Superior Planets because they take so many more years in making their circuits round the Sun, and move so much slower among the stars. It will be interesting, there- fore, to see how long it will take them to pass through Earth see them. Starting when Mars has just passed through Conjunction, it emerges from the Sun's rays, rising some minutes before the Sun, and having a direct, that is, easterly motion; but as this motion is only half that of the Earth in the Figs. 93-98 PLATE XXVIII. May 13, 61 in spec. (F. E. R. Phillips). April 30, 12 in spec. (P. B. Molesewski). March 31, 81 in spec. (F. M. Antoniadi). March 35, 61 in spec. (E. A. Z. Atkinson). March 35, 61 in spec. (P. J. Hailly). May 7, 61 in spec. (F. E. R. Phillips). 5903 Fig. 99-100 PLATE XXIX. Sept. 20, 1905. Nov. 3, 1905. Mars (Antonini), 79 MARS. 79 same direction, Mars appears to recede from the Sun in a westerly direction, notwithstanding that its true motion towards the Sun is always eastward. It reaches the Sun nearly a year, and ceases when it has attained an angular distance from the Sun, measured along the Ecliptic, of about 13°. Then for a few days it does not seem to move at all. It then begins again to move westward among the stars, and so continues until it reaches a point 180° from the Sun, or, in other words, it is in Opposition or on the meridian of the Sun. After this time its retrograde motion amongst the stars attains its greatest rapidity, but it soon slackens and becomes slower and slower until it has arrived at a point 13° from the Sun. Then it begins again to move eastward till once again the planet is lost in the Sun's rays, soon after which it reaches Conjunction, and another two-year period of changes ensues. In this way, during each period of 280 days there will be changes in the details ; the retrogradation does not always commence or finish at 13°, for it may begin as soon as 10° or as late as 20° before it has reached 13°. The arc described varying between 10° and 19° is called the duration of the retrograde motion in the former case is 60 days, and in the latter 80 days. The period in which these changes take place is called the synodic period. Two successive Conjunctions or two successive Oppositions, constitutes the synodic period of 280 days already mentioned. The motions of Mars have been observed with our telescopes may be regarded as not subject to much change except in one particular. I say this advisedly, because although during the past 30 years there has been a great controversy respect- ing whether or not the supposed change in its orbit there has been a great disquisition to indulge in extraneous language, there is abundant evidence to show that there are certain defined marks which are unchanged and are probably unchangeable. 80 THE MOST INTERESTING AND FAMILIAR PLANETS. I will deal with and dispose first of all, of the appearances which are most remarkable and characteristic of the Moon, being one particular exception to the rule of universal invisibility. This statement refers to the spaces around the poles, which are commonly reputed to be signs of the existence of snow. I think that this is a mistake, and that these appearances have been observed to diminish when brought under the influence of the Sun at the commencement of Mars's summer, and to increase again on its return into winter. The illustrations accompanying are sufficiently self-descriptive. Some anomalies have been noticed from time to time in regard to these polar patches, not sufficiently great, however, to be considered as anything more than accidental. They are very strange. For instance, whilst both Mädler and Secchi found the north patch to be concentric with the North Pole of the planet, Sir W. Herschel, in his catalogue of 1784, stated that the South Pole. Sir W. Herschel, as far back as 1784, noticed that the patches were not exactly opposite to one another. Spots on Mars are frequently seen, and have enabled astronomers to determine the period of the planet's axial rotation, which may certainly be set down at 24 hours 37 minutes. The following (the obviously wrong word) of the surface of Mars has been attentively studied during the three centuries which have elapsed since the invention of the telescope, and drawings of every kind, by astronomers of every sex and nation, have been made. The result is most remarkable. No wonder the whole globe has been mapped out into areas, hypothetically regarded as land and water, and even mountains and valleys have been described and given. The original series of names was restricted in number, and included the names of some twenty leading observers of note in the astronomical world. Without saying that these names have been formally discussed, yet a new series of names, Latin in form and in a certain sense mythic, have Fig. 389a. PLATE XXXIX A color photograph of Mars, showing its surface with a prominent dark spot in the center. The planet's surface features include various shades of red, brown, and white. Signature at bottom left corner MARS. October 21, 1909. (8. BoZem) [API_EMPTY_RESPONSE] MARS. 8$ been brought into use and seem to be meeting with acceptance from astronomers. After the polar patches spoken of already the one most obvious feature which most generally attracts notice when that particular hemisphere of Mars where it is situated happens to be under observation, is the "V" mark, from resemblance to that letter; but which much more readily brings to mind the continent of South America. This "V" mark is seen at right angles at some northern tip at right angles to the general trend of that con- tinent. The shape of a leg of mutton has also been suggested. The ruddy colour of Mars has been notorious from the earliest times. It was first noticed by the ancients, and handed down, and Sir John Herschel ascribed it to "an ochre tinge in the general soil like what the red-sandstone districts on the Earth may possibly offer to the inhabitants of Mars," only this idea is not so far-fetched as might at first be thought. There are parishes in Gloucestershire, one of them being Redheath, which have been named after Mars, which would bring home Herschel's idea. There might easily be imparted to the Earth, when viewed from Mars, a very distinct reddish colour opposite to that of the Earth, and this would make all geologically resembling the soil of the parish of Red Marley. Another long-standing idea with respect to the surface of Mars is that it is vividly divided, as the Earth is, into land and water. The green areas being land and the alpine or equally green areas being water. The great controversy of the present day respecting Mars is the question whether it has life or not. Some naturalists said it exist all over it, and to show themselves in the form of numerous dark lines, very straight, and so well defined as to indicate for them an artificial origin. The observers who first put forth this alleged fact and its explanation had for a few suppositions, or men who have been considered such because 6 82 THE MOST INTERESTING AND FAMILIAR PLANETS. they thought they had seen markings on the planet which might be regarded as straight lines intersecting one another at various angles, but that these lines were merely due to the vast majority of observers, using telescopes of every size and kind, have never suggested the existence of any such precise markings, or been able to find them when invited to look for them. Professor W. H. Pickering, taking an intermediate view, has reviewed the controversy respecting the markings on Mars in the following terms:— "It has lately been shown by Messrs. Lane, Maundur, and Evans that the canals in the inner Martian canals are probably non-existent, their appearance being due to certain singular optical illusions. Most of the broader canals, however, in the dark regions of Mars appear to be real, and it is probable that they are certainly true of some of those in the light regions, such as Arabia Terra and Tharsis. The canals may be supposed to be the system of lakes, or oases, as they are sometimes called, which were first discovered in large numbers at Argyre Planitia." "There is a curious tendency of the human eye to see such dark portions of the surface of Mars as being traversed by means of diagrams that these lines sometimes appear when the diagram is at such a distance that the dark dots are themselves invisible. This effect is produced by two different causes: it appears, joining different portions of the dark regions. We may call this phenomenon spurious canals. There are two classes—those that are genuine and those that are not." This phenomenon of spurious canals is certainly very singular and interesting; but we must not allow our imagi- nition to lead us into the error of affirming that, because many people have seen these canals, they must necessarily exist. They may be imaginary. It seems indeed a great pity that so much time and energy should have been expended in many observations upon this subject, while comparatively so little time spent on the darker regions, where changes are constantly taking place, and where we should naturally expect the more interesting developments to occur." 9/22 Fig. 101 PLATE XXX. Chart of Mars on Mercator's Projection (drawn by E. M. Intenaday). A chart of Mars on Mercator's projection, showing various features and labels. 82 Figs. 102-107 PLATE XXXI. Jupiter. A series of four black and white photographs showing Jupiter's surface with prominent dark spots and light bands. [83] MARS. 83 At one time it was urged that, not only was Mars crossed and recrossed by sharply defined dark lines, but that many of these fine lines were so regular and parallel as to be almost certainly applicable to them. Weighing the *pro* and *con* of the contro- versy on the principles of the law of evidence as applied by lawyers, I cannot consider that the arguments put forth in support of this view have been sufficiently strong to establish it, and think that the only thing which is established is, that there are numerous markings on Mars which take various shapes and forms, and which are very often seen at night, and that very often they are not clearly visible. Firstly, that their visibility depends in no small degree on the personality of the observer and on atmospheric and other circumstances. The most remarkable of these markings which has yet to be mentioned, namely, its satellites. Though these cannot be said to concern the general reader because of their diminu- tive size, they are interesting enough to mention with them. They were only discovered as recently as the year 1877, when an American observer, A. Hall, conceived the idea of turning to account the favourable Opportunity of that year to observe Mars. He obtained a powerful telescope of the Washington Observatory, carrying an object- glass 26 in. in diameter. His efforts were soon rewarded by the discovery of two satellites which he named Phobos and Deimos, the names of the steeds said by Homer to have drawn the chariot of Mars. What is stated about Phobos is not more than a star-like magnitude 11, whilst Deimos is faint at a star of Magni- tude 13, it will be realised at once that only telescopes of very large size can observe them. Historically it is interesting to note that this discovery was made by a man who had been spoken of as having discovered that Mars had two satellites, whilst Voltaire, in his "Romance of Micromegas," ascribes to some of his characters also the discovery of two Martian satellites "which had escaped the scrutiny of our astronomers." 84 THE MOST INTERESTING AND FAMILIAR PLANETS. It is to be presumed that Voltaire was only a copyist of Dean Swift. Many travels round the Sun in 686 days, at a mean distance of 14,000,000 miles. The eccentricity of the orbit, though a good deal less than that of the orbit of Venus, is nevertheless considerable, so that the planet may be from 13,500,000 to 14,500,000 miles distant at its nearest approach, and at its greatest distance from the Earth, which may occur when it is great at 14,000,000 miles or as little as 12,500,000 miles. The planet's apparent diameter varies between 4 in Conjunction and 3½ in Opposition. Owing to the inclination of the axis of rotation with respect to the ecliptic, seen from the Earth, it will also differ greatly at different times. The real diameter may be regarded as almost exactly 5000 miles. JUPITER On the whole, Jupiter may be said to be the planet most easily brought within the reach of everybody, and for this reason ; it is generally visible for many months in every year ; it is more or less conspicuous owing to its normal brightness, and its rapid motion across the sky. Its satellites and principal satellites are within the reach of quite small telescopes. Indeed, instances are on record of the satellites, when sufficiently near to the Earth for their light to be visible by daylight, having under favourable circumstances of atmospheric transparency been seen by the naked eye. Jupiter is the largest of all the planets, having a diameter nearly double that of Saturn. In consequence of its long axis in the short time of 10 hours or thereabouts, it follows that, by the laws of rotary motion, the compression of the polar regions is greater than that of the equatorial regions. It is one of the best authorities, to about 4th of the equatorial diameter. The belts have long been known as a notable feature of the planet. There is a certain amount of permanency about them, yet it cannot be said that they are permanent. To look upon them, they are darkly streaks of different thicknesses, which PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 PL-03 Pearl Street [API_EMPTY_RESPONSE] JUPITER. 85 breadsths vary from time to time. Sometimes they chiefly appear as two or three broad belts, at another time the observed number of belts may be much narrower than those he may have seen on some previous occasion. They are all parallel to the planet's Equator, though commonly absent actually under the Equator. On very rare occasions they may be found crossing the Equator in the general trend of the belts. The latest recorded instance of this was in April 1910, Bolton being the observer. It may be worth remarking that when we look at anything in the nature of a solid body, but only at a cloudy envelope, which may or (more likely) may not enclose a solid body. It has been suggested that the change is visible on Jupiter due to the manifestation of energy in the form of heat on the planet. The question as to their colour seems obscure because, though they are often described as a single band of blue, it can be traced, whilst in 1873 a great red spot burst forth, which remained for many years a striking and permanent feature. The latter phenomenon is one of those things which are in mystery about it which is still unresolved. It retained its shape and colour for about four years, up till the autumn of 1882, when it began gradually to fade; and during the ensuing years it became more and more irregular in shape and form. In the years between 1884 and 1900 it underwent various changes, never recovering its original bright colour. In 1906, however, it reappeared, the tinge of colour was no more than grey, though sometimes it was red. This was so strange as to be suspected. In 1909 the spot was all but invisible, though although its outline could be detected; but it more than ever presented the appearance of a dark ring round a dark base or hollow. In 1910 it again became visible, though only for a few weeks, and now one can hardly say more than that its place can be discovered. The illustrations annexed will indicate the fact that such 86 THE MOST INTERESTING AND FAMILIAR PLANETS. the red spot's visibility, dating from 1787, its original outline was oval, and that, notwithstanding the loss of colour, which marked it during those years, yet at times it seems to have closed up and lost its distinctness. The question has been mooted whether the oval spot of 1878, with its strongly defined colour, could be identical with an elliptical ring which was observed on Jupiter in 1769 by D'Alembert, and again in 1780, 1782, but which did not possess any definite colour. That elliptical ring seems to have disappeared unnoticed, but the red spot of 1893 at first shows signs of becoming itself transitory. The elliptical spot and the red one are both near spot, minus nearly equal to all its colour, seems still to be visible, or at least traceable, but there is distinct evidence that it has in some way changed its position. It may be that they occupy the same position in longitude which it did when first discovered, and for many years afterwards. That is all well enough; though I must confess I will justify the remark that there is something mysterious about this spot, for which no counterpart can be found anywhere in the domain of astronomy. It remains to be added that though we talk about the "discovery" of spots on Jupiter, there is considerable evidence that a spot of the same shape was noticed very many years earlier : indeed, as far back as 1665, so far as I know, the only existing copy of an old sketch (Fig. 129) ascribed to Anson and Conti is a drawing of a spot. White spots have also been observed of various sizes at various times, and also occasionally dark spots, but no explanation of the phenomena has been given. It would be well if there were a good deal to learn respecting Jovian spots, and several summaries have already been put forward. Whilst it has been thought that these spots are due to the Sun's light falling upon them, regarding their period and the position of Jupiter in its orbit, the idea has been extended to the point that there is an identity in time between the prevalence of spots on the Sun and spots on Jupiter. Whether these spots stand to one another as Figs. 109-116 PLATE XXXIII Jupiter's Red Spot and the Regions near (Dunning).
II. M. II. M.
1 Nov. 19 23 23
1885, Oct. 27 28 28
1885, Oct. 28 29 29
1885, Feb. 12 30 30
1885, May 9 8 8
A series of six images showing Jupiter's Red Spot and surrounding regions. Figs. 117-128 PLATE XXXIV.
Image showing three circular images with text annotations. Image showing three circular images with text annotations. Image showing three circular images with text annotations.
Image showing three circular images with text annotations. Image showing three circular images with text annotations. Image showing three circular images with text annotations.
Jupiter with its Satellites, Aug. 21, 1887 (Transp.) JUPITER. 87 cause and effect, or whether both are indications of disturbances of comical origin from outside the solar system is a matter on which no opinion can be pronounced with our present limited knowledge. As regards Jupiter's belts taken collectively it seems not open to doubt that they have been formed at different times by distinct traces of colour, such as pale purple, or brown or orange, but that this colour varies from time to time in a way which almost im- plies that its greatest development is coincident with a maximum disturbance of the Sun-spots. This was Brewster's idea, put forth many years ago; but I am not aware that any recent ob- server has given his attention to the change from this standpoint. The satellites of Jupiter, 8 in number, have two distinct histories, so to speak; that is to say, that the newly discovered ones have a history and individual characteristics which en- tirely differ from those of the others, and these latter may be conveniently termed. The original 8 were discovered by Galileo in January 1610 as the first fruits of the application of the telescope to the observation of Jupiter. A man named Simon Marin, who put in a claim for priority over Galileo, named them Io, Europa, Ganymede and Callisto ; but this claim A diagram showing the positions of the Sun, Earth, Moon, Venus, Mercury and Mars relative to Jupiter. The diagram is labeled "Sun" at the top left corner and "Earth" at the bottom right corner. The diagram also shows the positions of the four moons of Jupiter: Io, Europa, Ganymede and Callisto. The diagram is labeled "Io" at the top left corner and "Europa" at the bottom right corner. The diagram also shows the positions of the four moons of Jupiter: Io, Europa, Ganymede and Callisto. The diagram is labeled "Ganymede" at the top left corner and "Callisto" at the bottom right corner. Page 129 S8 THE MOST INTERESTING AND FAMILIAR PLANETS. was so universally (but perhaps not rightly) considered to be fraudulent that astronomers agreed to show their opinion by igniting the satellites with a spark. I have accordingly to identify the satellites by their order of distance from their primary, designating them as I, II, III, IV. The condition of the satellites is such that they are visible only when a distinguished American astronomer, Dr. E. Barnard, discovered a 5th satellite, very much smaller than all the others, revolving round its primary within the orbit of Venus. Rather more recently, Mr. J. L. Ferrin, of Paris, France, discovered a 6th and a 7th satellite, both revolving outside IV.; and in 1890 Melotte, an assistant at the Greenwich Observatory, made the first observations of Neptune to the astronomical world. These various discoveries can be most conveniently exhibited by resort to a table as follows:
Designation Discoverer and Date of Discovery Mean Distances in millions of miles Sideral Periods in hours
V. Barnard, Sept. 9, 1892 4 h
L. Galle, Jan. 1610 6o 0 12
IIL. 96 3 t3
III. 153 7 15
Ferrin, Dec. 3, 1890 209 18
VII. 251
VIII. Melotte, Feb. 25, 1908 26 months
All these new satellites are, as may have been expected, so small that they cannot be seen even with the largest telescopes in the world. I shall therefore here dismiss them, and confine my remarks to the four old satellites. These well deserve the attention of the amateur astronomer, not simply because of the fact that they are easily visible in the most ordinary telescopes, but because they are incessantly moving JUPITER. 89 about; and their movements give rise to certain phenomena called transits or occultations. A transit occurs when a satellite is in front of a planet, either from behind Earth and an occultation when the satellite passes behind the planet. When an instance of the former phenomenon appears the observer will see, by careful scrutiny, the satellite's disc and the black spot which it leaves on the face of the planet. These appearances must be carefully discriminated, for the satellite itself is apt to escape notice, whilst its shadow is mistaken for a star. The latter may appear to have the same as a total eclipse of the sun. In a total solar eclipse the bright body of the sun is wholly concealed by the super- posed Moon. Similarly, an appearance of a Jupiter satellite behind the Sun is entirely concealed by that planet. But there is this difference: in a solar eclipse the Moon does the work, is not only opaque, but black; but in a Jovian occurrence it is not opaque at all, but white; it covers the planet, whilst it is opaque is nevertheless illuminated, because nothing happens either to weaken or put an end to the light which falls upon it; it is like a star, receiving from the Sun all its light. These phenomena obtain full recognition in the various national Nautical Almanacs, and the information given in the British Nautical Almanac is borrowed by other countries, and used by them without any further explanation to each everybody, and no further amplification of the subject is necessary here. Under these circumstances the satellites exhibit simple illuminated discs, but with adequate optical assistance it is found that they have markings or shadings of irregular shape. Comparing one with another, we find that Io has 1H1, Gomphrena has 1H1 and 1V, the finnest; but no very positive statement can be made as to I or II, or even as to the relative brilliancy of any one of the four compared with the others, for it seems certain, or probable, that all of them are subject to changes of brilliancy. There is no clear evi- 90 THE MOST INTERESTING AND FAMILIAR PLANETS. dence of their ever showing any signs of colour. W. H. Pick- hing has noted the curious fact that, twice during each revolution of Jupiter, its appearance is changed so as to exhibit a marked elliptical outline, and that its chief shading is not a band, but is forked. He thinks also that there is some sort of abnormal in the circumstances of II. and IV. as distinguished from I. Observation of the satellites of Jupiter as far back as 1675 led to the discovery that light is not transmitted instantaneously through space, but takes time to travel from one place to another. The Danish astronomer, Römer, was the hero of this. He found that the observed times of the eclipses did not tally with the calculated times, and he concluded that the light had taken more than two hours by opposite sign of error, according as Jupiter was near to or remote from the Earth. This fact led him to suspect that the varying differences in the distances was the cause of the variation in the times of eclipses. If we suppose that light travels at the distance of the planet from the Earth the longer time it occupied in the light making itself manifest to us on the Earth's surface, then, if we consider that Jupiter is about 800 million miles at a rate of 192,000 miles per second, a conclusion remarkably near the truth, considering Römer's inferior instruments, for by more modern methods, with altogether superior instruments, it would appear that Jupiter's velocity is about 194,000 miles per second being about 200 miles in defect, the true velocity being 194,000 miles per second. Jupiter's orbit around the Sun in more than 11½ years at a mean distance of 43,000,000 miles. The eccentricity of its orbit is small, so that its greatest possible and least possible distance from the Sun varies between 42,500,000 miles and 43,500,000 miles respectively. The planet's apparent diameter varies between 6°o in Oppo- sition and 3°o in Conjunction. The equatorial diameter is rather more than 85,000 miles, making Jupiter the largest planet in the solar system. **SATURN.** There are probably very few people who have any knowledge of anything scientific who have never heard of Saturn and its ring. The planet itself is so far away that even as Jupiter, to be found without difficulty when in a dark sky, shining, as it does, like a star of the second or third Magnitude. It compares, however, unfavourably with its rivals because of its small size. Though its appendage is often spoken of as "the Ring," using the word in the singular number, yet it is really a system of rings, which vary in number according to the size of the telescope used to scrutinise it. Whilst a small telescope will only show one ring, a larger one will show this one divided into two; a still larger one will show the innermost ring divided into three parts. In addition to these there is a third main ring, which is the innermost of all. Unlike the rings just spoken of, this innermost ring is not bright, but is seen only by reflection from the sun's disc, rather more than half a century ago, of the "crane ring," has not quite fallen into disuse, and is not altogether inappropriate. The cause of the discovery of this ring is rather curious, and suggests a mysterious origin and development of it. In 1838 a distinguished German astronomer, J. G. Galle, pub- lished his results on the position of Uranus, and noticed a shading-off of the innominate bright ring towards the planet. His remark seems not to have attracted any particular notice until 1850, when G. P. Schiaparelli discovered the dusky ring, and recognised it distinctly as a ring, but transparent in so far that the body of the planet could be seen through it. This dusky ring is now a recognised feature of Saturn, and it would seem to be wider and more easily visible than for- **SATURN.** 91 92 THE MOST INTERESTING AND FAMILIAR PLANETS. merly, and a division of the dusky ring into two rings has been suspected. The germ of its discovery is to be seen in Galle's new map of Saturn, published in 1830. It appears to suggest that the ring has gone through stages of development during the last three-quarters of a century. There is no trace in the writings of either of the Herschels of their having detected any traces of such a division. In 1769, when the ring was first observed, he confessed that Picard in 1763, and Hadley in 1723, saw something which might perchance be identifiable with the dusky ring. But this was not considered worthy of notice. Saturn and its system, treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call the outermost bright ring A, the innermost bright ring B, and the dusky ring C. Fig. 1 shows the general outline of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of the cusp of Saturn's system, treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as a whole, is not only a very remarkable and interesting object, regarded as a spectacle, but every 30 years undergoes interesting transformations which make it appear as though it were a living being. It is customary to call Saturn's system treated as Figs. 130-132 PLATE XXXV. Jan. 5, 1862 (Wey). Feb.-March 1884 (Heinry). Feb. 1872 (Tuerby). Saturn 927 Figs. 133-135 PLATE XXXVI. March 18, 1892 (Eiger). July 30, 1892 (Antonini). Jan. 27, 1912 (Phillips). Saturn. [9] SATURN. 93 will attain their maximum breadth. After that they will again, to our vision, become narrower. When Saturn has completed one revolution the planet will have accomplished one-half (approximately) of a revolution round the Sun, and will again have reached the condition of being seen edgeways, the sun will appear to pass between us and the rings. For the previous 14½ years we shall have seen on this side and same side of the rings, but henceforth for 14½ years to come we shall see, also continuously, for that period the same side of Fig. 136. - Ring C, March 21, 1887. Fig. 137. - Ring C, March 27, 1887. the rings; i.e., it will be the opposite side to what we had seen previously, because now the planet with its rings will have passed to the opposite side of the Ecliptic. Continuing our predictions, on or about 1928 the rings will again be seen edgeways, and then, as we shall see, of course, the opposite side of them to what we saw in 1914. Continuing our calendar of changes, the rings will, about 1935, reach the same stage identically as had been reached in 1907; that is to say, the planet will have completed three circuits of the Sun, and will start again on precisely the same suc
Fig. 136. Ring C, March 21, 1887. Fig. 137. Ring C, March 27, 1887.
THE MOST INTERESTING AND FAMILIAR PLANETS. cession of changes as that with which it had commenced in 1707, the Sun beginning again to illuminate the southern side of the planet. From the foregoing it will be clear that from now, and for several years after the first publication of this book, the planet will be at its best as observed from this country. The diagrams which have just been sketched out involve, both theoretically and practically, many incidental details too numerous to be gone into here ; but the reader will no doubt understand that they are intended to represent the true nature of the piece, but with a bundle of rings, so to speak, the effects are somewhat complicated. One of the most natural effects is that, when the light falls on one of the rings, instead of being reflected off the edge being a continuous line of light, it is a broken line. The diagrams annexed will make this sufficiently clear without any detailed explanation. The effect of this ring system is visible throughout, but with extreme difficulty when standing by itself as between $\beta$ and $c$ and $f$ and $g$, and towards $a$ and $A$, but the brighter portions of the ring system are seen more distinctly. When looking at the outer ring is reinforced by that reflected by the inner edge of the inner ring. The bright knobs at $\beta$ and $g$ represent the light of the sun reflected from the inner edge of the outer ring, and the outer edge of the inner ring, which last-named reaches us through the inter-space between the two main rings, which is often called the Canal System. One curious fact seems well established, namely, that the rings are not concentric with the ball. This is a peculiarity which has been noticed by many observers. It has been shown mathematically to be essential to the stability of the ring system; and if this feature did not exist, and if the rings did not revolve round the planet, they would collapse upon to the planet. Thus expressed, this statement suggests that the rings are solid but it is generally considered that such is not the case ; A diagram showing a planet with rings around it. SATURN. 95 on the contrary, that they are made up of myriads of discrete particles of finer, or closely compacted together, that to our re- morse they appear to be composed of a solid sphere. In this sys- tem the rings are sensibly more luminous than the planet, and is brighter than A, but itself being very bright at its inner edge. Measurements and opinions vary as to the thickness of the ring. Sir J. Herschel thought it was 30 miles thick, which would be an outside limit for the thickness; G. P. Bond put it at no more Fig. 138.—Saturn, Feb. 7, 1890. Photographed at Mount Wilson, U.S. than 20 miles; probably 100 miles is near the mark. The general dimensions may be exhibited in the following table, which represents the diameter of the ring as obtainable, being those of Prof. E. E. Barnard, put forth in 1893:
Outer diameter of outer ring Miles. 172,310
Inner diameter of outer ring 150,560
Diameter of inner ring 146,030
Inner diameter of inner ring 110,200
Inner diameter of craze ring 88,190
Width of the Cassini division 2,770
96 THE MOST INTERESTING AND FAMILIAR PLANETS. To the foregoing may be added, from another source, 18,640 miles as the distance of the ring II from the ball. That the planet is a satellite is shown by its physical appear- ance of the ball. It has certain features in common with Jupiter—that is to say, faint belts may often be seen upon it, and occasionally a bright spot—but these are very rare. Taking the planet as a whole, it was suggested by Lassell that it might be a satellite of Saturn, but this view was dis- tinguished by the North Pole. The general hue of the planet is yellowish-white, which, to the naked eye is commonly regarded as dull grey—a seeming contradiction. There exists no clear sense of the term, though its existence seems probable, from the central portions being brighter than the circumference. Theoretically it should exhibit in Quadrature a slight phase, but it must be so small that no wonder none has ever been noticed. Satellites are not infrequently identified in the sky, diversi- sions that they furnish excellent tests for telescopes. The largest is known to be Jupiter, which is supposed to be about 7200 miles in diameter. All the satellites have received names from Greek mythology—Titanus, Iapetus, Hyperion, Lapetus, Rheia, Dionis, Tethys, and Eudemos. Telescopes of the largest size are required to show Mimas, Hyperion, Phoebe, and Epimetheus—is it possible that Titan will be discovered? With the exception of Titan and Iapetus, amateur observers will not need to give much attention to these satellites. Titan may be compared to a star of Mag. 8 and Iapetus to one of Mag. 13. Both are very faint and both are in retrograde motion. Titan revolves around the Sun in 29½ years at a mean distance of 88,000,000 miles, in an orbit slightly eccentric. Its apparent diameter varies between 15° in Conjunction and 20° SATURN. 97 in Opposition. According to Barnard, its equatorial diameter is 76,470 miles, and its polar diameter 69,770, which figures imply a polar compression of $\gamma_1$. This result is not altogether in accordance with the results of previous measures which have made the compression more considerable. I find put it as much as $k$. A page from a book, likely a scientific text discussing Saturn's measurements. 7 CHAPTER VII. THE LESS KNOWN PLANETS. The Flounders of this chapter are little interest to the amateur—History of the discovery of Uranus.—Difficulties as to its orbit.—Suspensions of the theory of the planets.—The search for the ninth planet.—The searches of Adams and Leverrier.—The discovery of Neptune.—Brief account of the discovery of Pluto.—The search for the tenth planet.—First organised search for them.—Early discoveries.—Revolutions of the planets.—Their motions very numerous.—And few of them of any interest.—Their fantastic movements some particulars of the first four.—Summary respecting their orbits. THE planets which will come under our notice in this chapter are of no intrinsic interest whatever to the amateur star-gazer, who, if he tried to find them, would in general have great difficulty in doing so. He might perhaps see one of the brightest of them, which perhaps he might do, he would very quickly come to the conclusion that they were not worth the search. But, on the other hand, there is a great scientific interest, the tale of which must now be unfolded. On the evening of March 13, 1781, Sir W. (then Mr.) Herschel was examining some small stars near H Geminorum, and one of these was so faint that he could not see it with his best telescope. Thinking what he could make of it with a stronger eye-piece, he replaced the eye-piece which he had been using by one of greater power. A star thus examined by the use of different eye-pieces always retains its stellar character of rays emanating from a point; but 24 URANUS. 99 Herschel found that the object which he had under view did not behave thus, but that increasing the power increased the discusability of its nature. The object was, therefore, not a star, was, it was at any rate not a star. Apparently no suspicion entered his head that he was looking at a new planet, for the idea of this was to new planets never, up to that time, seen have entered into his mind. Finding that the object was in motion amongst the stars, he jumped to the conclusion that he had found a new Comet, and accordingly published his discovery on March 17th. But previously to this, as early as March 17, the stranger had been examined by Maksylev, the Astronomer Royal, at Herne Bay. He found that the object was a planet, and that the planetary nature of the new body almost from the first. Notice of the discovery of something having been made public the stranger was observed at various European observatories for several days before it was announced. When its movements were subjected to calculation on the supposition that it was a comet, and, like most comets, one moving with a great velocity in an elliptic orbit; but this position broke down, its course, on the parabolic theory being falsified more and more as the observations were prolonged. In consequence of this failure, when the positions of the newly discovered visitor were reached when Leseuil authoritatively announced that the object which astronomers had been following was not a comet but a planet, hitherto unknown, revolving round the Sun in an elliptic orbit. This announcement came as a shock, in a certain sense, to many people, because it seems to have been thought that the number of known planets was seven. It is true that Uranus, recognised a? from the earliest ages? was a perfect number which it was almost an outrage to challenge. A long controversy, which was not really finally closed till the middle of the The Sun, Mercury, Venus, the Earth, Mars, Jupiter, Saturn. The Sun was always, in early times, considered a moving body. 100 THE LESS KNOWN PLANETS 19th century, arose as to the name to be given to the new planet. Herschel, by reason of the fashion of the times, proposed to call it "the Georgium Sidus," a suggestion naturally not very acceptable to foreigners, nor indeed very reasonable. The French proposal, put forth either by Lalande or Laplace, instead of "Georgium Sidus" was "Uranus." This view has a large preponderance of opinion in favour of a mythological name which would harmonise in some sense with the name of the planet itself. But Uranus is not a name which can immediately settle the matter, and Neptune, Astraia, Cybele, and Urania all had their supporters. Finally, however, the last of these names, urged by the German government, was adopted. The question as to the English mind even in things astronomical was solved by the fact that the names "Herschel" and "Georgium Sidus" in one shape or other were kept up for a very long time. The name "Uranus" did not disappear from the Nautical Almanac until the volume for 1850 published in 1846. The actual name used for many years was "Georgium Sidus," but this was changed to "Georgium Sidus," which only lasted a very few years after 1781. The question, Did anybody catch sight of Uranus before Herschel? naturally suggested itself to astronomers; and search amongst old manuscripts and old books was made with a view to it being ascertained that the planet had been observed on 20 occasions between 1690 and 1771; by Le Monnier, in 1735; by Bode in 1766; by Bode again in 1770; and by an astronomer possessed a methodical, orderly mind it seems almost certain that he could have anticipated Herschel in determining the planetary position. But it must be remembered that such an anticipation was not at once an orderly mind, if we may rely upon Arago's statement that he had once been shown by Bouvard one of Le Monnier's observations of the planet. The physical appearance of Uranus, owing to its great distance from us, and small apparent size at its best, need not URANUS. 101 detain us. Suffice it to say, therefore, that belts and spots on it have been suspected by observers with telescopes sufficiently powerful to grapple with it. It has also been thought to have some connection with the planet Saturn, and even with the Sun. Sir W. Herschel thought he had discovered 6 satellites as belonging to Uranus, but it is now recognised that only two of these were genuine discoveries. Two other satellites were found in 1847 by Lassell and O. Struve respectively, and the assured number is now 5. These have been named Ariel, Umbriel, Titania, and Oberon, or "the four daughters" from the planet, reckoning outwards. Uranus was first observed by Halley rather more than 84 years at a mean distance of 1,781,000 miles. The orbit is somewhat less eccentric than that of Jupiter. Its apparent diameter varies but slightly, and may be taken at something under 4", the rest being due to its great distance. This is a circumstance which had to be solved in connection with Uranus was the choice of a symbol for it. The one in use is a composite affair embracing a capital H, the initial of Herschel's surname, and the German word "neptun," "neptune," which does not differ much from the symbol in common use for Mars. The next section will bring the name of Uranus before us again in a very striking connection. NEPTUNE. The story of the discovery of the planet Neptune has often been told, but it will be well to give a summary of this volume would not be complete without the story being told again, even if only in a concise form. It involves, indeed, the history of Uranns, some part of which must be given as a preface to the story of Neptune. It has already been stated that Uranus had been observed on numerous occasions before the official date of 102 THE LESS KNOWN PLANETS. its discovery by W. Herschel, and that these observations began as far back as 1690. It is difficult to form any conclusions, in calculating the orbit of a new planet or comet, to base their calculations on as long a chain of observations as possible, and from the undoubted fact that when they began to make their path was unknown. Surely, then, if they start their chart from an early a date as 1690, they had great hopes that very trustworthy details of the orbit would soon be evolved. The man who took this view was the French astronomer, Jean-Étienne-Désiré Bouvard, who in 1821 produced his first detailed results, was obliged to confess that those results were very unsatisfactory. It is true that the observations made before 1780 and the observations made in 1781-1820 would not harmonise with those made during the 91 years prior to 1781. He thought only of one way of getting over the difficulty, and that was by the successive process of rejecting all the earlier observations as worthless. For a while this seemed to remove all difficulties, and the conclusion was drawn that the cause of the perturbations was then recent observations, appeared to fit in quite satisfactorily with the observations then being made. But this happy state of things only lasted a few years. For some time afterwards it appeared that other causes ought to have been occupied in the heavens for Uranus according to Bouvard's theory of the character of its orbit and the places in which, by observation, it was found to be situated. This theory seems to have had some influence which at one time pushed it forwards and at another time pulled it backwards in its orbit. At last it was discovered that there was some cause at work which disturbed the planet's movements, and the conclusion was eventually arrived at that the cause was some unknown planet revolving round the Sun in an orbit outside that of Uranus. An English amateur, Sir Alex. F. Herschel, seems to have been the first to put forward this idea. NEPTUNE. 103 a positive form, which he did to Professor G. B. Airy, the Astronomer Royal, but who had been Professor of Astronomy in the University of Cambridge. Other astronomers accepted the idea, but the first to take over action was a young Cambridge Undergraduate, J. C. Adams, who had been working on the problem since 1841, when he was only eighteen. Lack of time prevented him seriously starting his researches until 1843. He carried them on for 14 years on the assumption that the planet would be found between Mars and Jupiter. In October 1845 he forwarded to Airy provisional elements of the orbit and probable mass of a planet which would explain the irregularities in the motions of Uranus. On this side, on the theoretical side of the question, was the settlement of the question, but, most unfortunately for the credit both of Adams and Airy, the latter ignored at the time the young Cambridge student's work. The scene now changes for a time to France. In the summer of 1843 a young Frenchman, U. J. Le Verrier, of Paris, took up Adams' work and published his first paper on it in November of that year published his first Essay to show what was not the cause disturbing the orbit of Uranus. A few months afterwards, namely in June 1846, he published a second Essay in which he showed how the perturbations could be explained by attraction exercised by an unknown planet. He assigned elements to it, just as Adams had done 8 months previously. A few days after Adams' paper appeared in November 1843, and when he found how close was the accord both between the suggested elements and the suggested position of the planet in the heavens, as assigned by two very eminent mathematicians working independently in Paris and London, he at once announced upon what perhaps Adams' labourers were not so unworthy of consideration as apparently he had thought when they first came into his possession. At this time he communicated with Professor Challis, at Cambridge, who had the command of a large telescope suitable for hunting 104 THE LESS KNOWN PLANETS. up the planet, and Challis began his search on July 1 ; but he was confronted by one serious difficulty : he possessed no star- map of the particular part of the heavens in which it might be ex- pected that the planet would be found. He therefore had to prepare a new map, and this was a very laborious matter hindered rapid progress. However, he eventually prepared the necessary chart, and when it was ready he set to work with great energy. On August 13, at 6 o'clock, he found an object whose appearance attracted his attention. This subsequently proved to be the planet he was searching for. Further consideration showed that he had observed it, regarded as a fixed star on August 4 and 7, and that it ap- peared on August 12, and was recorded on the chart of July 30. Meanwhile, still in ignorance of what was going on in England, Le Verrier published in August a third essay assign- ing more positively the probable position of the planet in the heavens. He sent a summary of this revised information to Encke, who immediately set out to examine the heavens in and near the predicted place. Encke, fortunately, had just become possessed of a newly published map of the heavens, which promised to be found, and therefore he was not called upon to waste time in making a map for himself, as Challis had been obliged to do. Encke had with him two young assistants, whose names afterwards became famous in the astronomical world, J. C. Galle and H. L. D'Arrest. These men, under Encke's directions, set to work to prepare a map of the heavens for him. They called out by one by the stars visible in the telescope, whilst D'Arrest checked the map. This work had gone on for a century before they discovered what seemed to be a 8th mag. star which was not marked on any map. It was seen again on September 24, and having moved, was soon proved to be the planet wanted. An examination of the dates just given will **NEPTUNE.** 105 make it quite clear that the honour of the discovery was shared in fairly even proportion by England and France. According to Le Verrier, Neptune was the first planet for which the planet proved to be nearly true and substantially identical (with a slight preponderance in favour of Le Verrier), while Chaisis had found the planet, Galilei the first to recognise that the object seen was the planet. It should be added that it was not until October 1, two days after he had suspected that he had found the planet, that Chaisis published his results, and that he had not been aware of them previously. In the language of the gamester, we may with perfect accuracy say "honours divided." It is interesting to note (p. 37) before French men of science settled down philosophically to accept the verdict, which may now, however, be regarded as the verdict of the world, though even to this day one may find French writers still maintaining a depressing Adam's name connection with Neptune's discovery. The remarkable feature about it was that two men of different nationalities, working independently on different materials, each unknown to the other, should have fixed the heavens of a planet which nobody had ever seen, accurately within 2° in Adams' case, and within about 1° in Le Verrier's case. This may well end any statement of the matter in the words of Huxley: "Such is a brief history of this most brilliant discovery, the grandest of which astronomy can boast, and one that is destined to make its mark upon human existence--an astonishing proof of the power of the human intellect." After much discussion "Neptune" was the name agreed upon for the new planet. Galle suggested "Janus," but this name was disapproved of as too suggestive of the idea that the orbit of Neptune marked the entrance into the solar system from outside. And perhaps it was well that this suggested 106 THE LESS KNOWN PLANETS. alternative name was rejected, now that we seem drifting into the belief that there is another planet farther off than Neptune waiting to be discovered. Information is sadly lacking as to the physical appearance of Neptune, owing to its immense distance and small apparent size. It has been seen by several observers, but it may be said that practically we know nothing on the subject. If a ring existed it would be visible only at certain times, at the point of a semi- revolution round the Sun; so it might be mistaken for a planet, since its existence could be certainly known. The existence of one or more planets to be assured, and a second one being suspected, but here again there is a great lack of assured knowledge, and it is not a little surprising that, with the large telescopes lately brought into use, especially in America, no such planet has yet been discovered. Neptune revolves round the sun in 164 years at a mean distance of 37,000,000 miles. The eccentricity of the orbit is small. The planet's apparent diameter only varies between $2^\circ$ and $3^\circ$. Its true diameter is about 37,000 miles. THE MINOR PLANETS The discovery of the planet Uranus had other after-influences besides leading to the discovery of Neptune. The fact that the angle between the plane of Uranus' orbit and that of the Sun had been broken up upon put it into the minds of certain astronomers that, as there was an eighth planet (Sun and Moon having anciently been treated as planets), namely Uranus, why not Neptune? The actual circumstances which gave a practical start to the idea that there were more planets to be found if they were located were rather curious. A certain J. D. Titius, of Wettering, in Germany, discovered the following curious coincidences:
Titius' Law $a = \frac{3}{4} + \frac{1}{2n}$
where $a$ is the mean distance from the Sun in millions of miles and $n$ is any integer from 2 to 8 inclusive. Titius supposed that this law applied to all planets except Mercury and Venus. He also supposed that the planets were distributed along a line parallel to the plane of the Earth's orbit. This law was first published in 1766. THE MINOR PLANETS. 107 Take the numbers 0, 3, 6, 12, 24, 48, 96, 192, 384, each of which after the 3 is the next predecessor, and add to each number and we get 4, 7, 10, 16, 25, 36, 50, 100, 196, 384. Now these numbers approximately represent the distances of the planets from the Sun, taking the Earth's distance as the unit of measurement. This statement will be more clear if it is tabulated thus :
Planets. True distance from C. Distance by Bode's Law.
Mercury · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · 4'00
Venus · · · · · · · · · · · · · 7'33
Earth · 10'00
Jupiter [Ceres, not known in 1772] [7'60]
Saturn · 12'53
Titanus · 16'00
Saturnus · 25'00
[Uranus, not known in 1772] [19'81] [16'00]
Nepenthes, not known in 1772] · [8'80]
Another German astronomer, J. E. Bode, became acquainted with Titius's figures, and, adopting the idea as his own, and adding that in 1772 he had discovered a planet between Jupiter and Saturn (by the figures 8 and 16), and predicted that more planets existed and should be looked for. It does not appear that W. Herschel was influenced in any way by the foregoing figures when he first made his discovery. In 1773 Bode published his theory in a book entitled "The System of the World," in which he set forth his theory that the first fruits were the planets Ceres, Pallas, Juno, and Vestia. No more seeing that it was for forthcoming, the work was abandoned in 1816; but a Prussian amateur named Hencke, at Dresden, took up the work on his own account about 1820, but with no immediate success. 108 THE LESS KNOWN PLANETS The discovery of Neptune in 1846 infused new life into the movement for hunting unknown planets, of which indeed, afterwards named Astraea, had been found on December 8, 1843, by Hencke at Dresden, whose single-handed labour has just been mentioned. The year 1846 produced none. Three were found in 1847, two in 1848, one in 1849, and two in 1851. Thereafter the discoveries became much more rapid, and by the end of 1856 a total of 62 had been recorded. In 1857 the number up to 111; and since then they have grown with almost equal rapidity, so that now (1860) the total exceeds 700. The system of looking for them has latterly been materially altered. For many years after the search was first begun it was carried out very much on the lines on which the search for Neptune was conducted, namely, byocular comparison of the stars with those of known position; but this method is now abandoned in all localities; but of recent years the extensive introduction of photo- graphy has greatly facilitated the discovery of new planets. I am aware that some astronomers have expressed surprise at this continued. The actual interest attaching to these bodies is in nearly every case nil, and the labour involved in keeping pace with their record and in calculating their orbits is out of all proportion to its value. But the fact that these bodies appear to be the opinion of astronomers generally is shown by the fact that practically the whole work is now concentrated in Copenhagen, where no less than twenty-five new planets have been discovered during the last three years. Under these circumstances, I shall sum up in very concise form the rest of the information which I shall give. It will excite no surprise that these planets are in a constant state of change. It is only within a few years ago that one is found by having imprinted itself on a photographic plate ; the question at once arises, Is it a new one? or is it an old one which, having passed through a period of obscurity, has now reappeared? Here we are ending with the astronomical author who wishes to make an accurate enumeration of these planets. It may also THE MINOR PLANETS. 109 be added that of those which have been found and duly enrolled no fewer than sixty are now ticked off as "lost"---very likely because they have been lost to view by their eccentric positions at rediscovery brought into their positions with their position years ago, and so proof of their identity may never be attainable. These objects have borne various generic names. The "Minor Planets" is the name given to them by the French astronomer, Lalande, whilst the name first proposed for them by Sir W. Herschel, A diagram showing the orbits of asteroids around the Sun. Fig. 139.--How Minor Planets are recognised as such. "Asteroids," though no longer recognised by the scientific world, is nevertheless a designation not unfrequently met with. It was originally applied to the bodies under the name "Planetoid." As regards their individual names, as the out- set names taken from the mythologies of ancient Greece and Rome, together with the old Latin names, in some cases, of the places of discovery, were almost exclusively employed, but of recent years, reasonable names having become exhausted, 109 110 THE LESS KNOWN PLANETS. invented and made-up names, many of them of the most ridiculous and fanciful character, have been chosen. For instance, the name of the planet Uranus, which will often not bear investigation from the standpoint of dignity and etiquette; for instance, the planets Lumen, Bertha, and Zella are said to belong to the daughters of a well-known French astronomer. The difference between the obtaining of the holding get of the older ones is sufficiently shown by the successive deterioration which has taken place in the size of these bodies. Thus, in 1781, when Uranus was discovered, its brightness of the first reckoned in star magnitude was $8\frac{1}{4}$; of the second ten it was $\frac{9}{4}$; of the third ten it was $\frac{10}{4}$; of the fourth ten it was $\frac{11}{4}$; and of the fifth it was $\frac{12}{4}$. Its average has progressively gone down, and I suppose that no one can find which is brighter than the 13th or 14th magnitude—a sufficient justification, I think, for saying that they are not worth naming. The 4 oldest and Eros are really only those in the slightest degree worth consideration. Ceres is sometimes as bright as a star of the 6th magnitude; it is very near the Earth at times, and has been thought to possess an atmosphere. Pallas, when nearest the Earth at Opposition, is of the 7th mag., and is of a yellowish tinge. Juno is of a yellowish tinge and reddish. Vesta is of a yellowish tinge of the last, and occasionally reaches a 6th mag., shining with a light which some consider to be pure white, while others sacrifice to it a yellowish tinge. Of all these bodies, only two deserve mention—Minor Planets, the only one which has any intrinsic interest or importance is Eros. The annexed diagram, Fig. 140, shows the fact that Eros is very near the Earth, and on that account is available for enabling us to ascertain the distance of the Earth from the Sun, and it has been so used accordingly. Unfortunately, its existence was not known on the last occasion, in which it was at its nearest distance to the Earth, which was in 1894, and it A diagram showing the relative positions of Eros and Earth. THE MINOR PLANETS. 111 will not again be at its least distance from the Earth until 1924. As regards their sizes, Barnard has given the following figures for diameter: Ceres 520 miles, Pallas 304, and Vesta 333. A diagram showing three concentric circles representing the orbits of Mars, Eros, and Earth. The innermost circle represents the orbit of Mars (MARS 333), the middle circle represents the orbit of Eros (EROS 127), and the outermost circle represents the orbit of Earth (EARTH 100). Fig. 140.—The Orbits of Eros, Mars, and the Earth. 211. Except, perhaps, Juno, Hornstein thinks that none of the others are larger than 25 miles in diameter, and most of them much less—from 15 to 5 miles. One remarkable fact about these planets is that their orbits 112 THE LESS KNOWN PLANETS. are in many cases much more inclined to the Ecliptic than any of the orbits of the older planets. Hence the term "ultra- circular" planet is applicable to them. Many orbits are eccentric to a very extreme degree ; No. 699 seems to have the most eccentric orbit, the eccentricity amounting to 0° 38'. The aphelion distance is 147,255,000 miles and its perihelion distance 292,871,000 miles—remarkable extremes. The next most eccentric orbit is that of No. 699 (unnamed), in which the eccentricity amounts to 0° 38' 10". The most inclined orbit is that of Pallas (2), in which the inclination amounts to 34° 44'. The third most inclined is that of Orrut, in which the inclination amounts to only 26°. Perhaps it will appear hereafter that there is one other planet with an inclination greater than this, 189°3, whose inclination is believed to be only 2°. The planet nearest to the sun is Eros (433), which revolves round the sun in about 5 years. The honour of being farthest off rests with Hector (624), whose period is 121 years. Hector has, as its nearest neighbours, Achilles (583), Patroclus (617), and Nestor (659), all three of which are nearer than Hector. After the discovery of Pallas, Olbers suggested that Ceres and Pallas might be fragments of some larger planet shattered by some great catastrophe. The idea sounds plausible, and could be made out, but is considered to be impossible on mathematical grounds. CHAPTER VIII. ECLIPSES. The Principles of eclipses—Other kinds of phenomena—Two ancients—The difference between the Sun and the Moon—Total eclipses—Partial eclipses—Annual number of eclipses.—The Solar eclipse—The lunar eclipse—The eclipses considered—the accompaniments of a large partial eclipse of the Sun—The appearance of the Moon during this eclipse—This—the darkness—the fall of temperature—the red flames, etc.—The appearance of the Sun during this eclipse—The Moon's shadow—Shadow-bands—Buckets of light—The Corona, a kind of ring around the Sun—The corona of the Sun—Coming eclipses—Eclipse expeditions.—Lunations of the Moon—The moon's phases—The moon's motion about the Sun.—Incident in the South African War—Transits of Mercury and Venus across the face of the Sun—Transits of the planets and eclipses of the satellites of Jupiter.—Oscillation of planets and stars by means of their motions in space. THOUGH the title of this chapter is given as "eclipses" simply, the reader will find, when he gets towards the end of it, that it includes some other phenomena which are of kindred character, and which are technically known as "Transits" and "Lunations." The word "eclipse" usually brings to one's mind certain occasional events which are specially connected with the sun and moon. But there are many other phenomena concerned, as are in the highest degree simple; but, simple as they are, it is strange how little they are understood even by people of education and position, as the two following anecdotes will show. 8 112 114 ECLIPSES. Some years ago—less than twenty—there lived in the town of two sisters, who were recognised as cultivated and well-educated women. They had prepared to watch an eclipse of the Sun, and on the appointed day, at another day, according to the customary civil reckoning ; that is to say, it began late in the evening of one day, and ended after midnight of the next day. Accordingly, the almanac gave the date as we will say, December 21, 22. Through some mischance the sisters failed to begin to watch the eclipse on the evening of the 21st, and continued their observation until the morning of the 22nd, because the almanac says that it will happen on the 21st and on the 22nd. The following anecdote concerns the eclipse of the Sun of August 28, 1903. A royal personage then — said to be a gentleman of her suite, "I want to see the eclipse today; please send me a telegram with directions where I can go, and call me at the proper time out on to the terrace." Of course she received a suitable answer, which included the words, "You must be ready at ten minutes to 11." The queen was then sent by her servant to look up her seat on the terrace. The gentleman sent a very pressing message into the house, with only result that he found an answer in the form of an irritable remark, "I'm coming! why are you in such a hurry?" Which not unnaturally evoked the reply, "I'm not in a hurry, ma'am; but they're in such a hurry, and you are likely to be in a hurry also." This is a typical feature of it. Eclipses, commonly so-called, are either of the Sun or of the Moon; and according to the degree, considerable or inconspicuous, they may be called total or partial. Eclipses of different specific names. Eclipses of either luminary may be either total* or partial*, whilst an eclipse of the Sun may also bear a third name : it may be *annular.* To understand the general principles of eclipses should not Figs. 140 and 140a PLATE XXXVII AN ERUPTIVE PROMINENCE. A QUIESCENT PROMINENCE. "Red Flames" on the Sun, now generally termed "Prominences." A close-up view of a prominence, with a star visible in the background. A different angle of the same prominence, showing its structure more clearly. [API_EMPTY_RESPONSE] ECLIPSES OF THE SUN. 115 be a difficult matter, bearing in mind that eclipses of the Sun and eclipses of the Moon depend upon totally different principles. The Moon, in the course of its monthly journey round the Earth, passes, at the stage of New Moon always, not far from the Sun, travelling either higher in the heavens or lower down in them. It is only when the Moon is at these two occasions it may happen to pass quite in front of the Sun. This will result in an eclipse of the Sun. The eclipse will be total if the Moon covers all or nearly all of the Sun ; if not, it will be annular if the Moon, though centrally placed in front of the Sun, is not large enough to cover the whole of the Sun ; or partial if the Moon is too small to cover any portion of the Sun or the lower portion. Something also depends upon the position on the Earth of the observer. One observer, standing on one side of a line joining the centre of the Moon, and the centre of the Sun are all exactly in the same straight line. A B. will therefore see a central and total eclipse. Another observer, A. B.'s brother, whom we will call B. B., is on the Earth in a latitude several hundred miles more northerly or more southerly than A. B. To such a one the Moon will appear smaller than to A. B., and he will therefore only see the Moon passing over the southern or the northern part of the Sun. He will therefore only see a partial eclipse. If the Moon were always at the same distance from the Earth, and Earth and Moon were always at the same distance from each other, then every eclipse would be total, and would last for ever. But this is not so; for although they are always at the same distance from each other, yet they are not always covered with each other at exactly the same time, but sometimes they are covered for some time together, and sometimes they are covered for some time apart. But the distances referred to are not always the same; they *Cause it is only an amusing one.* 116 ECLIPSES vary considerably. It follows therefore that if, when the Moon is nearest the Earth, the Sun should be at its farthest possible distance from the Earth, the Moon would have its greatest visibility, and the eclipse would have the effect of making the overlap during totality the largest possible, and therefore the duration of the Sun's invisibility the longest possible. But this cannot happen, because when the Moon is at its nearest distance from the Earth, and the Sun at its smallest, the Moon would look its smallest and the Sun its largest. Under such circumstances, there could be no total eclipse of the Sun; for the whole of the Sun ; and such are the circumstances under which the eclipse would be annular to an observer viewing it from such a latitude on the Earth as would make the Earth, the Moon, and Sun appear in a straight line. Another consequence follows from the ever-varying position of the Moon as regards its distance from the Earth. An eclipse may take place when the Moon is near to us, but when it is far away from us, its distance from the Earth may have varied so that it has become smaller and therefore looks smaller, and an observer on the Earth will see the centre of totality at a time when that part of different diameter of the Moon has been diminished, so that it is no longer large enough to cover--the whole of the Sun. To such an observer the eclipse will rank as either a partial or semi-total one, such was the eclipse of April 17, 1912. Turn we now to eclipses of the Moon. Though, so far as names are concerned, they are called "total" or "partial," yet their totality or partiality depends upon principles quite different from those which bring about the same nominal results in the case of eclipses of the Sun. The Earth and the Moon being both illuminated by the Sun, both, of course, cast a shadow into space, just as every opaque object put in front of a source of light has its shadow thrown behind it. If, therefore, at the time that the Moon is in that position of its orbit known as the Opposition (when it is on the PLATE XXXVIII Fig. 142
Image of a lunar eclipse progression. June 6, 1894. June 5, 1899. May 28, 1903.
Image of a lunar eclipse progression. Aug. 10, 1905. June 26, 1908. April 17, 1918.
Image of a lunar eclipse progression. Aug. 21, 1914. Feb. 7, 1916. Nov. 22, 1919.
Image of a lunar eclipse progression. Nov. 10, 1920 Nov. 8, 1921. Mar. 26, 1922.
Solar Eclipses visible in England, 1891-1922. A series of images depicting different phases of solar eclipses. Fig. 143 PLATE XXXIX. A night sky with a total eclipse of the Sun. The Sun is partially obscured by the Moon, and the Earth's shadow is visible on the Moon. Trees and a body of water are visible in the foreground. Saturn. Venus. Mercury. Earth. Mars. Total Eclipse of the Sun at sea in the Washak Valley, near Wisconsin, U.S., Aug. 7, 1880. [14] ECLIPSES OF THE MOON. 117 meridian at midnight), and Moon, Earth, and Sun happen to be exactly (or nearly) in the same straight line, the Moon, in its progress round the Earth, will plunge into the Earth's shadow, and will appear dark. In this case, the Moon will wholly or partly cast shadow on the inhabitants of the hemisphere which is turned away from the Sun. The Moon may also be seen in the sky without any shadow, may either become completely invisible or signs of its presence in the sky may be obtainable from the fact that a faint reflection of the Sun's light is seen on it, and it keeps it dimly in view. This visibility or invisibility has nothing to do with the principles of the eclipse; but I shall discuss the matter under another head later on. It is only necessary to say here more fully into details respecting these eclipses. If the orbits of the Earth and the Moon were in the same plane all eclipses of the Sun would happen to occur every month at about the same time; but an eclipse of the Moon would also happen every month at the epoch of Full Moon; but the Moon moves round the Earth in an elliptical orbit, and therefore makes an angle of about 5°, and therefore it is only on occasions that Moon will be found immediately in front of the Sun so as to bring about an eclipse of the Sun, or immediately behind the Earth (because of its elliptical orbit) so as to bring about an eclipse of Moon. The effect of this inclination, coupled with certain other disturbed conditions which subsist with respect to the Moon's orbit, causes eclipses of both kinds to be rare; eclipses in the course of a year are limited, and vary. There must always be two, and cannot be more than seven, eclipses in a year. The number of eclipses depends upon the position of Sun. In the case of the seven, five of them may be solar, in which case only two can be lunar, though under no circumstances can there be more than three lunar eclipses in one year; and in some years there may be none at all. If the almanacs for a few successive years are consulted it 118 ECLIPSES. would seem that the succession of the eclipses is very irreg- ular, yet that is not so in reality if the almanacs of 18 successive years are compared with each other. The number of thrice that period, or 54 years, is examined. If either or both of these things are done it will be found that eclipses recur almost in the same order every 18 years 10 days, or in every 36 years 20 days. This fact was known more than 3000 years ago to the Chaldean astronomers. They called the scheme the "Saros", and they made use of it for predicting eclipses for any number of years in advance. It does something more, for it not only enables the amateur to predict eclipses for himself, but also enables him to say in advance when he may expect a solar eclipse to pass across the Earth. If we take any given eclipse, say of the Sun, visible at any particular place, a nearly similar eclipse will occur at another place within about 18 days, and again after 10 days later, but the locality will be a certain number of miles different, and S. of the previous line of central eclipse. The first great solar eclipse visible in Europe was the eclipse of the Sun visible in the north of Norway on August 19, 664, at the hour of 4.30 in the morning. This eclipse will recur on August 21, 1714, but the central line, still in Norway, will be at the hour of 4.30. It is evident that this method will be much more convenient, because it will be nearer the break- fast-hour of most people. The gradual transformation of the exact position of the central line into a general line by taking following particulars of the eclipse of the Sun of June 1295, when it appeared at the North Pole. In 1357 it had gone southwards to Denmark and Sweden; in 1425 it passed over Europe; in 1430 it was visible all over Europe; at its nine- teenth appearance in 1601 it was central in London ; on May 5, 1818, it was also visible in London, and was again nearly central in the metropolis on May 15, 1826. At its next ap- pearance on May 26, 1824 the central line passed over North ECLIPSES OF THE SUN. 119 Africa; on June 6, 1872, it crossed France; on June 15, 1893, it crossed North Africa; on August 20, 1894, on June 28, 1904, it was central in Mexico, Florida, and across the Atlantic to Senegambia. At its thirty-ninth appearance on August 10, 1909, the Moon's shadow will pass S., of the Equator, and at its forty-first appearance on March 23, 1920, it will cross Europe, Africa, and Asia, and visible only in South America. At every subsequent period the eclipse will go more and more towards the South Pole. On September 30, 2665, it will go off at the South Pole of the Earth, and therefore the series will have ended. Thus far we have been considering eclipses of the Sun and Moon separately; but we must now deal with solar and lunar eclipses separately, because they differ so much in the details relating to their obscurity. The former are caused by the Moon passing between the Sun and Earth; the latter by the Sun passing between the Earth and Moon. An eclipse of the Sun in cases where only a portion of the Sun is obscured offers really no features of interest unless the portion obscured exceeds one-third of the diameter of the Sun's diameter. When this amount of obscuration occurs there are a few subsidiary occurrences calculated to interest the student of nature; for instance, the reduction in the sunlight available to plants during an eclipse may be considerable though not a cloud is visible, yet the sky puts on a dark, lurid appearance suggestive of a severe thunderstorm being at hand. The reduction in light due to an eclipse may amount to the amount of $^{5}$ Fahrenheit°, or even more, and the personal sensation of chilliness experienced is even greater than the thermometer implies. Birds distinctly manifest their keenest sense of temperature when they fly about during an eclipse; those that do not definitely go to roost, they are evidently uncomfortable and suspicious. If any trees near are in leaf images of the crescent Moon may be seen through them; indeed even a book, laid on the ground so that images of the Sun may pass through the foliage. Finally, the maximum phase is 120 ECLIPSES. accompanied by a sudden gust of wind. All these phenomena were seen in different parts of England on the occasion of the large eclipse of April 17, 1915. It is when a total eclipse of the Sun happens that a solar eclipse shows to the greatest advantage, many of the features marked by the sun's rays being thrown into relief. The excite- ment of the spectators being greatly accentuated by the rapidity with which the transformations take place, and the intensity of the light, it is not surprising that we find here speaking of eclipses of the Sun observed by educated and sensible people, who know all, or at any rate something, about the matter. But when the spectators comprise ignorant natives, or even savages, such as the Aborigines of Australia, a total eclipse of the Sun is usually the occasion of remarkable scenes in which alarm and despair and anger are intermingled. From this point of view I have selected some of the most striking scenes. I select the following as typical of many such narra- tives. But the first quotation will show that we need not go so far as to the lands inhabited by Indians for an example of an eclipse passage. The Earl of March quotes from a letter written by a certain Sir Thomas Prendergast, from Panglase, under date of August 30, 1869: "I would have spun out a few lines more in relation to the eclipse, such as the care taken to get in all the hay before it; prayers said in churches, preparatory and preventive; and much more." What happened on the occasion of the total eclipse of July 29, 1875, was thus described in an American newspaper by a spectator resident at Fort Sill, Indian Territory : "On Monday last we were permitted to see the eclipse of the Sun in a beautiful manner. We had made ample preparation, laying in a stock of smoked glass " "A Duke and his Friends" (London, 1915). PLATE XL. Fig. 144 The Solar Corona, July 29, 1878 (J. P. Murphy). A black and white photograph of a solar eclipse with a bright corona surrounding the darkened sun. Figs. 145-146 PLATE XLI. The Solar Corona, August 29, 1886 (Harvard Annals xviii.). The Solar Corona, Dec. 22, 1889 (Perry). TOTAL ECLIPSES OF THE SUN. 1 2 1 several days in advance. It was the grandest sight I ever beheld. The crowd of spectators, numbering hundreds of them, threw themselves upon their knees and invoked the Divine blessing; others flung themselves flat on the ground, face down, and covered their eyes with their hands, in order to avoid terror. Finally, one old fellow stepped from the door of his lodge, and, after a few moments' hesitation, addressed the multitude with a few unintelligible words, and, raising his arm, took direct aim at the luminous, fired off his pistol, and, after throwing his body into the air, fell dead on the ground. The spectators retreated to their own quarters. As it happened, that very evening a great comet appeared in the heavens, and the glorious orb of day once more peep forth, and it was unanimously voted that the timely discharge of that pistol was worth all the other honours which had been paid to and saved them from the public inconvenience that would have certainly resulted from the entire extinction of the Sun." We will now go back to the general concomitants of a total eclipse of the Sun as they present themselves to a rational observer, who can deal with the matter in a calm and philosophic manner. When the Moon passes between the Earth and its forward limb has broken in upon the Sun's disc, nothing remarkable is to be noted until the Moon's movement has so far progressed as to have passed over the horizon and commenced its course across the disc. While part of half the Sun has been obscured by a fall in the temperature of the air around the observer will begin to feel "the." The next thing which will be noticed will be a change in the colour of the sky. The ordinary blue will become much deeper, soon passing into a dull dark colour which will eventually reach purple. The eye is thus prepared for what is about to happen; changing the sky nearly, but not quite, down to the horizon; for the lovelier strip, so to speak, of the canopy reaching actually to the horizon is not purple, but orange, more or less, in colour, which hue is due to the fact that the Sun's light which reaches the observer from the horizon has to pass through a very thick 122 ECLIPSES. stratum of atmosphere which absorbs much of the violet light of the spectrum. This will indicate that the total phase is at hand, and that instant and the two or three minutes (according to circum- stances) which will follow constitute the high-water mark of the phenomenon. The duration of the eclipse may vary greatly, but still might, according to theory, reach such an extreme as seven minutes, this extreme never is reached, and from two to four minutes being usual during most eclipses. These have been observed during recent years. This means that an immense amount of work, such as photographing and note-taking, has to be compressed into a very limited amount of time, and amid The first feature which suddenly springs into view are jets of Red Flames, now more generally called Prominences, which extend from the Sun's disc towards its limb in all directions. It was at one time supposed that these Red Flames were only to be seen during total eclipses, but modern instruments and methods of observation have shown them to be visible even when far as their positions and shapes are concerned. These Red Flames are now recognised to be masses of incandescent gas mixed with other gases, one of which, now called helium, Almost coincident with the appearance of the Red Flames, or even before them, numerous beads of light spring up along the edges of the Moon. These are known as "Baily's Beads," after Mr. Baily's description in 1836. Their explanation is somewhat obscure. It has been supposed that they are outstanding spots on the surface of the Moon, but this is not true. All the adjacent mountains project far beyond the smooth circular outline of the Sun's disc, which is no longer visible as a con- tinuous body. The light which causes these beads comes from the Sun itself, but the optical phenomenon known as the irradiation of light is no doubt a contributory cause. TOTAL ECLIPSES OF THE SUN. 123 The most important feature of a total eclipse of the Sun is the Corona, but there is so much to be said about this that it will be presented separately. It is necessary to give a necessary details of a total eclipse before embarking on the Corona. The first and most obvious proof that the moment of totality has been reached is the darkness which accompanies it (probably that of night) which prevails everywhere, darkness usually so great as to necessitate the use of lamps for reading clocks and watches. This intense degree of darkness is not, however, invariably experienced at all places during a total eclipse. The cause always be foreseen or explained the darkness is very much less intense than the typical darkness just alluded to. The two eclipses of 1860 and 1870, both of which were total, were marked by both these characteristics. During the eclipse of 1860 the darkness was, I apprehend, normal, but in 1859 the darkness was so great that it was necessary to use lamps. The evident cause was the prevalence of so much cloud all over the sky, and probably that would be the explanation of all cases in which the darkness was not very intense. But incidentally the cloudiness may have been due to some other cause having to be taken into account. The duration and the extent of the apparent overlapping of the Sun by the Moon, whether much or little, would certainly affect the intensity of the resulting obscuring. The shadow cast by the Moon on the Earth of course moves progressively along the line of contact between Sun and Moon. This shadow can be seen and followed by an observer suitably placed. The words "suitably placed," in this connection, mean that the spectator occupies an elevated position, say on an eminence or on a tower or church-tower—that is to say, occupies some coign of vantage which enables him to scan a far-distant horizon. During this he will be able to catch sight of the shadow moving up to his own position, sweeping over him momentarily, and then rapidly pass- ing off in the opposite direction. The necessity for an observer 124 ECLIPSES. being side aware who is desirous of catching sight of this shadow will be uninterested by the statement that it travels at the rate of three miles per second. Another very curious and interesting feature of a total eclipse of the Sun is one which has only come into prominence of late years. This is the phenomenon known as the corona, or visible a few minutes before totality, say five. They are wavy streaks of light and shade which dance across the landscape, and are best seen if the observer can so place himself as to face an object on which he can see his own shadow. The corona is due to receive the shadows as they pass along. Nothing is known of their cause, or of any laws which regulate them. They vary at different times, in appearance once, in breadth, and in the speed with which they travel. One other thing may be mentioned : the brushes of light which precede the corona are those which are cast by the rays of the dark Moon opposite to the disappearing crescent of the Sun. It does not seem that these brushes of light are directly associated either with the Corona or with Italy's Beads, or indeed with any other object in the heavens. I have no doubt that, on this point, it is true, however, that there is an entirely independent existence, and I am not acquainted with any well-considered explanation of their origin. The fact that they appear to follow the path of the total eclipse of the Sun on which every observer, as a rule, concentrates his attention, unless he is officially turned off to some thing else. Briefly described, the Corona is a broad ring of light seen around the disc of the Sun during its passage through lunar shadow during totality, and disappearing on the return of the Sun to visibility. It is usual to consider the Corona in a twofold aspect : first, as a ring of light surrounding the disc of the Sun ; and secondly, as a "outer Corona." The two together constitute a broad bright ring of light varying diameter, or perhaps it will be best to consider the inner Corona as a mean averaging 30 degrees in diameter while the outer Corona varies from 1, 2, or 3 degrees from the Sun, a which distance it generally has out its more or less FIG. 137 PLATE XLII. A solar eclipse photograph showing the Sun's corona during a solar eclipse. The Sun is partially obscured by the Moon, with a bright ring of light surrounding the darkened disk of the Sun. The Solar Corona, 1898 (C. Michie Smith). 124] FIG. 148 PLATE XLIII The Solar Corona, July 28, 1903. 123 THE CORONA. 125 circular outline, its edges developing into long rays or streamers of varying length, and stretching from various parts of the Sun's circumference to the horizon. The appearance of the Corona, as it is well understood that the Corona belongs to, and is an appendage of the Sun, but looked at merely from the sight-seeing point of view it might equally seem to be a ring around and belonging to the Moon, was first noticed by the ancients, and was called a lunar appendage, and it was only during recent years that it has become certainly established that the Corona, whatever it is, belongs to the Sun. It is now generally admitted that it is best understood by a careful examination of the accompanying illustrations, which represent its appearance at many different distances from the Sun, and at different times of day; by resort to hand-drawing, but the majority due to photography. By far the most interesting recent discovery connected with the Corona is the fact that its variations in shape depend upon an annual cycle, which has been discovered by careful study and understood. The law, stated boldly, is that the outline of the Corona varies in a most marked degree according to whether the Sun is in conjunction with Mars or in opposition with epoch of maximum or an epoch of minimum Sun-spots. In the former case the general outline of the Corona is roughly circular and compact, whilst in the latter case it is not only exceedingly irregular in form, but also very much larger than when appear ing 2° or more on each side of the Sun in prollegation of the solar Equator, accompanied by narrow flames of light at either pole. Speaking generally, I think we are entitled to assume that the Corona is something in the nature of an atmosphere sur- rounding the Sun, and that it is formed by some process of evaporation and the uncertainty and irregularity of its streams, and its undoubted connection, in some way, with the presence or absence of Spots on the Sun render it one of the great mysteries of modern astronomy; the perfect unravelling of which has yet to be accomplished. 126 ECLIPSES. A question is often put by that well-known personage, "the man in the street," in the dual form of "What is the good of an eclipse?" and "What is the use of an eclipse?" The answer to this trouble and incuring so much expense to observe an eclipse of the Sun?" Perhaps no very direct answer can be given, and a cynical mind might take pleasure in recalling Sir George Corbet's remark on the subject, which was so often stigmatised as a "science of pure curiosity." The remark, though by no means fair or strictly accurate if applied to the scientific pursuits of the ancients, is applicable to the special subject of Eclipses. They are only observed and can only be observed to satisfy human curiosity, which desires to know what is beyond its ken. In the writings of Aristotle in this case the physical constitution of the Sun is described by Proctor in the title of one of his books as the "Ruler, Light, Fire, and Life" of the system. The history of the last 35 years in particu-lar have thrown a flood of light on the origin of those phenomena which form the accessories of a total eclipse, and have shown how they are connected with the con-stitution of the Sun. Of the special sights which present themselves during a total eclipse, beyond doubt the Corona is the most interesting and most striking. In the early days of observation it was supposed that this phenomenon was caused by the Corona was connected with the Moon or the Sun. It is now a matter of perfect certainty, as has been already stated, that it is caused by the reflection of sunlight from the Moon which has only a secondary share in the matter for the reason that its own solid body blocks out the sunlight from observers on Earth. This is proved by observing that when a ray of light which emanates from the Sun and constitutes the Corona. The question of the shape of the Corona, as connected with the prevalence of Sun-spots, is such an important one that it is worth while to recapitulate the facts in a slightly different form; thus: When a total eclipse of the Sun occurs at or FORTHCOMING ECLIPSES. 127 near the epoch of the Sun-spot maximum, the Corona takes a distinctly compact shape, with its outline of very much the same form as that of the Sun's disk. At such times, observers special off-shoots may be visible. On the other hand, when an eclipse occurs at an epoch of Sun-spot minimum, there is a marked deficiency in the breadth of the Corona at the poles, and it is only in the equatorial regions that both E. and W., the Corona throws out broad, elongated streamers, which on some occasions have been traced to a distance of 30° from the Sun. The cause of these differences is at present unknown, but the facts are unquestionable. It is interesting to note that the eclipse of 1890 was predicted by Sir J. J. Thomson, on the subject of a prediction, that it as coincided with an epoch of Sun-spot maximum, which would be elongated in the Sun's equatorial regions ; and this proved to be the case. There is no new, or even modern discovery, the record of its existence certainly goes back to 1575, and perhaps even much further than that. What is modern and new is that we now know how often the corona varies periodically, with so close relation to the spots on the Sun. It may interest the reader to hear something about the eclipses which will happen during the next few years. The following list, which follows is taken chiefly from the *Nautical Almanac*, and the *Rev. S. J. Johnson's Historical and Future Eclipse*. 1891 March, 22.—Total eclipse of the Moon, invisible at Greenwich, visible in North-Western and North-East Asia. 1913 April, 6.—Partial eclipse of the Sun, invisible at Greenwich, visible in Labrador. 1913 September, 29.—Total eclipse of the Moon, invisible in Greenwich, visible in Labrador. 1913 September, 30.—Partial eclipse of the Sun, invisible at Greenwich, visible in South Polar regions. (Mag. o'82) 128 ECLIPSES. 1914, February 24.—Annular eclipse of the Sun, visible only in the South Pole Region. 1915, March 12.—Partial eclipse of the Moon, partly visible at Greenwich in the early morning. 1916, April 30.—Total eclipse of the Moon, visible at Greenwich with a partial eclipse (Mag. o'51). The central line passes through Southern Russia, north-westwards through Norway, and southwards through the Atlantic Ocean to Greenland, and is visible only in Polynesia. The foregoing statement of the eclipses of 1913 and 1914 embraces all the eclipses of these years, but considerations of space do not allow me to give any details respecting those of 1915 and 1916. I have omitted them because they are not so remarkable as those of 1913 and 1914, either by reason of their rarity or of their obscurity, or both. I have also omitted them because they are not so important as those of 1913 and 1914, either by reason of their rarity or of their obscurity, or both. 1916, February 3.—Total eclipse visible in the Atlantic, just missing from England. This was the first total eclipse visible at all in England since 1724. 1915, January 24.—Total eclipse, visible in North America and across the Atlantic to beyond the N. of Scotland. 1908, August 20.—Total eclipse visible in Wales, Lancashire, North Yorkshire, and Durham, but total for only about one-third of its duration. This was actually the first total eclipse visible at all in England since 1724. After 1927, England will have no chance of another total eclipse until August 11, 1990, when the shadow-line will cross a part of the country. In between these two dates there will be centuries which will not see another total eclipse. But during this period there will be four following conditions presented by the eclipse of 1905 :—a such a long duration of darkness ; a locality so good as to permit observation from a height sufficient to clear the horizon ; and a locale so accessible from the shores of This is what is commonly stated, but according to the map on Oppelzer's Comme de l'Observatoire, this line does not touch England, but passes a certain number of miles to the S. and so into France. OBSERVATIONS OF ECLIPSES. 129 England as was Spain. Finally, it may be stated that on October 7, 2135, there will be an eclipse the central line of which will pass through London. Speaking generally, total eclipses of the Sun may be said not to vary very much in number from century to century, but the greater part of them have been observed by our ancestors, compared with the limited opportunities possessed by our ancestors, or even by our grandfathers, make the subject of eclipses much more familiar to us nowadays than was formerly the case. The following are some of the most remarkable eclipses observed as they have been in many parts of the world which used to be more or less inaccessible, have yielded the numerous facts which have contributed to the improvement of the theory of the Sun which have been mentioned earlier in this chapter. As regards the question of instruments, it is no longer necessary to employ any instrument whatever to see the visible sights offered by an eclipse to persons armed with only ordinary telescopes. Of course a telescope (which need not be a very large one) is necessary, or, at least, very useful for observing the sunspots and other phenomena connected with the progress of a solar eclipse. Indeed, an opera-glass, or even the naked eye, suffices to disclose many interesting features; but, to get all the details required for accurate observations, the most up-to-date fashion, a good deal more is wanted than a mere telescope. Moreover, the astronomer requires the active assistance of a photographer and of a practical chemist, to say nothing of those who can prepare and apply chemicals to them. Accordingly, the impediments of a fully equipped eclipse expedition are vastly more numerous, more heavy, and more expensive than those which are met with in the modern application of steam to railways and ships which enables astronomers of the 20th century to do the work which the scientific exigencies of the century demand. But with all these facilities, if referred to, it will easily be understood that it is no joke to organise and carry to a success- 130 ECLIPSES. ful issue eclipse expeditions from England to such far-off localities as India, or Polynesia, or the West Indies, though such things have been done at times within recent years. When, however, English astronomers in England had, in 1905, the chance of a total eclipse of the Sun no farther off than Spain, they did not hesitate to make use of it. They would be a rush to see it, which would not have occurred if it had been a question of a voyage to Java, or Tierra del Fuego. Hence it comes as something of a surprise that in 1905, although the eclipse had been looked forward to with great interest by vast numbers of English people, astronomers and non-astronomers. These may be said to have had their appetite whetted by the eclipse of 1874, when it was seen in the Azores and Portugal. But this eclipse was under the important disability that its duration was very short, only 14 minutes—a period too brief for any but the most keenly observant to appreciate. The eclipse of 1905 was due to last 36 minutes, an interval to be deemed substantial, since that under no circumstances, as already stated, can the most favourable totality last for more than 15 minutes. Therefore the probabilities were that large numbers would flock to Spain from England (and, for the matter of that, from other countries) to witness this great event. Accordingly, some account of the preparations which had to be made (including which always have to be made before total eclipses) will probably interest those who read this paper. From England the eclipse was back than a few months before the great event. Though it is rather the fashion to run down Spain and things Spanish, it must be stated, to the credit of the British Government and its officials, that owing to advance did the Madrid Observatory begin taking steps to prepare for the eclipse, first by the issue of a very good map of the path of the central line across Spain, and afterwards by the issue of a very useful pamphlet on how best to observe it. * * * Wm. H. Moulton Royal Astronomical Society, vol. ix. p. 435 ORGANISATION OF ECLIPSE PARTIES. 13 advice. These preliminary documents proved most useful to the English Astronomical Societies and private individuals who intended to travel to Spain for the eclipse observations. In all such matters there are certain very important points to be handled, to which all others must be subordinate. First and foremost comes the selection of suitable positions at possible eclipse times, whether observed in or near the central line. Infor- mation as to this had to be sought from existing records already published by Spanish meteorological authorities. These were collected, consulted, and tabulated with the following general results. It was found that there was a probability of fog and haze prevalent over the whole of the central line of Spain, at or near the actual coast-line, though this could be evaded by journeying 50 miles inland by roads or railways to towns without hotel accommodation. Still further inland, especially in the mountains, where the air is cooler, it was found that eligible positions could be selected for observing the eclipse, all the more eligible because, Burges being situated on an elevation above the sea, a fair amount of fresh air as a modern standard of comfort was obtainable. The question of temperature constituted all along a great difficulty in making up eclipse-observing parties, it being well known that the summer temperature of the S.E. of Spain is quite tropical in its character. Next after the question of temperature came that of accommodation, beds and bedding to the taste of Mr. and Mrs. John Bull being difficult to obtain, indeed almost non-existent in Spain. The British Astronomical Association was asked to say, about a year and a half before the appointed day—the British Astronomical Association nominated a special committee to consider the travelling and observing arrangements which it was expedient to make. The question of travelling was dealt with first. The difficulties which it was known would have to 132 ECLIPSES. be faced in respect of the extreme heat and the general lack of comfort attending long accommodation led the Committee, in the first instance, to consider the establishment of a local accom- going steamer, which should land parties to settle themselves on different places on the S.E. coast, with Valencia as the permanent headquarters. This was done for the benefit of more, making use of the steamer, as much as possible, as a local hotel. Several steamship companies applied to one and all refused to cooperate with the Committee except on terms and conditions which were so excessive as to be prohibitive. The con- templated grand expedition in its complete form had then to be abandoned. The Committee therefore decided that persons who had given in their names to go somewhere or other were left to make arrangements for themselves as best they could. The redoubtable Cook then came upon the scene, and offered perpetual passage at a very moderate price from London to Burgois, and partly by land and partly by sea, to the Balearic Islands viz Marselles. The Committee's resolution offered to organise another party from London to Burgois at a shelter-eleter pace and cheap fares. Their number (20) was soon made up. Besides the foreigner's foreigner's attempt made, with more luck it was generally less success, to get a passage for Gijon on the N. coast of Spain, for Valencia on the S.E. coast, and for Philippeville in Algiers. The Committee, under various subsidiary observing centres generally turned on the facilities available for local travelling from the chief centre and on the question of hotels ; for, happily so far as this particular subject was concerned, there was never any serious doubt or risk about fine weather and a clear sky being assured. Observations of eclipses of the Sun differ from all other astronomical observations in a very important particular. Most observations are performed by one chief observer with or ORGANISATION OF ECLIPSE PARTIES. 133 without some assistance from a subordinate, who will perform such minor duties as calling out or writing down times as indicated by the instruments, and opening and closing shutters and slides. An ordinary observer, with or without a little help from a junior, can, as a rule, take his own time in performing the task which he has been assigned, however much he may have been hurried. Things are quite otherwise, however, when a total eclipse of the Sun is in question. There is then no opportunity for leisurely work. A dozen different things have to be done at once, and all must be done within a very short any rate, within the compass of a few minutes, which seldom exceed three or four at the outside. When an eclipse is about to occur, therefore, to make up his mind, not only that he cannot see everything himself, but that he can hardly hope to see even one-tenth of every- thing. The work, therefore, calls for much self-denial on the part of the observer. He must be willing to sacrifice any pleasure he may derive from seeing his neighbour's face, and must resolve to concentrate his mind on some one or two special points, whilst his next-door neighbour on one side concentrates his attention upon another. He must be prepared to let his neighbour giving him his mind perhaps to a fifth, or sixth, special point; and so all the expected phenomena are, by judicious pre-arrangement, shared out amongst the different members of a party. After every eclipse it is usual for the members of a party, especially if they belong to some public or State Observatory, to give each other a detailed account of what they have performed during the critical brief minutes of totality, and to make sure beforehand that each understands his share of the work. It is also customary for them to cross-trapass upon the duties of their coadjutors, or have a fiancé with his own instruments or apparatus. Prior to the eclipse of 1900 the Astronomer Royal's party at Greenwich had a grand rehearsal, which was afterwards repeated with models of sun eclipses, much to the amusement of the spectators, at 134 ECLIPSES. a meeting of the Royal Astronomical Society at Burlington House. Inspired by this precedence, one day in July 1955, the Eclipse Committee of the British Astronomical Association gathered together a number of those who intended to observe the eclipse, and carried out a very useful, though informal, exchange of ideas. The result was that each member brought his appliances at the command of each with a view of avoiding to some degree, by pre-arrangement, waste of time and waste of labour. In this way, the members of the committee found themselves up in the intricacies of French and Spanish railway travelling, and Spanish hotel life, unfolded their experiences for the benefit of others. As regards the work which was to be performed—that is, the observations which were to be made—the Eclipse Committee just named entrusted the preparation of an "agenda" to Mr. A. H. Mauder, who had been appointed to that task. It is needless to add that the work was well and judiciously done. It had scarcely been commenced when Mr. Mauder received an invitation from the Canadian Government to join them observing party, which was going to the far-off locality of Labrador, and which, therefore, rendered it necessary for him to leave England several weeks before the Spanish parties did so. At well-nigh all these places where all attempts to reach an expeditionary, wholly or partially, had failed, it was discovered that the P. R. O. Mail steamer leaving Tilbury on August 25 was due to cross the line of central European longitude at about 10 hours after noon on August 26th, and almost at the very hour, of the eclipse, and negotiations were entered into with the Company with a view of arranging that the ship should have-to for two or three hours to enable the passengers to have a leisurely view of the phenomenon. So soon as this decision was arrived at it was communicated to all PREPARATIONS FOR THE ECLIPSE OF 1905. 135 the members of the British Astronomical Association, and others who had desired to see the eclipse without incuring the expense of travelling to Spain, have been enabled to do so by the courtesy of the Spanish Government. In Spain during the hot days of August. Thanks to the officials of the P. & O. Company, the details were soon worked out. This was a very interesting experience, as it gave me an opportunity to under- stand something of the nature of the preliminary matters which had to be handled ; but my statement of them is very far from being exhaustive, for I have limited myself to matters affecting those who came to Spain. I have said nothing about what the Americans proposed to do, and the Americans always carry out their scientific expeditions with great energy and efficiency. They have done more than anything about French or German efforts. France has an Astronomical Association, run very much on the same lines as the English Association, and they have made arrangements for some co-operation might have been arrived at between the two bodies; but this did not come about, chiefly because the travelling necessities of the two nations were different. The Americans were anxious to get to Spain whilst the French were already next door. Since the eventful months of December in the eventual year 1874, when a large number of astronomers from all parts of Europe escaped from beleaguered Paris in a balloon in order to observe the total eclipse of the Sun of December 23, 1870, there have been many expeditions to all parts of the world to observe eclipses. But since that time, excepting one or two instances, no member, there has never been an instance, till the year 1905, of an expedition of astronomers and astronomically-minded people leaving England or France, and organised to observe an eclipse at a " station " on the high seas. The nearest approach to this would seem to have been the voyage for one or two in mid-Atlantic, on May 29, 1900, of the ss. *Auroral*, of the Orient Line, on its outward voyage to Australia in order that its passengers might view this most 136 ECLIPSES. phase of that day. There was, however, no set purpose on the part of the steamship company to provide this special show for the benefit of the passengers. The episode was contrived by Colonel Markwick, R.A., F.R.S., who had obtained an assurance that the steamer would cross the eclipse line at the right time. This was done by a very ingenious arrangement with the captain viewed by Mr. W. B. Gibbs, F.R.A.S., on board the Union Castle s.s. Ralston Castle off Cape Town. Nor do I think there was any set purpose in the mind of the captain of the French man-of-war Le Comte d'Artois, who, on July 28th, 1854, observed at sea the eclipse of February 9, 1704. Perhaps he hoped to be by design that the Spanish Admiral, Don Antonio Ulla, saw the total eclipse of June 24, 1787, at sea, when passing from the American to the European continent. Observations, particularly the Philosophical Transactions, 1779, concerning their early date, are extremely interesting. We have here a very full call for special notice in this place as regards the personal adventures of the observers who chose terse firms in Spain for their work, but the fortunes of the sea-going party, of whom I was one, are worth a brief mention. We sailed from Lisbon on May 20th. The observers took ship at Tiburio under the P. & O. steamer Arcadia, Captain Cubitt. After an uneventful voyage, only varied by landings at Gibraltar and Malta, we reached our station near the eventful day, August 30th, at the exact spot in the Mediterranean, not far from the Balearic Islands, in the precise latitude and longitude which it was calculated we should put on us. The weather was fine and clear; we did not fail; we everything most successfully, thanks to Captain Cubitt's kind and painstaking co-operation. It may be well to know that there was one special problem to be solved which dominated all others : could we find the proper position, and, having found it; could we keep it Figs. 149-151 PLATE XLIV, No. 1.--11 h. 49 m. 20's G.M.T. No. 2.--12 h. 3 m. G.M.T. No. 3.--12 h. 11 m. The Eclipse of the Sun, April 17, 1915, as seen at Bournemouth. (Notice that 2 and 3 represent crescents of the Sun of the same form, but a different part of the Sun is exposed to view.) 136 A series of three images showing different phases of a solar eclipse. A crescent-shaped image of the Sun during the eclipse. A crescent-shaped image of the Sun during the eclipse. PLATE XLV. Fig. 152-153 cell stage cell stage Total Eclipse of the Moon, Jan. 28, 1888. [1364] Figs. 154-155 PLATE XLVI. 3rd stage. 4th stage. Total Eclipse of the Moon, Jan. 28, 1888. A black and white photograph showing two stages of a lunar eclipse. The top image shows the moon with a crescent shape, and the bottom image shows the moon with a more pronounced darkened area. 1360 Figs. 136 PLATE XLVII. Total Eclipse of the Moon, Jan. 28, 1888. Occultation of Jupiter by the Moon, Aug. 12, 1892 (W. H. Pickering). 137 SKETCHING THE CORONA. 737 for two hours, and especially for the 10 minutes which would include the critical events of the eclipse; and would the ship be steady enough on the water to enable the necessary observations to be made? Everything happened just as was wanted, A diagram showing concentric circles with lines radiating outward from the center. The lines appear to represent the path of a celestial body, possibly the sun, moving across the sky. The circles are labeled with time intervals, suggesting that this is a diagram of a solar eclipse. Fig. 161.—The Corona, Aug. 8, 1896, as sketched by E. J. Stone's system. the most remarkable thing of all being the steadiness and the fixity of the ship. This last was accomplished by the ship being kept moving at the calculated speed of three knots an hour, which neutralized the strong set of the current in the reverse direction. All of us, or most of us, were able to 138 ECLIPSES. observe the usual concomitants of total eclipses of the Sun ; but only the feature needing notice here was the lack of darkness of the sky during the interval of eclipse. Probably that was the result of our viewing the eclipse with nothing but water surrounding our place of observation. Fig. 1 represents the diagram devised by E. J. Stone for noting down in haste the streamers, etc., visible in a total Eclipse of the Sun. The diagram is an instance of its actual use by Stone on the occasion of the Total Eclipse of the Sun of July 29, 1878. The lines drawn to represent the rays employed for other purposes if copies of it, printed on cards, are kept for use with a telescope. In case of oscillations of the Sun's disc, which may occur at intervals of several hours, stars will disappear and reappear, may be marked before- hand ; and so time may be saved, and the stages of the phenomenon not lost because the observer is not sure where the Sun is situated. Other uses of this card can be made ; themselves to an observer from time to time ; for instance, in observing the Sun or double stars they will come in very handy. We will now consider the eclipses of the Moon in some further detail. It may be said, generally, that whilst, for reasons mentioned in an earlier part of this chapter, these eclipses are more often visible to those who choose to look for them than eclipses of the Sun, yet they are less frequently seen. The eclipses of the Sun, partly for the reason, no doubt, that they are devoid of sensational features of display and points of general interest. Indeed, almost the only matter which attracts attention is whether or not they are worth to put down on his agenda is the question, What will be the aspect of the Moon when most deeply immersed in the Earth's shadow ? Will it be " all or all" or will it be invisible ? If visible, how will it look ? Of course one may say that, by right, it ought to be altogether invisible, and so very frequently it is ; A diagram showing a total solar eclipse. Fig. 165 PLATE XLVIII TOTAL ECLIPSE OF THE MOON. (Tempi) 1867. A circular illustration showing a partial eclipse of the moon. The moon appears reddish-brown during the eclipse, with stars visible in the background. [API_EMPTY_RESPONSE] ECLIPSES OF THE MOON. 139 but, on the other hand, it is frequently visible between the extremes of showing traces of its existence, and showing its entire disc, according to the variable condition of the atmosphere. There are no discoverable laws which regulate these variations, and it can only be said, very vaguely, that they depend upon the variable condition of the Earth's atmosphere. It has been observed by several observers, that the Sun's rays have to pass are highly saturated with aqueous vapour, the red rays will be transmitted freely, and the Moon's disc will appear white; but when the other rays are absorbed, as also the blue will predominate, the illumination will be extinguished. In the case of a total or partial eclipse, some parts of the Moon's disc are visible and others invisible, the variation may be considered due to the prevalence of moisture in some places and its absence in others; this is a very general remark, and its absence in other parts, thus emphasising the dis- tinctions just pointed out. It is right to add that, by various competent authorities, the foregoing explanations are deemed insufficient; but I think better time yet being lost in substitution. There have been many records of eclipses of the Moon recorded which have been of great part in certain maritime events. An experience which befell Christopher Columbus is a case in point. In February 1504 Columbus found himself at the Island of Jamaica; he was then about to set sail for Spain, but the slanders refused to provide, and he was therefore at his wit' end to know what to do. What followed shall now be told in the words of his son --- **Hebethoughthimselfthat,** within three days, there would be a lunar eclipse in the first part of the night; and then sends an Indian of Hispaniola with us to call the principal Indians of that province, saying he would talk with them about a matter of concern. Being come that day before the eclipse was, A diagram showing different types of lunar eclipses. 145 ECLIPSES. he ordered the interpreter to tell them that we were Christians and believed in God, who sent us down and took care of the good and punished the wicked ; . . . that, as for the Indians, seeing how neglectful they were in bringing provisions for our coming, he would punish them with plague and famine ; which because, perhaps, they did not understand what was meant by these words, he gave manifest tokens of it in the heaven, that they might plainly know the punishment was to come from Him. Therefore he told them that if they would not bring us provisions, they should see her rise angry and of a bloody hue, to denote the punishment of their neglect ; and that if they would do this to them, the Indians went away, some afraid and others looking upon it as an idle story ; but the eclipse, beginning as it did, made them tremble and fear. And when the Indians took notice of it, and were so frightened that they came running to the Admiral, he gave them a great deal of lamenting, and prayed the admiral by all means to intercede with God for them, that He might not make men feel the consequences of their neglect. The Admiral said he would bring him all he wanted. The admiral said he would speak to them again tomorrow morning ; and then he went out crying still out of him to assist them ; and when the admiral saw the eclipse began to go off, and the Moon would soon shine again, he said that God had heard his prayers ; He was God for them, and promised Him in their names they would be granted their request ; and that therefore they must bring provisions and other necessaries ; and that therefore God forgave them, and as a token of it they should see the anguish of their enemies ; and that if they would not bring them provisions just as he spoke it, they gave the admiral many thanks, and praised God for His goodness to them. From that time forward they always took care to provide all that was necessary, ever praising the God of the Christians ; for they saw that He had given them a sign which showed them denoted mischiefes to betray them ; and being ignorant of the cause thereof, they thought it was a sign from God. And believing it possible to know on earth what was to happen in the heavens, they certainly concluded the God of the Christians had revealed it to them. See Inckerton, Pignes, vol. xii. p. 187. EXTERNAL CONTACT 1 SUN 11 INTERNAL CONTACT 111 Fig. 103.--Phases of the Transit of an Inferior Planet. 145 142 ECLIPSES. This story records alike the credulity of the natives and the mingled piety and autumness of the great navigator. It might well be regarded as an example of that worst of all frauds, a "pious fraud." The most recent instance of the utilisation of a total eclipse of the Moon occurred on December 16, 1893. What happened is thus described by the Times correspondent with Lord Melville's army at the Modder River in South Africa: "The Full Moon has prevented satisfactory search-light communication between the two armies, but we are expressly of the eclipse last night to get important despatches through." Akin to eclipses of the Sun are two astronomical phenomena which go by the names of "Transits" and "Occultations." They are entirely identical in principle with solar eclipses, but involve other celestial bodies. In 1750 it was pointed out that the two Inferior Planets, Mercury and Venus, are constantly passing round the Sun, and between the Earth and the Sun; and that whatever may happen to any one of them, it will always pass behind the planet, whichever it be, will be seen projected on the Sun's disc. On such occasions (which are very often in the case of Mercury) a dark spot appears on the disc of the planet, and then the appearance of a sharply defined round black spot. The occurrence of such a transit offers an opportunity for determining the distance of the Earth from the Sun. This has been done with great success for Mercury, because of its proximity to the Sun; but Venus has frequently been used for obtaining a solution of this problem. The transit of Venus across the face of the Sun takes place only once in about 7 years, and beyond the scope of this volume. Suffice it, then, to say that it depends for its success on the skill and care with which observers at remote distances from one another on the Earth OCCULTATIONS. 143 can determine micrometrically the exact points on the Sun, as viewed from northern and southern stations on the Earth, at which the planet appears to enter and to quit the Sun's disc in the course of its passage across the Sun. By the application of trigonometry (or by means of tables of angles) the distance desired to be known can be calculated. The satellites of Jupiter also perform transits over their primary's disc. The duration of which, (based on the important fact that they are always seen in the same part of the sky), furnishes interesting data for a study of the planet's standpoint. They also suffer eclipse by passing behind the planet. Both these Jovian phenomena are dealt with in the next chapter. An Occultation, in the literal meaning of the word, is the covering over of one celestial body by another. Accordingly, when a star passes behind the Sun, we say that the star is occulted by the Sun; but the word "Occultation" is by usage confined to cases where the Moon hides a planet or a star, or one planet hides another planet or a star. Occulta- tions are rare events, because the heavens are common enough and occur daily. Sometimes the Moon occults a planet, which naturally intensifies the interest in such occurrences. In this case, however, only those stars brighter than the 6th mag. anticipations of the occurrence will be found stated in the Nautical Almanac whence the information is copied into Whittaker's Almanac and other similar works. But even when a planet is occulted by a New Moon and First Quarter the effect is very striking, because the star occulted is suddenly extinguished at a point where the observer sees it most distinctly. This is therefore an excellent reason for anything to interfere suddenly with the Star. Occul- tations may be said to be celestial phenomena specially within the province of amateur observers, when they take place with the Moon young or old, they happen at conveniently early hours in the evening, and are within the reach of telescope however small. CHAPTER IX. COMETS. Always objects of popular interest.—Very numerous.—Telescopic comets. Great comets visible to the naked eye.—Changes in the appearance of a comet.—The tail of a comet.—The nebula.—Usual changes exhibited by a telescopic comet.—Become visible only when the sun is near the horizon.—The tail of a comet—does it come from ?—Why do some comets have tails and not others ?—Types of comets.—General account of tails.—Some tails probably cylindrical.—Bra- dley's theory of the origin of comets.—Periodical comets.—Celebrated comets.—Some statistics. It may safely be said that the remarkable objects to be dealt with in the present chapter had a good deal to do with the remarkable progress of astronomy, assisted by the increased space devoted to it by the press, and by the liberal subventions granted in the United States, especially during the last 30 years, by wealthy men through the establishment and endowment of astronomical observatories. I name the period of 30 years because that takes us back to the year 1857, which was a very important year in astrono- mical history, much more I think than did the "great comets" of 1818 and 1861, which were in all respects finer objects than the comet of 1881. All these will require notice further on. For this reason I must first give a general account of the details, the true understanding of which is essential if we would get a clear and satisfactory grip of this branch of astronomy. 44 CLASSIFICATION OF COMETS. 145 Comets may be said generally to range themselves in two classes: very small ones, seldom if ever visible to the naked eye; and those which, though they may be seen with the naked eye, exhibit tails of considerable length, which may be between two or three diameters of the Moon and half the extent of the visible sky. The former class will be considered first. Fig. 164-165.—Brooks's Comet of 1898. (X.) degrees long may be said to present itself every two or three or half a dozen years. Here we have to face, at the outset, a popular view of things which altogether fails to accommodate itself to the superior knowledge of the professed astronomer. Ask the first person you meet on this subject what is a comet?—and the answer will always be something like this: "A celestial object which Two images of comets. The left one shows a comet with a long tail extending across the sky, while the right one shows a comet with a shorter tail. Both comets appear to be moving away from the observer. 146 COMETS. appears unexpectedly and has a tail." Such an explanation and such a limited definition totally fail to represent the facts of the case. It brought home forcibly that we can see with a duly equipped telescope. He would tell us that, in the course of two or three years, he had seen probably at least half a dozen comets, and that they all had tails. But this was only because he possessed a tail. In point of fact, it may be stated broadly that, in the course of a generation, dozens of comets come within our reach, most of them very diminutive in size and brightness, and none of them have any visible tail. The astronomical parlance as "telescopical comets," though it occasion- ally happens that here and there one, some weeks or months after its appearance, shows a tail, is not applicable to those which greatly in size, puts forth a tail, and becomes to the man in the street alone worthy of the title of "comet." Dunlop's comet (1857) is known as the "great comet" of that year, but the one within my own personal recollection which is the most striking manner best illustrates what I have just said. Discovered by Donati at Florence on June 10th, 1858, it was visible to the naked eye until that year. On one evening in the first week in September I could just manage to see it in a portable 3-inch telescope. It then became so brilliant that I could see it distinctly through the eyepiece of my 10-inch refractor. It was one of the largest and most magnificent comets on record, not quite so much from the length of its tail (though that extended to about 60°) as from the wide, fan-like expanse of the tail, and its great brilliancy. I have cited Donati's Comet as illustrative, albeit in an extreme degree, of the changes which telescopic comets often undergo. They are not always so conspicuous as this one; indeed, more humble position in the ken of the astronomer. Whether such an object is found as the result of systematic search for comets or is picked up by chance in a telescope about to be used for other purposes, it is glimpsed, present in appearance of a tiny imo, cloudy patch which may C.MET HUNTING. 147 or may not have a sharp, star-like centre. Even when found and presenting such an aspect, the fact of its being truly a comet cannot at first sight be known for a certainty, for there are many comets which appear to be stars, and which are seen at first sight, and indeed often have been, regarded as comets, and been publicly announced as such. The discreet astronomer will not be misled by this confusion does not rush at once to the nearest telegraph office or newspaper office and announce his discovery of a comet. He will wait for a few hours to see whether the object which he has seen is stationary or in motion with respect to the stars. It generally happens that three or four hours will enable him to decide whether it is one way or the other, but it frequently occurs that the observer sees a shower of clouds shut out the object under scrutiny, and he must then resort to the observatory for its motion, if any, to be ascertained, and the observer who thinks and hopes he has found a new comet must wait until the following night before he can safely announce his success. What I may call an ordinary telescopic comet usually passes through the following stages of development : when first found it is a mere luminous patch, or is near the centre of which a slight concentration of light either is seen at the very first, or Fig. 168.—Diagram to illustrate the Recognition of a Comet as distin- guished from a Nebula. 148 COMETS. after an interval develops. This, when it acquires something like a distinct central brightness, becomes known as the "nucleus." The nucleus may increase in size and beauty until it increases, supposing that the comet is approaching both the Earth and the Sun: the hazy, nebulous matter around the nucleus becomes broader and brighter, and is then spoken of as the "coma." When this coma has reached its maximum, very likely the coma will go on expanding in one direction, and, after giving the whole object an elongated or oval shape, it will gradually become more and more immersed in the twilight until it is lost in the rays of the setting Sun. After an interval it will again appear in the evening twilight, on the other side of the Sun in the morning twilight, and gradually recede from the Sun until it becomes lost either in broad daylight or at night. In this way, by day and by night, under ground, it will be lost to view owing to its continuous diminution of apparent size due to its increasing distance from the Sun and the Earth. The foregoing account of what may be called the rise and fall of a comet, so far as its career from a terrestrial point of view is concerned, will suffice to convey a general notion of what happens to these bodies; but, of course, particular comets, by reason of their notorious vagaries in the heavens, TELESCOPIC COMETS. 149 may come and go without conforming to the stages of history set forth above. For instance, it often happens that a comet is seen for the first time, and then disappears, so far as we are concerned, is coming to an end by reason of the fact that its nearest approach to the Earth and to the Sun happened some years ago. It may happen that a comet which was first seen it was well on its way on its return journey to the unknown realms from which it came. Fig. 167.—Telescopic Comet without a Nucleus. Fig. 168.—Telescopic Comet with a Nucleus. The subject of cometary astronomy is such a very large one that it is not easy to know where to draw the line as regards going into details. The changes which the small telescopic comets undergo during their passage through our solar system are beyond the scope of considerable power, and it is doubtful whether these changes appeal to the general reader or popular student. It is fair to say that with the aid of modern instruments varieties of tail and the changes which have been noted in the tails of particular comets open up a large field both for 130 COMETS. descriptive writing and for speculation. It must suffice, how- ever, here to state a few general outlines. Three questions frequently asked are: "What is a comet's tail made of? " Where does it come from? " and "Why do some comets have tails and others not?" It is impossible to give satisfactory answers can be given to any one of these three questions. The first, especially, is an inscrutable one, and a remark made by Sir William Herschel, in 1786, when he was young, a century ago, may be cited as an indirect indication of the uncertainties which confront us. He said, in a famous passage, that the tails of comets probably, as a rule, only reflect a very feeble light. This is true enough; but it is not so much the light but it is hard to disprove it, and it is equally difficult to prove it, and a contented confession of agnosticism is perhaps the safest attitude to adopt. The second question, "Where does the tail of a comet come from?" is a little more easy to deal with, because we have some certainty about its origin. The tail of a comet is always in con- nection. Whilst in a certain number of cases it may be said, with Topsy, that the tails simply "grow" by visible expansion from the comet, yet there are not a few well-established cases in which the tail has been seen to issue from the head. The central head of a comet precisely as a jet of water may be seen to be thrown up from the mouth of a fountain. The third comet of 1858 was observed to emit jets from its head. This is a remarkable instance of what may be called the jet origin of a comet's tail; but there are many other instances on record. The natural idea which the observation of a comet developing a tail suggests is that the tail consists of radiant, luminous matter which is thrown up in the fashion of an Iceland geyser. This is how the matter may be said to come out of the head. But this view cannot be maintained when we realise how such a vast mass of luminous matter can be pro- duced in or from the head of a comet, bearing in mind the For. 169-170 PLATE XLIX. A black and white photograph of a celestial body, possibly a planet or moon, with a bright central area and a darker outer ring. The image is labeled "Jum. 13. - Brook's Comet of 1854" (L. T. Thackeray). The label also indicates the direction of the tail. 130] Fig. 171 PLATE I. Encke's Comet, Sept. 22, 1848. (As seen at the Hartwell Observatory.) 134 THE TAILS OF COMETS. 151 evidence we possess of the ethereal character of these bodies, and their lack of solid substance and weight. On this question of lack of mass it may be necessary, and more convenient, to say something later on. The question as to why some comets have tails and not others, has been discussed by many astronomers, but no satisfactory astronomy which is incisurable. Speaking generally, it may be said that very small comets have no tails, and that very large comets always have tails. This, however, brings us no nearer to the solution of the problem. It is only possible to assert that very small comets which are no brighter than the stars of the tenth magnitude or smaller (and there are such), never have tails. The larger comets, those which are very large and compact comet visible to the naked eye and without a tail is unknown. It is true that one or two comets are on record as having tails and large ones. Full Moon, but our knowledge of these depends upon ancient records wherein habitual silence of language and lack of precision seriously discount their testimony. It is impossible here to describe in some detail certain of the features which have been recorded in the case of comets seen in the past. In the first place, when a comet has a tail, it is usually seen to be moving away from the Sun; that is to say, it has shot forth in a direction behind the comet rather than in front of it or towards the Sun. This is no more than the common case of the tail of anything, whether it be a ship or a kite or a balloon. There are a few instances on record of comets having had not only a normal tail, properly so called, but a short stubby tail, which was described as "a beard" by Sir William Herschel. Such a tail is usually spoken of by old writers as a "beard," and the sense of the expression will be obvious from what has just been said as regards tails generally. The fact of tails of comets being usually turned away from the Sun was noted on an interval between 1780 and 1781. 153; but 152 COMETS. the Chinese seem to have noticed the same fact 700 years previously. When a comet has a tail, in the majority of cases there is only one such appendage, but two tails are not uncommon, and there have been cases of three, four, and five tails, whilst the celebrated comet of 1861 had seven distinct tails. It is important to note that it sometimes happens that, though a comet can only be fairly described as having one tail, yet now and then it will be found to have several tails, each emanating from the same centre as the main tail, and these streaks ought rightly to be numbered as distinct tails. This attribute of subsidiary streamers in the nature of tails was observed by many ancient astronomers, and others describing comets which they had studied ; but the application of photography to cometary observations has in recent years in several instances shown that this phenomenon must really be spoken of as a multiplicity of tails. Photographic graphs undoubtedly a wide range of details than does human vision. Under ordinary circumstances, while a common type of comet has a common type of simple tail, there is nothing in general to catch the eye and lead one to any precise conception of its nature. But when we come upon a comet with more perfectly developed tails, one sees the two edges distinctly brighter than the centre, and this compels the conclusion that the whole body of the comet is conical in shape. That a tail is of this formation is obviously suggested by the fact that, if we look at any luminous cylinder sideways, even if really illuminated evenly all round, it will in projections look like a cone. This is because we see only the edge of the viewing the edges through a concentrated thickness of material, whereas the portion of the cylinder midway between the illuminated edges is not seen at all. It is easy to see how this may be said to speak. This may be tested in several obvious ways in connection with domestic illumination in our houses, and CLASSIFICATION OF TAILS. 153 assuredly gives us a clue to the true form of many conetary tails. Where a comet has evidently two distinct tails (not the appearance of two tails in virtue of the explanation just given) it almost always happens that the two tails are of different length, and that the shorter one is inferior in brilliancy to the longer. Except in the case of small comets with short tails, it is seldom that a tail is straight; it is most usual for the tail to DER STERN DROHNT BOESE SACHEN TRAV MR GOTT WIRD SVVOL MACHEN. Fig. 172.—Medal distributed by the Monks to avert Misfortune during the Appearance of the Great Comet of 1680. be curved, and the curvature is the natural result of the comet's head being more luminous than its body. The Monks keep pace with it because of its much dimmer material. This, at least, seems a fair and proper way of condoning the condition of things. The astronomers of the present day, working on different lines, have endeavoured to classify the tails of comets on the supposition that there is an individuality about tails, which shows that they are not all formed in the same way or under similar conditions. The most systematic of these classifications 154 COMETS. is due to the Russian astronomer Bredinich, who has worked at the matter with great zeal and moderation and discretion of language and conclusion, and stress on this description of his labours because there has been of late years a great dissonance on the part of astronomers of a certain sort to put forth proofs for the existence of comets, which have been made up of the tails of comets, with a very limited amount of proof available to support their views. Bredinich's investigations led him to consider comets into three classes: (1) long straight tails (q.) and no plume-like tails; (2) short, stubby, and sharply curved brushes of light. Bredinich's First Type of tails he considers matter of ordinary appearance, but the second type of tails act with an activity very much greater than the Sun's attractive action in virtue of the general principles of Gravitation, so that the particles of cometary matter are continually being drawn towards the Sun with a relative velocity which rapidly increases and eventually becomes enormous. The long, straight streamers, which I have already alluded to, were well exemplified in Bond's drawing, "The Comet," where they are represented as being composed, according to Bredinich, of hydrogen gas. The Second type of tail is by far the most usual one. Here the reverse process takes place; the particles are repelled from the comet may be said to be more completely and continuously under the attractive control of the Sun. Some kind of hydro- carbon gas is believed to be the constituent of tails of this class. The Third Type of Tail is that which is capable of much expansion of size, are thought not to be subject to any great amount of repulsive influence, but to be dominated for some time by an attractive force. This is a matter of which they are composed is thought to be in a state indicative of far greater heaviness than obtains in either of the two previous classes, and to consist of the vapour of iron, perhaps also of sodium, and other substances. It is quite evident that these points are of a very speculative character; Fig. 173 PLATE LI Halley's Comet, Naked-eye View in Mexico (L. G. Leon). 254 Fig. 174 PLATE LII. Curious Aspect of the Head of Halley's Comet, June 8, 1910. (L. G. Leon.) 155 CLASSIFICATION OF TAILS. 155 but still Bredinich's ideas cannot be condemned as destitute of possibility and probability. The American astronomer, Professor W. H. Pickering, of Harvard College Observatory, divides the tails of comets into two classes, and sets up a distinction on lines entirely different from those of Bredinich. He seems to con- sider that the tail of a comet may be divided into two cases, may be, a tail which we should at the first glance regard as a simple tail, really, when carefully looked into, may comprise two parts, one of which is the head of the comet itself, the other in the cone's head, surrounding and enveloping which there is another tail (which perhaps rather should be called an en- velope) which is formed by the rays of light reflected from the cone's surface. This view is supported by Mr. L. C. Searle, who says that, "judged by the photographs of recent comets, the former kind is much the more common of the two, and consists usually of a bunch of rays, more or less in bright, pro- nounced order." Mr. Pickering himself has given an account of his views in his "Catalogue of Comets," published in 1876. He thinks that his second type of tail is well represented in the pictures in existence of the "great comet of 1811," of the "great comet of 1835," and of the "great comet of 1843." He considers that Swift's comet, of 1823 (i.), was an instance of both types of tail being present at the same time, and that Swift's comet had its first perihelion passage before its tail of a different type after its perihelion passage from what it had before the perihelion passage; that at the earlier period the tail had its origin in the nucleus, but that at the later period the tail was formed by rays issuing from the nucleus and wrapping up the head, but distinct from it. Pickering goes on to suggest that the enveloping type of tail is much smoother and more regular than the rayed type; and he adds that it is that is the kind which seems to have been present in at least three of the five great comets of the 19th century, namely, those of 1811, 1835, and 1843. The foregoing qualifications, however we may regard them, do not directly help us in coming to a conclusion as to the 15 COMETS. originating cause of a tail where a comet, when discovered, is tailless, and afterwards becomes furnished with a tail. As to this the theory generally favoured by astronomers nowadays is that what is called "light pressure" is concerned in the creation of cometary tails, probably under impulses which cannot be measured by any known instrument, but which have a character. "Light pressure," as a phrase standing by itself, may conveniently be defined as being based on the supposition that all bodies emit light, and that the cumulative push on all materials on which the light impinges, whatever its source of the light or the nature of the material. Thus far the attention of the reader has only been called to few facts, and to the fact that the first light upon naked-eye observations of any casual comet which might appear; but much more must be said if we would obtain a proper conception of the subject. The number and the number of the comets and of their paths through space opens up a variety of topics which, though in a certain sense subsidiary to what has gone before, are of the greatest intrinsic interest. In olden times it was not considered that comets, as regards their movements, were subject to any laws, but then they came with great regularity at intervals of about three years until quite modern times that it was realised that they were subject, to a certain extent, to the same laws of motion as those applied to other bodies in the solar system. This is true; whilst it is true that a large number of comets come to us from whence we know not, and then pass away whilst we know not, yet there are a certain, not incon siderable, number which return again after some interval. They enter the solar system, and come and go, and after a certain interval come back again. These are termed "periodical comets," and bear a close resemblance in their motions to other movements, the principal point of difference being that, whereas the planets all move in orbits not materially differing from Fig. 173 PLATE LIII The Great Comet of 1811. PLATE LIV. Fig. 176 The Comet Coma of 1843, March 17. [137] PERIODICAL COMETS. 157 circles, not a single comet moves in an orbit which is anything like a circle. The orbits of the periodic comets are all of the same kind, and their motions are so regular that they can be understood by saying that all the periodic comets move in oval orbits, which may be compared roughly to flattened circles. The reason why the orbits of comets are only such eccentricity, but also in their dimensions. Thus it comes about that Encke's comet, with its period of only a little more than three years, performs its journey round the Sun in an orbit which is nearly circular, but with a semi-axis of 300 million so far away from the Sun in the course of its voyage of 75 years that when at its greatest distance it is quite outside the solar system, because it attains a point outside the orbit of Neptune, and therefore does not pass planets. The comets which are not periodic do not move in any fixed path; so far as we know, come to us in paths which the mathematician calls "parabolas" and "hyperbolas," though the number of the comets which have been known for a certainty to have pursued hyperbolic orbits Going back to the periodic comets—whilst the known or supposed periods vary between a handful of years and thou- sands of years—there are three classes : (1) Comets with periods between 3 and 15 years. (2) Comets with periods averaging 70 years. (3) Comets with periods of many hundreds of years. Of these three classes, two belong to the first class ; and 2 can it be positively asserted that they are permanent members of the solar system. This is certain, because they have proved their permanence by having made several visits; indeed several of them have paid several visits. Our knowl- edge of the comets in the third class is much less certain, for the reason that, owing to the length of their periods, no oppor- tunity has yet occurred for them to pay a return visit. There is indeed no comet whose period which astronomers since 158 COMETS. hoped might safely be regarded as a permanent member of the system; but the supposed orbit broke forth. There appeared in 1550 a brilliant comet which was thought at one time to be a second appearance of the great comet of 1264, one of the grandest on record. Its return about 1860 was confidently reckoned upon by astronomers, but it did not appear. There have been other comets observed during recent years, which, it has been calculated, move in elliptic orbits, and must therefore be regarded as temporary members of the system. But, in the period of some of these amount to thousands of years, it is evident, not only that the world will have to wait for a very long time before seeing them, but also that doubt attaches to the exact character of their orbits. In many instances they are the same, to say nothing, in some instances, of the lack of a sufficient number of trustworthy observations when they were within sight. The following are the names of the short-period comets which may be regarded as well-recognized members of the solar system:
No. Name. Period in years. Next return
1. Eckels' Comet (1873 ill.) 3.90 1914
2. Templ's Second (1873 ill.) 5.55 1914
3. Templ-Swift's Comet (1873 v.) 5.53 1914
4. Wright's Comet (1873 v.) 5.59 1912
5. Bresen's Comet (1873 v.) 5.59 1912
6. Fur's Comet (1873 v.) 6.64 1917
7. D'Arrest's Comet (1873 v.) 6.64 1917
8. Nichols' Comet (1873 v.) 6.85 1913
9. Holmes' Comet (1873 v.) 6.85 1913
10. Borely's Comet (1873 v.) 7.07 1913
11. Herschel's Second (1886 v.) 7.07 1920
12. Paye's Comet (1886 v.) 7.44 1915
13. Tuttle's Comet (1892 v.) 7.460 1934
A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years, and next returns. A table listing comets with their names, periods in years,139 Figs. 178-183 PLATE LVII June 16. June 18. June 20. July 1. July 6. The Comet of 1860. (III.) (Cannellotti, p. 459.) July 7. FAMILIES OF COMETS. 159 With reference to two or three of the comets in the fore-going list, the date of whose next return is suggested, it is A diagram showing the orbits of comets around the Sun. The orbits are labeled with their respective dates of perihelion passage. Fig. 184.—The Comet Families of Saturn, Uranus, and Neptune (Drawn by H. C. Wilson). to be understood that, though they have made several returns in the past, they have not been seen very recently, and in some degree a mystery hangs over them, their orbits appearing to 160 COMETS. have been deranged by the influence of the planet Jupiter. The whole group of 13 consists of small comets not as a rule visible to the naked eye, though some of them are some times so visible when favourably placed with respect to the Earth. All the comets in the list on p. 158, except Tuttle's, are to be regarded as members of what is called the "Jupiter family of comets," and some other comets whose orbits are not at present known to us may also belong to this group at a future time. It is considered now that all the members of the planets beyond Jupiter, namely, Saturn, Uranus, and Neptune, have their comets associated with them. The long-period comet which is best recognised as being those which it is safe to regard as members of the solar system, though not all of them have been seen twice, are the following:
No. Name. Period in years. Next return.
1. Westphal's (1852, iv.) 60 (?) 1913
2. Foucault's (1857, vi.) 70 (?) 1955
3. Dí Vico's (1846, ii.) 72-75 1900
4. Oberst's (1834) 74-5 1960
5. Bourget's (1842-v.) 74-5 1960
6. Halley's (1682) 76-79 1986
The only one of these six comets which calls for any special mention is the last-named, Halley's; but the story of Halley's comet is now so well known that it would be tedious to give it at any length. Sir Isaac Newton and Edmund Halley share between them the honour of the comet which now bears the name of the latter, and even in a skeleton form its story is very interesting. Sir Isaac Newton gave to the world in 1681 his celebrated HALLEY'S COMET. 161 treatise on Universal Gravitation which is best known by the simple name Principia, but of which the full title is Philosop- hiae Naturalis Principia Mathematica. The first edition of this book appears to have been borne by Halley, and, after studying his venture, the idea came into his head to try and see whether Newton's labours could be utilised for obtaining information about comets. This was done with great success by Halley himself in 1683, though not discovered by him, seemed to offer the desired opportunity, and he calculated its motions with great accuracy. In 1705 he published a work after finishing his calculations with regard to the comet of 1685; he turned his attention to the recorded observations of comets which had appeared in 1660 and 1531. The results of these investigations were so satisfactory that many of all particulars that he did not long hesitate in coming to the conclusion that the three comets were really one comet, and that it would return again about 1758. He was thus confirmed in his system. He had sufficient confidence in his own work to venture on the prediction that the comet would return again about 1758; and this prediction was confirmed by the appearance of the Comet of that year by a Saxon farmer named Pallasch, near Dresden, and of the calculations made in anticipation of its return, is a thirteenth-tale told. Halley died in 1742, and left behind him a large number of papers on mathematical subjects; posterity will not refuse to acknowledge that this [periodicity] was first discovered by an Englishman. The discovery of these parts of Space in 1833, and the whole subject of mathematics as applied to orbits had made such progress between 1758 and 1833 that the comet's periodicity, as it has been estimated, was found to be wrong only to the extent of about 4 days. The last return of Halley's Comet at perihelion in the spring of 1910 will be fresh in the minds of all my readers--how it was for the inhabitants of the northern hemisphere, a great disap- pointment, whilst dwellers on the opposite side of the world A page from a historical text discussing Halley's Comet. 162 COMETS. enjoyed a magnificent sight. The pictures annexed will give its appearance at various times when seen in various places. In England it showed itself as quite an ordinary comet, just visible to the naked eye, and not very conveniently placed, being near the Sun in the evening twilight. But, after its peri- helion passage, it was seen in the morning sky, on the other side of the Sun, and was visible in the early morning, those who had that opportunity by reason of their being in Africa, saw it as a very brilliant object, and a magni- ficent object with a tail extending half over the celestial sphere. The world-wide interest felt in Halley's Comet in 1910 is well shown by the following account of it which came from the far-off South Seas: "On May 9 the comet, looking like a muffled star, was seen in the East, and its tail, a broad beam of brilliant light, ex- tended upwards towards about 3°." Below the comet and a little to its right was a bright star. "It was seen look- ing far bigger than any planet I have ever seen." The comet extended across the heavens for about 5°. "At this time that we saw it completely before it had passed the Earth," the tail blazed across the heavens like an immense searchlight; but soon after it began to fade away, and again in the evening reduced in size to about 4°; and several more nights later it was only seen as a faint star, from our sight. Superlative expressions will not describe Halley's Comet as we saw it in New Guinea; it was a wonder- ful sight. It was seen by all who looked for it, and the Javanese declared that it portended much sickness and death among them. "We do not know why," we never learnt how it impressed the minds of the natives." A matter which caused much discussion, both as a matter of prophecy and fulfilment (or non-fulfilment), was whether the comet had crossed the Sun as seen from the Earth, and whether it had been destroyed within doing so. The conclusions were that it had made mistakes. WOLLASTON, Pigmies and Papuans. Fio. 185 PLATE LVII. A photograph of Halley's Comet, May 1, 1910. The comet is visible as a bright, elongated object against a dark starry background. Halley's Comet, May 1, 1910. Photographed at the Transvaal Observatory. 160] Figs. 186-191 PLATE LVIII. May 5, 5:45-5:45 p.m. C.T.S. May 5, 5:40-5:35 p.m. C.T.S. May 5, 6:00-6:15 p.m. C.T.S. May 5, 6:07-6:35 p.m. C.T.S. May 30, 9:00-9:30 p.m. C.T.S. June 3, 9:00-9:30 p.m. C.T.S. Halley's Comet, 1910 (D. H. Morehouse) [163] HALLEY'S COMET IN 1910. 163 arrived at were indeterminate: it is probable that the comet did cross the Sun's disc, and ought to have been seen, but it was not observed. On the other hand, it appears quite certain that the Earth passed through a very thick part of the comet's tail, though nothing inconvenient happened. It may be stated, by the way, that the question of a collision PATH OF HALLEY'S COMET
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The ancient Greeks believed that comets had the slightest justification for alarm. It is quite certain that in 1801 the Earth passed through a very thick part of the tail of the great comet of that year, but nothing happened beyond a sensation of fogginess which impaired the light of the Sun, 164 COMETS. shining at the time, and led in one case, at least, to a demand for artificial light at the early hour of 7 p.m. on June 30, when it was noted that the sky was covered with a glassy, white shining, but not as usual. To give a list of all the comets which might be included the adjective "great" would be still more to describe them, would run into many pages. Let it suffice, then, to mention the following, belonging to the 19th century: 1811, 1825, 1842, 1838, 1851, 1874, 1883, and 1882. This far in the 20th century we have had only Halley's (1605), and one or two which can only be described as second-class. A black and white illustration of a comet with a long tail. The comet is labeled "HALLEY'S COMET" and "SPECTROSCOPIC PICTURES." The illustration is credited to "WALTER WARNER MEDAL" and "NEW YORK UNIVERSITY." The comet is shown in various stages of its orbit around the sun. Fig. 193.—The Warner Prize Medal. comets, as to other celestial objects. The general result is to show that cometary spectra, more often than not, belong to one type only, that of the hydric-carbons. Up to the present time historians and astronomers together have recorded a total of about 1000 comets. Of course, even up to the year considered, comets noted were naked-eyed ones ; but, seeing how nowadays the naked-eye comets fall short in number of the telescopic comets, it is safe to assert that during the Christian era, several thousand comets have visited our system. In case a reader may be surprised at the number of comets 76.18 A black-and-white illustration showing a celestial event, possibly a comet or a meteor shower, with several streaks of light crossing the sky. The left side of the image has a handwritten note "Jan 2. 1744. 300000." and "Comet." The right side has a handwritten note "Col. Warren" and "The Fall of the Great Comet of 1744." According to contemporary tech." **FIG. 154.** The Fall of the Great Comet of 1744. 165 166 COMETS. discovered in America of late years having been so large com- pared with the number discovered in all other parts of the world, it must be seen while we consider the great value which prizes in money and medals are systematically awarded to those who are able to prove priority in picking up new comets. The Warner gold medal was given to the discoverer of the comet which American astronomers have before them to encourage their valuable work on behalf of science. This chapter may be usefully concluded by some brief notes in detail on the comets which have been selected to illustrate it. THE GREAT COMET OF 1741. This comet historically was long a mystery, for the statement that it had 6 tails, announced in books all over the world, was very soon shown to be false. It was only after a careful exam- plored testimony of one man. But some years ago, in a curious way, there came out evidence of a contemporary writer that the comet had really possessed a number of separate tails ; and the writer says that he saw six tails at one time, but that they were considerably more than six tails. The number of six seems to have been arrived at by counting the streamers in pairs, each pair comprising the two sides of one tail properly so-called. THE GREAT COMET OF 1843 (5). This comet appeared with great suddenness, and was ended with peculiarly rapid motion, and had a tail fully 100' long. It would seem to have been one of the grandest comets on record, when we consider that no less than three men in Europe had seen the great comet of 1811 as well, and on the other hand those who had not seen 1811 but had seen Donati's Comet of 1843, I consider that one is justified in saying that the 1843 comet was the grandest of the 19th century in point of size and brilliancy. Fig. 194 PLATE LIX. Coggia's Comet, 1874, on July 13 (F. Brodie). 106 Fig. 196 PLATE LX. The Great Comet of 1862 (Cnutus). [106a] Figs. 197-198 PLATE I.XI. A black and white photograph of a comet with a bright nucleus and a long, faint tail extending to the right. Nov. 15 The Great Comet of 1882. Nov. 2 1661 Figs. 199-200 PLATE LXII. A black and white photograph of a comet's head and nucleus. The head is a bright, elongated shape with a smaller, more diffuse nucleus attached to its base. Nov. 15. A black and white photograph of a comet's head and nucleus. The head is a bright, elongated shape with a smaller, more diffuse nucleus attached to its base. Nov. 17. The Head and Nucleus of the Great Comet of 1882. Figs. 201-202 PLATE LXIII. A black and white photograph of a comet. The comet appears as a bright, elongated object against a dark background. 166D] PLATE LXIV. Figs. 203-204 The Niblons of the Great Comet of 1882. March 5, 1883. Feb. 17, 1883 [607] CELEBRATED COMETS. 167 DONATI'S COMET, 1858 (vi.). This comet, though inferior in size, as just stated, to the great comet of 1843, may be regarded as having been the most beautiful of all comets, owing to its perfect roundish shape, and to its possession of certain long, straight streamers not reproduced in the engraving. The star visible near the comet's head is Arcturus. THE COMET OF 1860 (ii.). This comet was not one of very remarkable size, but the pictures are given for the reason that they exemplify in a striking degree the jet-shaped emanations which occasionally are noticed to proceed from the head of a comet. This feature was not brought out in a very marked manner in the comet of 1862 (iii.). COGNITI'S COMET, 1874 (iv.). Cogniti's Comet of 1872 may be described as a good specimen of a second-class fine comet. It was a striking object in the evening sky during the month of July, but it is engraved in this book as being a good example of the way in which some comets seem to shed off independent envelopes, or shells of matter, once after another. THE GREAT COMET OF 1882 (iii.). This was a naked-eye comet with no tail at all much in the shape of a Turkish crescent. The main tail gave one the impression of being inside a long and wide, but very ethereal or filmy, envelope. But the special feature of this comet was its nucleus, which was and still is unique in its form. It was elliptical, and of great length in proportion to its breadth; it 168 COMETS. was placed longitudinally with regard to the general direction of the tail ; and, to crown all, instead of having the usual one special bright centre, it was always seen to have three bright centres, sometimes four, and on one occasion a fifth was suspected, all of them a little distance from one another. Swift's Comet, 1892 (c.) We have passed now from the epoch of hand-drawn pictures of comets to the more recent era upon photography. Whilst it is, of course, a truth that the Sun is a refracting telescope - man than the human eye and hand together, it must be confessed that photography often fails to bring home to the eye many details which sometimes strike even the most inattentive observer. But this cuts both ways, because not only is the case of comet photography different from that of photography from telescopes features which are invisible, not only in the telescope used by a particular observer, but in all telescopes, whatever may be their size. It was owing to photography that Swift's Comet was discovered. The photographs show us the tails of comets which may be said to have revolutionised our ideas as to the physical condition of those bodies. Barnard well remarks that "the discovery of Swift's Comet was made by an older method of observing would have promised little or nothing of interest." Swift's comet may be mentioned as one of those which seemed to be endowed with a rotation of the head and tail about an axis passing longitudinally through the tail. Rordame's Comet, 1893 (ii.,) illustrates a remark in the last paragraph about photography, bringing out details not readily grasped by the naked eye, for some of its peculiarities are of the same sort as those of Swift's Comet. PHOS. 205-208 PLATE LXV. April 7. April 12. June 30. April 16. Swift's Comet of 1869 [A.L.] Figs. 209-212 PLATE LXXVI. April 13. April 14. April 15. April 16. Swift's Comet of 1892 [L.] 258a Figs. 213-214 PLATE LXVII A starry night sky with a bright comet-like object moving across the frame. 1088] July 4, 1895. Redman's Comet of 1895 (ib.), (W. J. Hruby). [Photograph of a comet-like object in the sky.] [Photograph of a comet-like object in the sky.] Figs. 215-216 PLATE LXVIII Oct. 31. Oct. 22. Brooks's Comet of 1893 (iv.). 168 Fig. 217 PLATE LXIX. Borelly's Comet of 1903 (iv.), (R. J. Wallace). 168f) Fig. 218 PLATE LXX. A starry night sky with a comet visible in the center. Desc. 03, 1905. Giacobini's Comet of 1906 (L.), (E. E. Barnard). 1488 Figs. 219-220 PLATE LXXI. Dec. 29, 1905. Jan. 5, 1906. 1887 Glacobin's Comet of 1906 (L.), (E. E. Barnard). FIG. 221 PLATE LXXII. A comet with a bright tail, surrounded by stars, photographed on a clear night. The Halley's Comet, Nov. 7th, 1835. The photograph was taken at the Royal Observatory, Greenwich. [146] REMARKABLE COMETS. 169 Brooks's Comet of 1893 (iv.). This seems to have been a comet damaged by some external violence, strange as the idea may seem. Barnard wrote thus about it:— "Indeed, the singular freaks of that comet's tail compel us to seek an explanation in some outside cause--inherent neither in the comet itself nor in its immediate environment. The tail was a normal condition, was on the next brooks and disturbed, as if it had encountered some resisting medium in its flight through space. It was not a tail which moved in any direction towards which the comet was moving. On the suc- cessive days after its appearance, the tail became thicker and heavier, some of which were entirely torn off from the tail and appeared to be drifting away in space. On another occasion the tail was seen to be being beaten against a current of resistance. It was then observed that the comet itself was moving at nearly a right angle, as if at that point it had encountered a stronger current of resistance. If one examines these pictures one finds that the comet itself was moving at an angle with the tail, and that the comet's tail did actually encounter some resisting or disturbing medium in its course. This is not a new idea, but I am writing this date; whether this was a swarm of meteors--such as we know exist in space near the Sun, or some sort of resisting matter, of which we are yet ignorant--is a subject for time to settle." BROOKS'S COMET, 1905 (i.) This comet justified me in my assertion of a curious nature--that is to say, signs of a part of its tail having actually broken off from the main tail; which latter, after losing the aforementioned fragment, began to grow again in consequence of a new supply of matter being forthcoming from the nucleus. GACOBSON'S COMET, 1906 (i.). Observations of this comet were unfortunately much interfered with owing to the prevalence of bad weather; but, notwith- 169 170 COMETS. standing this, Barnard got some good photographs of it, and was also able to make some striking notes. He says that the comet's appearance on December 29, 1905, was— "in some respects quite unique. From a rather large head at the tail end, the comet gradually tapers off into a side in graceful curve, which very closely closes in upon and gives a strong convexity to the tail. The edges of these concavities are so smooth that they are scarcely visible, either in profile or border. The appearance of the tail strongly suggests a straight edge placed along the sides of the plate. This straight-edge placed along the sides of the tail shows this convexity strikingly, as may be seen on an examination of the plate, I have not noticed quite this appearance before in a comet's tail." DANIEL'S COMET, 1907 (iv.). The original negative of this comet showed the tail to have no branches, but, owing to the extreme faintness of two of them, only one branch is visible in the photograph near the end of the tail with a black dot in it was Y Geminorum. MOREHOUSE'S COMET, 1908 (ii.). This comet, though not in itself a very large one, attracted considerable notice in the astronomical world owing to the transformations which it underwent. The two pictures, both dated October 15, taken, one in England and the other in America, show how much its appearance changed during the time between them. It is clear from these pictures that the cause of this excitement. Barnard's photograph vividly brings out the fact that the tail of the comet underwent a serious and real disruption. HALLEY'S COMET, 1910 (ii.). So much has been said already about Halley's Comet that it seems only necessary here to remind the reader that it was only in the Southern Hemisphere, and after the comet had Fig. 222 PLATE LXXIII A starry sky with a comet-like object moving across it. On Oct. 15, at 14 h. 37 min. Morehouse's Comet of 1908 (BL); (E. E. Barnard). cp] Figs. 223-224 PLATE LXXIV. Oct. 15, 14 h. 34 m. G.M.T. Nov. 15, 12 h. 6 m. G.M.T. Morehouse's Comet of 1908 (IL), (Yerkes Observatory). [179a] FIG. 225 PLATE LXXV. A comet with a long tail against a starry sky. Morsehouse's Comet of 1908 (III.), on Nov. 13. Figs. 236-239. PLATE LXXVI. May 25. May 27. May 28. June 2. Halley's Comet, 1910 (C. H. Gingrich). Fig. 230 PLATE LXXVII. A faint comet with a long tail is visible against a dark sky. Below the comet, there is a landscape featuring palm trees and a desert-like terrain. The Daylight Comet of 1911 (W. B. Gibbs). As seen in North Africa. 1706 Plate LXXVIII. Fig. 231-232 Brookly Comet of 1911 [F. W. Langenheim]. 171 REMARKABLE COMETS. 171 passed by perihelion, that the most striking views of it were obtained. Hence it comes about that the pictures here given may excite distrust as to their accuracy on the part of dwellers in the Northern Hemisphere. **BROOKS'S COMET, 1911 (c).** The picture dated Sept. 24 [Plate LXXVIII.] brings out the fact that the comet has a very long tail, with a very slender tail preceding from it. The photograph vividly recalls to my mind one of the earliest comets I ever saw, I am not certain of the exact name and date, though I think it was one of the earlier comets of 1857, discovered by Klinkerfues at Göttingen on August 20. By way of a last word, it may be well to explain why, in making these photographs, we have not used the structure given in this volume show as streaks and not as points. It is because the several comets being themselves in motion, it is necessary to take them at different times (in order to get good views of the comets), that the driving-clocks of the telescopes employed should be timed to keep pace with the comets rather than with the diurnal movement of the stars. CHAPTER X. SHOOTING-STARS. Various classes of luminous meteors—Shooting-stars—Fireballs—Aireolites—Radiant points of shooting-stars—Amount of the most conspicuous radiant points—The most brilliant radiant points—Historical allusions.—Celebrated great showeri... Fireballs are the most conspicuous of the luminous phenomena described by writers on meteorology. They are remarkable fireballs described by W. H. and Brodie.—Their sizes, distances, and motions are very various. The difference between meteors and comets.—Shooting-stars, fireballs, and airoelites all of the same nature.—Circumstances attending the fall of airoelites. "SHOOTING-STAR" is the popular name for a celestial object which is scientifically called a meteor. This body is luminous because it is subdivided into small luminous meteors and fireballs, with what are called airoelites thrown in. Though the first two subdivisions are visually closely allied, they are distinct in their properties. The airoelites are so in reality. A simple shooting-star is just exactly what its name imparts at first sight—a star which shoots; yet it is not a star at all. Postponing for a while a consideration of the nature of all these bodies, we will first of all consider how and when they show themselves to us. We have seen them in every clear night throughout the year when the air is transparent and the Moon is absent. Thoughtlessly looked at, the observer will fancy that they dart forth constantly in the sky, first at one point and then at another point; but such is not the case. It is true that these isolated meteors 125 Fig. 233 PLATE LXXIX. A Meteor in Flight (E. E. Barnard). [The object gradually increased in brilliancy, and as gradually faded out, ending in two short flashes of light.] Fig. 234 PLATE LXXX. Fishing for Meteors without an Equatorial (F. W. Langford). [19] TELESCOPIC METEORS. 173 used to be thought independent of one another, and they were formerly called " sporadic" meteors, which meant that they were haphazard occurrences, but this designation has now, however, lost nearly all its importance and significance, because the prolonged observation which has been given to them during recent years has enabled astronomers to realise that they belong to families, each family having its own centre in the heavens, which is designated by the term " radiant point." The recognised radiant points are not very numerous, im- portant ones being only about a hundred in number; but of these the majority are so weak not to attract notice except at great and patient attention. On the other hand, there are a certain few radiant points of which, at definite dates, and in great numbers, shooting-stars emanate; and it is to these that I will in the first instance direct the reader's attention. The Perseids are an example of such stars is undoubtedly that named the Perseids, because they belong to the constella- tion Perseus and show themselves on or about August 10. Diagram showing a circular diagram with radiating lines from a central point. The diagram is divided into four quadrants labeled E (East), N (North), W (West), and S (South). The text around the diagram reads: "belong to families, each family having its own centre in the heavens, which is designated by the term 'radiant point.' The recognised radiant points are not very numerous, important ones being only about a hundred in number; but of these the majority are so weak not to attract notice except at great and patient attention. On the other hand, there are a certain few radiant points of which, at definite dates, and in great numbers, shooting-stars emanate; and it is to these that I will in the first instance direct the reader's attention. The Perseids are an example of such stars is undoubtedly that named the Perseids, because they belong to the constellation Perseus and show themselves on or about August 10." Fig. 235.--Flight of Telescopic Meteors (Brooks). 174 SHOOTING STARS. Meteors may be noticed some days before and some days after the period date just mentioned. They come from a very rich annual shower of swifthy, white meteors which have no marks behind them. The approximate centre of the shower is to be taken at a point 4° N.E. of the star ζ Persei; say, Right Ascension 13 h. 50 m., and Declination 44° N. This takes place November 23. The next most important shower is that appertaining to the constellation Andromeda, and known as the Andromedids, with the radiant point about 4° N.W. of the star ζ Andromedæ; say, Right Ascension 13 h. 40 m., and Declination 44° N. This takes place December 8. The third most important shower, may be said to belong to the Lyrids, belonging to the constellation Lyra, with the radiant point about 8° S.W. of a Lyre; say, Right Ascension 18 h., and Declination 33° N. These meteors move swiftly, and the brighter ones are seen for several days. Date—April 20. The last few paragraphs give us only the more im- portant showers, arranged in the order dates from January onwards. January 2, the Quadrantids, belonging to the constellation Quadrans. The radiant point will be found about 12° N.E. of Bootes; say, Right Ascension 15 h. 20 m., and Declina- tion 6° N. This takes place February 18. July 28, the Aquarids, belonging to the constellation Aquarius. The radiant point will be found about 5° N.W. of Aquarius; say, Right Ascension 23 h. 36 m., and Declination 12° S. This is an annual shower, with recurring meteors which may be dependent upon its recurrence. October 18, the Orionids, belonging to the constellation Orion. The radiant point will be found about 10° N.W. of Orion; say, Right Ascension 6 h. 8 m., and Declination 15° N. This is a very rich shower, which occurs every year, and though dated for October 18, watch for it should begin on October 9th, and continue till October 25. November 15, the Leonids, belonging to the constellation SHOWERS OF METEORS. 175 Leo. The radiant point will be found 3° N.W.N. of y Leonis say, Right Ascension 10h., and Declination 1° N.; this is a great historical shower, having produced occasional displays in 1799, 1833, and 1866, and did not reappearance in its pristine splendour, as was confidently expected, in 1899. A slight dis- play may be expected every year between November 9th and December 2nd. November 20, the Taurels, belonging to the constellation Taurus. The radiant point will be found 5° N.W.N. of y Leo; say, Right Ascension 4 h. 8 m., and Declination 1° N.; This is a well-known shower of slow meteors. December 10, the Geminais, belonging to the constella- tion Gemini. The radiant point will be found 3° W.N.W. of y Geminius; say, Right Ascension 7 h. 22 m., and Declina- tion 3° N. It will be understood that the showers enumerated in the preceding paragraphs are those which may be regarded as the most notable; but, as has already been stated, shooting- stars are seen at all seasons of the year, and at all latitudes, every night in the year. It would take up too much space in these pages to specify, and state the positions of, even a title of the other recognised radiant points ; but observations of them have been made by many observers, and are of interest to amateurs as a very interesting study, the fruits of which, if collected and tabulated with care, will be very useful in pro- motion of scientific astronomy. Darwin has remarked that brilliant meteors often emit a shower of the scattering Scopio in the month of June. This might be a suggestion worth following up. Such showers have been in the pages of history, and have done so from ancient times. One of the earliest allusions to them dates from A.D. 472, when they were told by Theophanes, the Byzantine historian, that "the sky at Constantinople seemed to be on fire with flying meteors." A remarkable dis- play took place in England and France on April 4th, 1905, when 176 SHOOTING-STARS. the stars seemed to be "falling like a shower of rain from heaven upon the Earth." The first great star-show, display on November 13, 1793, visible throughout America, and of which Alexander Humboldt has left a thrilling narrative; but the greatest display on record appears to have been that of November 18, 1833. The 1833 show was visible nearly the whole of North America, and, from the accounts which have reached us, it must have been one of imposing grandeur. The people who saw it were alarmed, especially the Negro population, were terror-stricken, such was the beauty and magnificence of the spectacle presented. The following account is from the pen of a planter in South Carolina: "I was suddenly awakened by the most distressing cries that ever fell on my ears. shrieks of horror and cries for mercy I could hear from every part of the house. The noise was immense, amounting to about six or eight hundred. While earnestly listening for the cause I heard a faint voice near the door calling out, "Come here, come here." I went to the door. At this moment I heard the same voice still beseeching me to rise and come in. I entered the room. There I found them all in a state of consternation. They said they had never seen anything so terrible before. They told me the reason--and it is difficult to say which excited me the most--the awfulness of the scene or the distressed condition of those who witnessed it. It was a scene of confusion on the ground--some speechless, and some with the bitterest cries in their throats. They said that they had never seen such a sight in all their lives. The show was truly awful; for never did rain fall much thicker towards the Earth. East, west, north, and south it was everywhere. Though there are spokes of shooting-stars as being visible almost always everywhere, this statement must not be taken to imply a uniform distribution over the heavens, because it is evident that in certain hours of Night Ascension (that is, in the constellations occupying those hours) there are more centres of meteore-creation than in others. In other words, A page from a book showing text and illustrations. RADIANT POINTS OF METEORS. 177 that meteor-centres are most abundant in the first 4 hours of R.A., whilst they are fewest in the hours between X and XIV. In the Northern Hemisphere, where the moon may be seen in the declinations, there seems an obvious maximum between 41° and 60° of North Declination. These results are due to the un- tiring industry of Denning, who was our principal m e t e o r observer. Unfortu- nately, no corre- sponding stat- istics are available for the Southern Hemis- phere, because luminous meteors have never been catalogued and studied there as they have been in the Northern Hemisphere. Dissecting the year by months, it has been found that an overwhelming preponderance of meteors are associated with the month of August; indeed, the two months of July and August together provide 50 per cent of the total number of meteors catalogued during the 12 Fig. 238.--Meteor Radiant Point in Gemini (Dec. 12) on Nov. 28--Dec. 9, 1864. A diagram showing a radiant point in Gemini at a specific date. RA & Decl. 178 SHOOTING-STARS. past half-century that systematic observation of luminous meteors has been carried on. The chief aim of a recent point, and in some sense the details of the observations which, under ordinary circumstances, can be carried out in connection with it, will better be realised by examination of a plan (Fig. 25), showing the marked difference between the two cases having been seen emanating from the initial point in question. Fig. 25a represents an arrangement devised by Mr. F. W. Lees, who has made many observations of the meteors. He arranges in a row several rapid cameras and takes his chance of their being able to catch any meteors which may dash themselves against the camera-screens. The stars, as they pass through the field of view, leave trails on the plates, but these do not matter, as their streaks can never be mistaken for the streaks which a meteor would leave, the difference between them being that the former are produced by light commencing and finishing the exposure is noted, a man of the stars recorded on the plate can be made by pecking at their positions on the screen, and then taking a photograph. A good plan to stop exposure when a meteor is seen to cross the field covered by the cameras-lens; then the end of each star-trail shows the position of the stars at the moment the photograph was taken. It is desirable that the exposures should be made so that the star-trails (or most of them) begin and end on the plate, though, of course, this is not always possible. The time at which the meter is seen should be noted, and also, of course, any other particulars deserving to be recorded. We have now proceeded to consider the question of Fireballs. It is doubtful whether any particular distinction can properly be drawn between shooting-stars and fireballs, or that there is any distinction at all between them excepting that of size, to which perhaps may be added that of duration of visibility. The grounds for this assumption of identity of FIG. 237 PLATE LXXXI. The Milky Way Field Pencil Drawing. (Reproduced from the Greenwich Observatory, Nov. 15, 1864.) Figs. 238-247 PLATE LXXXII. A series of photographs showing meteor trails at New Haven, Conn., Palisades, N.Y., Haverford, Pa., and Williamstown, Mass., Nov. 14, 1886. **NEW HAVEN** **PALISADES** **WILLIAMSTOWN** Meteor as seen at New Haven, Conn.; Palisades, N.Y.; Haverford, Pa.; and Williamstown, Mass., Nov. 14, 1886. Fig. 346. First View. Fig. 346. Second View : (73), Aug. 18 (Sandy and Robinson). Fig. 350. 1826, June 7 (Dawson). Fig. 351. 1865, Oct. 29 (Schmidt). Fireballs. 180 SHOOTING-STARS. origin and nature between the two classes of bodies now under consideration depend on the fact that various meteor-showers, such as the Fernsels, are composed of many others, whilst much of the light of star-like points of light and again yield meteors of great brilliancy, comparable alike in size and brilliancy to the isolated objects which are specifically A diagram showing the formation of a meteor trail left by the Fireball of Oct. 19, 1877. Figs. 252, 253.—Curious Form of Trail left by the Fireball of Oct. 19, 1877. 1. First effect. 2. Second effect (20 min. later). termed "fireballs." Speaking generally, of course, it must be conceded that the latter are more numerous than the former in size and importance to get into the newspapers appear in the heavens singly, and, though usually noiseless, sometimes are seen to burst, making a great noise. In this case they are generally pear-shaped. When moving slowly they usually give FIRE-BALLS. 181 forth trains of sparks, which either disappear promptly or sometimes linger for many minutes, and drift slowly away, apparently under the influence of currents of wind high up in the atmosphere. There is a strong family resemblance between all fireballs, and a drawing of one would be typical of a large number, as will be realised by an examination of the illustrations here A drawing of two fireballs with trails of sparks. Fig. 254.---Successive Changes in a Fireball during its Visibility. given. As good a description as could be had of an average fireball will be found in the following account of one seen by the Rev. T. W. Webb on November 12, 1861. He said :-: "We were walking, a party of three persons, along a wide turnpike road, fully lighted by a Moon 10 days old, when we were suddenly struck with a very bright object in the sky, not like lightning, but rather resembling the effect of moonlight suddenly coming out from behind a dark cloud on a windy 182 SHOOTING-STARS. night. It fadid very speedily, but on looking up we all per- ceived, at a considerable altitude, perhaps 60 or 70', a superb mass of fire sweeping onwards and falling down towards down the W.S.W. sky. Ruddy clouds of a sort of glowing coals, were seen to be moving at a smaller end, and its path was marked by a long line of smoke of little permanency. Its movement, however, fortunately, was con- cealed by boughs of trees; and though, however, it was traced till possibly 30 miles above the horizon, but it had previously undergone a great diminution. The whole duration of it must have been as much as five seconds. Its supposed velocity was that of a lighted and indifferent candle. The immediate im- pression was that of rapid descent. The following description of the luminous track of a large meteor on February 25, 1909 (which seems to have been indeed a fireball), and was widely observed along the S. coast of England, is from the pen of Mr. C.G. Brodie. The meteor was quite unique, I think, in the astonishing length and Fig. 255.--Meteor of Nov. 12, 1861 (Ward). on February 25, 1909 (which seems to have been indeed a fireball), and was widely observed along the S. coast of England, is from the pen of Mr. C.G. Brodie. The meteor was quite unique, I think, in the astonishing length and Image of a black and white diagram showing a path of a fireball observed in the Isle of Wight, Feb 22, 1909 (C. G. Broddy). 356 184 SHOOTING-STARS. vagaries of the trail which it left behind. He says that on the day in question— " While crossing to the Isle of Wight from Portsmouth, my attention was called to a luminous streak in the southern sky, I think at about 6 p.m., and continued for some time after, about 7-30 p.m. as we were leaving the harbour. The trail, which was very bright, appeared to be composed of two parts under α and γ Orionis as a plain luminous streak somewhat laminated in structure. Passing from W, to S, it entered Orionis, where it became a continuous line of light, then receding into one of brightness, above a Kriadiani; and then passing S., it became fainter and more diffuse, but still white, round, luminous nucleus. From this another streak stretched directly eastwards, passing under the two lower stars of Orionis, and then turned northwardly towards the pole. The commencement of the upper streak between Procyon and Sirius was seen to be bent into a loop, the cusp being downwards. Before we reached Ryde (say 7-55 p.m. to 8 p.m.), the upper limb had diffused round vertically, and the lower limb had become less distinct. The lower limb was less acute, and the nucleus disappeared, the lower streak descending towards the pole. At 8 p.m., when we arrived at Ryde station, there was no trace of any fireball whatever." As an example of the kind of observations made by ordinary people during the night of July 2nd, I may mention what several persons told me on the following morning. Several people told me that the fireball was so brilliant as to resemble a star. Others said that it was like a comet. Some saw it shining brightly in the sky, others saw it moving slowly across the heavens. This shows that the meteor must have been exception- ally bright, as the sky was clear and there was a young Moon. The next day I went to see Mr. Hutton at his observatory, who suggested to me that it might be drifting by the action of the wind. The meteor was observed to register on S.E., and the day following was still easily seen. It has been found that certain dates may be stated at which fireballs may specially be looked for. The following are some of these dates: January 2, February 7, April 11-13, 19-20, June 6, July 25-29, August 1-7, September 1-2, 6-7, November 1-9, 6-9, 11-15, 19-20, December 5, 11-15, 21.
PATHS OF FIRE-BALLS. 185 Attempts have often been made to subject particular fire-balls to computation as regards their distances, sizes, and velocities, but the results have generally been found to be of very limited utility of these movements and of the changes which they undergo render the results in all cases very uncertain. Subject to this view it may be stated that their height above the ground varies from 300 feet upwards to 10,000 feet or more, up to 80 miles or more; their absolute diameter between perhaps 60 yards and 2 miles; and their velocity between 2 miles and 100 miles per hour. The last-named is by no means unusual in the case of particular fireballs. It may be remarked, however, that one is apt to exaggerate estimates of diameter, and also of velocity, measured in the first instance as so many feet per second, and in the second as so many miles per hour, on which trustworthy results can be assured are in the instances, naturally very rare, in which two trained observers in widely separated places have observed the same fireball at the same time. It is fortunate to see the same fireball start on its career and be able to follow it to the end. There are a few instances of this on record, and the calculated results may in such cases be, to a certain extent, correct. There must now be mentioned a matter connected with celestial mechanics, which might with equal propriety be called "the problem of fire-balls." I allude to the modern discovery of the association between certain comets and certain displays of luminous meteors. The connection has been known for some time. Although it is far from easy to pronounce dogmatically on the circumstances so far as they are yet known. The simple fact, concisely expressed by Sir William Herschel, that the Sun is always in a closely revolving orbit around the orbits of certain comets that we are driven to the startling conclusion that some of the recognised meteor-showers are either off-shoots from comets or are the actual materials of disintegrated comets. There is, at any rate, one instance of this which is hardly open to serious doubt. A diagram showing the orbits of comets and meteor-showers. 186 SHOOTING-STARS. question. The former well-known Comet of Bieha has abso- lutely disappeared, but there exists a swarm of meteors travelling round the Sun which present themselves every November, and which have been observed by many observers, which pursue a path practically identical with that which used to be followed by Bieha's Comet, so long as we knew it as a comet, but since the conclusion is inevitable that the comet, as it originally was, has been broken up and become a swarm of meteors. Whilst it is obvious that such a conclusion sets us all thinking it is not easy to say how far, or in what direction, our thoughts ought to go. The following is a summary statement of the association of certain comets with certain meteor-showers :
Comet Meteors. Date.
Tolstoy's Comet Radianes Pott April 20
Halley's Comet Aquarius May 1-6
Tupeu's 1866 (i) Leonids Leo Nov. 13
Bieha's Comet Andromedens Andromeda Nov. 27
The circumstances of Tempel's Comet are specially remark- able, as they have given rise to a very full discussion on the wood, some details of which interest the reader. It has already been stated in an earlier part of this chapter that the Leonid meteors first attracted the attention of a scientific observer in 1799, and that the showers continued until 1833. The Leonid shooting-stars seen in 1799, 1833, and 1866 were periodic manifestations of the same shower ; but it was not till near the beginning of this century that any idea of a certain comet with this shower became fully understood. The subject was started in its first development by the dis- covery, on December 19, 1852, of a small comet by Tempel, then at Marseille. It was generally observed for seven weeks, and although not a very conspicuous object, its relations to the THE LEONID METEORS. 187 Earth and Uranus may be said to have given it an importance surpassed by very few others. The final computation of its period showed that it was a **periodical** comet revolving round the Sun in 3328 years. This comparatively short period led to cata-logues of comets being searched, and it was found that, when reckoning backwards 3328 years a. c., at many times, there were coincidences (with back to the year 405 b.c. of which might be identical. If one can assume that such a date may be safely taken as a terminus a A diagram showing the orbit of the Leonid meteor shower around the Earth. The diagram includes labels for "Orbit of Certain Planets" and "Orbit of Earth." There are also labels for "Orbital Satellites" and "Orbital Satellites." Fig. 257.—Orbit of the Leonids of Nov. 13 and 14, A. C. 405, when it might be identical. If one can assume that such a date may be safely taken as a terminus a 188 SHOOTING-STARS. quo, we have, as a result, 73 periods of 33:28 years down to A.D. 1560. A comet in 1366 is regarded as another absolutely certain terminus a quo for later centuries. From 1660 to 1866 it is only 47 years, and from 1866 to 1960 it is only 29 years. Professor H. A. Newton, working on independent lines, traced back the great showers of 1866 and 1833 to A.D. 902. He showed that the shower of 1866 was due to a comet which passed through the swarm round the Sun, namely, 18 days, 15 days, 35 days, 377 days, or 334 years. This important uncertainty was, however, first definitely solved by Professor J. C. Adams in 1867, who found that the period of the comet was about 3325 years. The conclusion that Tempel's Comet and the great meteoric shower of 1866 were connected with one and the same comet was reached because it was known that the swarm of meteors was in fact derived from the comet, and was reached almost simultaneously by Peters, Le Verrier, and Schiaparelli; but the matter was carried a good deal further by Kirkwood. He showed that a clear connection existed between the comet and also of a third cluster belonging to the same family, moving in orbits clearly identical in form with those of the comet and the third cluster. The existence of such a close connection between these two distinct groups of coincidences has thus been brought to light. I have not space to go into further details, but Kirkwood gathered up from a long series of observations of meteors during the last few years evidence that there exists a family of comets which furnished him with the information on which he based his conclusions. We will pass now to the consideration of asteroids, and this brings us face to face with the important questions which I have not yet broached: What is a shooting-star? What is a fireball? Whence comes an asteroid? I think it must be said that these questions must be answered together, and that A diagram showing three clusters of asteroids. A rocket's exhaust plume during a launch. U.S. Navy/NASA Lentils of colored paint in a stream traced by a rocket, for D. H. Munsell [API_EMPTY_RESPONSE] AEROLITE. 189 The cojoinant answer must be that all these bodies are, or have been, masses of solid matter floating about in space, coming from whence we know not, but which, when they reach the Earth's atmosphere at about 80 miles above the Earth's surface, (1) fall to the ground as stones, (2) take fire and burn, (3) fall to the ground as sooty smoke, or (4) stone, which are either in their original form and of their original size, or which, when we see them on the ground, are the broken-up fragments of some larger body. The first three cases are very rare; the fourth is more common. The last case is found in the upper regions of our atmosphere or farther off in space. With aerolites we rather pass from the domain of astronomy into that of physics and chemistry, and therefore my treatment of the subject in these pages will be brought into somewhat narrow limits. The crucial fact which we have to bear in mind is that now and again stony or semi-stony meteoric bodies, composed of various materials, fall on the Earth, from whence we know not. The number of such falls, recognised as such, has now reached a considerable amount. It is estimated that there are 5000 such areas; that is to say, that instances of such falls have been recorded at many dates, beginning with more than 2000 years ago. In this way we get a fair idea of how every part of the habitable globe is covered by meteoric matter. But many aerolites have been transported by the hand of man from the place where they fell to some neighbouring or distant public museum. Hence it comes within our power to examine them under the microscope in the British Museum and in many other public museums in different parts of the world. Naturally, most of the aerolites which have fallen upon the Earth have been examined chemically and their terrestrial origin had to be inferred from analogy and chemical analysis; but a few cases are on record in which the aerolite was seen to fall, and was examined by an eye-witness and described by him in his own words at the time of its point. On April 20, 1876, a mass of meteoric iron weighing about 7 lbs. fell at Rowton, in Shropshire. We are told that shortly 100 SHOOTING-STARS. before 4 p.m. a sound like that of thunder, followed by reports as of cannon, shook the air, and was heard during rain-showers for many miles round in that neighbourhood. No fireball was observed. The iron was found about an hour afterwards in a mass of earth, which had been dug with a depth of 18 inches. When dug out it was still quite hot. In the foregoing case the material was metallic, more or less, but in the following case, and mainly, the material has been generally stone of several other kinds, consisting mostly of composition or a mass somewhat basaltic in its nature. It is obvious that opportunities for actually observing the fall of an asteroid are very rare, but what we can do is to study their appearance and investigate their chemical composition in the light of the facts gathered up for us as regards the time and place of their fall. CHAPTER XI. THE STARS. The apparent movement of the stars on a starlight night.—The stars are luminous bodies, and their light is due to their con- sequences.—The stars visible vary with the latitude.—The expression "looked at" is used in astronomy for "seen."—The identification of the stars.--Bayer's system of lettering stars.--Emanation of light from the stars.--Number of naked-eye stars.--Amount of star-light.--Twinkling.--Inclination of the axis of rotation.--Different colours.--Triple and multiple stars.--Variable stars.--Notable contemporary stars. We are now starting on what is obviously a very large subject, and one which has numerous ramifications, and I propose to treat the subject in two broad divisions, that in the order in which the student of the stars would be likely to approach the subject, first of all as an observer using only his eyes, and then proceeding to employ an object-glass, a small telescope, and finally a large telescope. The dominant idea which will run as a thread through this and the later chapters dealing with the constellations will be that the reader will find it useful to study the stars by actual geography (though this is not the proper word) of the heavens, with the view of knowing what interesting objects to look for and where to find them. ¹ It should be "astronomy," from Oosseu heaven, and 30epo, I write, 30 192 THE STARS. I will now proceed to deal with a variety of general con- siderations relating to the stars, individually and collectively, including their apparent movements through the different seasons of the year. Some of these topics may seem to be dry, but clear conceptions as to many of them are of prime im- portance. Everybody, I suppose, knows that the Earth turns on its axis as a wheel turns on its axis. The visible consequences of this ac- tion are seen in the daily rising and setting of the sun, moon, and by the reader taking his station on a clear, starlight night in some high and fairly open position facing the N., but with a view towards the S.W. and W. This being done, he will at first instance, try and fix in his mind the grouping of the stars in the W., somewhere about the point where the Sun has set. Next let him turn his eyes and take note of the stars which are now visible in the W. Let us examine the stars due E. of his position, and fix in his mind their general appearance. Let him reckon stock as it were, of these three portions of the heavens, let him go indoors for an hour, or better still, for a couple of hours, and then come out again and refresh his memory by trying to recall what he had observed. It will be found that with great difficulty in doing so. Several of the principal stars which he had previously noted as low down in the western horizon will have disappeared. Those which had been seen in the eastern sky will have moved up into the W., whilst when he directs his eyes to the eastern horizon, he will discover a fresh set of stars which he had not seen before. He will find that he had seen having visibly risen higher up towards the zenith. If, instead of coming out a second time the same evening, the reader had postponed for a week his next inspection of the heavens, he would find that all the stars which had been the aspect of affairs. Every group of stars would have moved on ; those which had been in the W. would have dis- APPARENT MOVEMENTS OF THE STARS. 193 appeared, and a new assortment would have started up in the east. If, instead of resuming his work in a week, he had continued to observe for another month, the results would have been even more radically different; and, to cut a long story short, if he had prolonged his study of the sky by only looking at it once a month for 12 months, he would, at the end of that time, have seen no change in the stars, but still indefinitely A diagram showing three views of the same star at different times of day. The top view shows the star at Calmation 3 P.M., with the sun rising on the left. The middle view shows the star at 6 P.M., with the sun setting on the right. The bottom view shows the star at 9 P.M., with the sun setting far to the right. The text "NORTH" is written below the bottom view. Fig. 259.—Apparent Changes in a Group of Stars in the Course of 12 hours between Rising and Setting. the same positions in which they had been on the night of his first observation. But this was not all; for what would have happened would have been this: he would have had under notice all the constellations, and therefore all the stars, which under any possible circumstances could be seen in the latitude of his place of observation. The mention of the word "latitude" opens up a subsidiary 13 194 THE STARS. matter of great practical importance. In consequence of the axis of the Earth being inclined about 23° to the ecliptic (the apparent path of the Sun), the whole body of stars need to be considered under three heads:— I. Those in the neighbourhood of the Poles which never go below the horizon, but which are visible on every clear night throughout the year. II. Those which I have first described, which come into view and pass out of view, being obliterated in turn by the Sun's rays, and whose annual course passes through the signs of the Zodiac; and, III. Those which he towards the S., including those which gallop across the sky at night, and which are generally concealed from the observer in a given northern latitude. The foregoing statement respecting the visibility of particular constellations will be found useful in navigation. In the first place, if the observer in the first-mentioned latitude say London, proposes to travel to the North of Scotland, he will lose some of the stars which, in the latitude of London, he glanced at when they were passing along his extreme northern horizon. If, on the other hand, he moves away from London to the extreme South of France, and then travels northwards to southern Britain, all stars of the existence of which he had obtained no knowledge when at his original station in the latitude of London, will appear to him as though they had gone away 6000 miles to the Cape of Good Hope, or on to Australia; he will come face to face with an entire reversal of everything which he had seen when in the latitude of London. The Northern Cross will disappear, and all its constellations in their neighbourhood would have disappeared irrecoverably. The constellations which had passed over the sensible London horizon during his journey southwards, and which were previously visible North Pole, and its Pole-star, will have disappeared, and been replaced by another Pole, and another THE STARS AS SEEN IN DIFFERENT LATITUDES. 195 Pole-star,¹ and an entirely new set of constellations will pass over the zenith at the Cape and in Australia, so that in point of fact the aspect of the nocturnal heavens will have become considerably altered. The statement just made as regards the consequences of an observer transferring himself from London, in the North latitude of 51°, to a place in the South Hemisphere, which would be somewhat to the S. of New Zealand, may be otherwise expressed thus: that the stars which are within the "circle of perpetual apparition," and which are perpetually visible in England, will be perpetually invisible in New Zealand, and the stars which are perpetually out of view will be perpetually visible in New Zealand. But this statement must be understood that it literally true in substance, depends on identical latitudes being compared, and that the latitude of 51°, which is assumed to be that of London, is only a little distance S. of the most southerly point of New Zealand. It must be that the foregoing statements as to the changes in the aspects of the heavens which will be noticed by an observer watching the stars from night to night throughout a period of several years, are not mere idle intellections; and that what is meant is truly the whole vault of heaven with its whole body of stars is in constant movement as an unchanging whole. But this presentation of the matter, though convenient and indeed necessary, is not quite correct. It is true it is one of those conventional truths which are often useful in astronomy as a preliminary to pave the way to precise Whilst the Northern Hemisphere has, as its representative Pole-star, a fairly bright star (a Uran Minoris), which is very close to the exact polar position; but in the Southern Hemisphere there is no star nearest to the South Pole (e Oortia) being only of magnitude 5, and much distant from the pole point. 195 106 THE STARS. accuracy. The term "fixed stars" is so old and so universally used that I think it may be said to deceive nobody. Moreover, it is perfectly well known that certain objects which are often colloquially included under the name of "stars" are not fixed, but move with the earth in its orbit round the sun, which very word itself implies that they do not occupy fixed positions. Furthermore, precise modern observations, conducted with the most perfect instruments, have shown that the fact that a very considerable number of stars are ended with actual proper motion of their own, so that they move relatively to one another, and by amounts which are entirely beyond the grasp of the naked eye. The stars being of different apparent size, which for our present purpose means brilliancy, have been classified in magni- tudes, from 1 to 6, inclusive. But this classification is based on figures which one meets with in various astronomical publications - are very uncertain and fanciful. 1. The magnitude of a star is the degree of naked-eye vision ends with the 6th magnitude inclusive ; but with many persons the limit must be put at 5, whilst with a few other people it may be extended to 6. Thus within this range lie 7, 8, 9, io, 11, etc., all according as the observer's eyesight may or may not cease, though once often comes upon higher figures. All the recognised figures began with eye estimations in hygienic times. It was only when instruments were invented and used in such a way like way of estimating the brightness of a star, and, though organised photometric methods have often been proposed, they have only, up to the present time, been applied to a limited extent. The first catalogue at Harvard College, United States has published catalogues of naked-eye stars estimated in brightness by means of an instrument called a photometer; and the value of those labourious observations is immense. Independently of instrumental values of star-magnitudes, it Gr. ἀστρονομία, a wanderer. Gr. γῆς, light, and πλάνος, a measure. THE CLASSIFICATION OF STARS. 197 is customary to subdivide magnitudes decimally from o to 9, which gives us ten classes of stars assigned, which can only be regarded as, in many cases, a sham. When we come to deal with the stars in detail it will be seen that other classifications besides those depending on brilliancy have been proposed. These include the "variable stars," the temporary separate sections "coloured stars," "double stars," "temporary stars," "variable stars," and "moving stars." Next will follow, as a matter of course, the "multiple stars," clusters of stars, and nebula; and last, but not least, the Milky Way. But, before entering on such details, there are several other matters which must be brought under the notice of our readers. Posposing a consideration of the constellations to the chapter specially dedicated to them it will yet be convenient in this chapter to consider briefly the classification of stars. In early times, after a large number of the important constellations had been named (and the origin of most of these names is lost), it was found necessary to devise some means of distinguishing one star from another in the same constellation was urgently necessary. This was a matter taken in hand by the Arabian astronomers during the centuries following the fall of Constantinople. The names of stars now in use (Adelebanar, Altair, etc.) are of Arabic origin, with additions of Greek and Latin origin (Arcturus, Spica, Virgo). It is evident that this system is not very exact way, and for a certain time, but the need of more precise names was soon felt, hence Aldebaran came to be called Oculus Tauri, the "eye of the bull" a phrase supposed to give some indication. It requires no great amount of acuteness to realise that such methods to indicate stars as these were so rough and vague. In fact, it was not until about 1600 that any advance in the direction of scientific exactness was made in 1603 by a German astronomer named Bayer, in that 198 THE STARS. year published the first Celestial Atlas, the title of which was *Firmamentum, Omnium Astrorum continens Scheda- men et Notae*. In this work the order of the stars of each constellation were distinguished by having attached to them the letters of the Greek alphabet, and these have been used ever since, though they are not always used with the idea that he would label the stars in the order of brightness from a $\beta$ and so downwards as far as might be necessary till the alphabet was exhausted. The common idea is that the Greek alphabet is employed merely to represent the order of the stars so estimated; and occasionally it has been argued that the brightness of a star must have been considered before its position in the sky, and assigned brightness according to its position in the Greek alphabet. There is, however, no doubt that such an argument is worthless, and that the order assigned to the stars is founded further than to say that the brightest star in every constellation had a allotted to it, and perhaps the second brightest $\beta$, but that all the rest followed somewhat, but perhaps not altogether, after it. The next worker in this field was our own John Flamsteed, once Astronomer Royal. He prepared and in 1725 published his *Celestial Atlas*, in which he gave a list of all stars observed at Greenwich, and reduced to 1600, all the stars of which were numbered by his modern editor, Francis Bailey, from No. 1 onwards in each constellation. Flamsteed's numbers are given in Roman letters, and it will be seen that these Greek letters, as they are found engraved in almost every star- atlas in existence. When Bayer's letters are used they are usually prefixed by a capital letter $A$, $B$, $C$, etc., denoting a new stelation, thus : $u$ Ares Majoris, $b$ Canis Minoris, and so on. In addition to Bayer's Greek letters and Flamsteed's numbers there are a few stars indicated by Roman letters. Of these latter, but up to very limited extent, was really started before Bayer's time by an Italian, Piacentino di Siena, but SIR J. HERSCHEL ON THE STARS GENERALLY. 199 his use of them was limited. A long time elapsed after the invention of the telescope, and the commencement of methodical observations of stars as regards their exact places in the heavens, before the constellations and stars of the Southern Hemisphere were submitted to critical instrumental measure- ments. This did not come about till Lacaille published, in 1765, his Catalogue Astralum Stellarium, which contains 393 southern Stars, and 108 southern constellations. He placed himself in the Southern Hemisphere to himself, so to speak, and he turned his opportunities to account not only by observing its stars but also by making new discoveries. He thus created, at the same time creating 14 new southern constellations. In the particular case of the constellation Argo, one of vast extent and with many large stars, Lacaille got into a good deal of difficulty in deciding what name he should give for the 18o stars to which he deemed it desirable to attach letters. Thus it came about that, besides using up the Greek alphabets, he had to invent a new one, which he did by using cap and small letters, repeating indeed each several times, and so, of course, paving the way for a good deal of confusion. Sir John Herschel has written on the subject of stars, which are so very striking as to deserve questionation, the more so as they help to indicate the utilitarian side of astronomy, and moreover constitute what the French call politique de l'astronomie. It is this side which I take by the side Sir George Cornwall Lewis that astronomy is only a science of "pure curiosity." These are Sir John's words :- "The stars are the land-marks of the universe, and, amidst the multitude of objects which have been placed by its Creator as guides and records, not merely to elevate our minds by the contemplation of what is vast, but to teach us how we ought to live and how we ought to fear in His works. It is indeed hardly possible to ever appreciate their value in this point of view. Every well-determined star," 200 THE STARS. from the moment its place is registered, becomes to the astronomer, the geographer, the navigator, the surveyor, a point of reference, and is so far as possible kept the same for ever and in all places, of a delicacy so extreme as to require the most exacting attention. It is equally adapted for the most ordinary purposes; as available for regulating a town clock as for conducting a navy to the Indies; and it is also a useful instrument in the petty barony as for adjusting the boundaries of transatlantic empires. The stars are therefore carefully observed, and carefully recorded, the brazen circle on which that useful work was done may mouldler, the marble pillar torus on its base, and the brass sphere on its top, may be seen by posterity; but the record remains, and transfuses all its own excellence into every other branch of human labour. This work, giving to inferior instruments, nay, even to temporary contrivances, and to the observations of a few weeks or days, all the accuracy which originally at the cost of so much time, labour, and expense. As regards the number of the stars there is great mis- apprehension in the minds of many people. One's natural impulse is to exaggerate the numbers. Bearing in mind the difficulty of determining with certainty the limits of magnitude between the different magnitudes (the difference between the 1st and the 2nd not excepted), the following may be stated as approximately the numbers for the several magnitudes:
Magnitudes No. of Stars.
1st 65
2nd 65
3rd 45
4th 45
5th 3000
6th 3000
Below the 5th magnitude the uncertainties are too great to make exact estimates justifiable, and it is not safe to say more than that the visible stars, from the 1st magnitude down to the 9th inclusive, have been estimated by experienced observers STATISTICS OF THE STARS. 201 to be about 130,000 in number, though Argelander raised this figure to 250,000. It is generally considered that the total number of stars visible to the naked eye in England on any given night must not be put higher than 2500, whilst the grand total of all the stars in the heavens is supposed to be 100 million. All these humped together, may be said to be 130,000, as above shown though Heis, of Marburg, turned this into 30,000. Such statistics as these are not very profitable, because different observers have made different estimates by reason of taking a census of the stars on different principles: still, the subject could not be entirely passed over. A great many experiments have been made, though it can hardly be said to have been settled, on any sure basis, is the question whether the stars, or any of them, transmit any measurable quantity of heat. Experiments carried out many years ago at the Royal Observatory at Greenwich gave results which were decidedly affirmative answer, but when I quote one of the results in the form in which it was announced, scepticism on the subject will not be surprised. The following experiment was made with a telescope of 6 inches aperture and 2 feet focal length. The star Arcturus, at an altitude of $2^\circ$ above the horizon, was found to emit the same amount of heat as that which would be felt from a candle placed at a distance of 18 feet from the observer. An analogous difficulty—I had almost said impossibility—arose in connection with the question, What is the amount of light given out by the stars? All attempts to express this in figures secured me no success. It is true that I have heard some say more than that saying, that contriving a starless night with a night on which the stars are shining brightly, there is in the latter case a scarcity of light compared with the former case. Beyond this I do not deem it safe to particularise. Fabry, at Marseilles, published in 1910 the results of certain efforts made by him by way of developing previous attempts by Newcomb, Borda, and Vatican, a Dutchman, to determine the intrinsic brightness of the sky so far as starlight was 202 THE STARS. concerned. It need hardly be said that the task to be per- formed proved a very difficult one and the results very contradictory all round ; so much so that I hesitate to attempt to give any general account of them. But it is evident, by evi- dence, that the stars collectively do afford some light to the Earth. We must not pass away from the consideration of the stars as isolated or single objects without saying something on the interesting and time-honoured question of their twinkling. This optical phenomenon came before all of us in our earliest years. Who has not seen "Twinkle, twinkle, little star ; How I wonder what you are ! Up above the world so high, Like a diamond in the sky." This has been in part replaced by the advance of modern science, and accordingly we have the following revised version in circulation —— "Twinkle, twinkle, little star ; How I've feared you might be gone, When unto the midnight sky the spectroscope apply." Familiar as the phenomenon is to us, full scientific explanations of its nature and of its effects is evidently largely dependent upon the condition of the Earth's atmosphere, the varying influence of which undoubtedly affects the extent of the twinkling noticed on any given night. The weather indicates whether or not this is likely to be a night of excessive twinkling, which may indicate fine weather or the approach of weather of the contrary character ; but it seems quite certain that the presence (or absence) of clouds (which do not allow of starlight passing and devoid of rays) renders the approach of rain a certainty. Bright stars twinkle much more TWINKLING OF THE STARS. 203 than faint ones ; indeed, it may be said that faint stars do not twinkle at all. Again, stars low down near the horizon twinkle more than those high up in the heavens, and stars which are seen in a low-lying position on the Earth will notice the twinkling to be more marked than when they look at the same stars from a higher elevation. This is owing to the fact that the air in the surrounding country—in other words see the stars through a comparatively rarefied atmosphere. These facts accentuate the certainty that twinkling is a matter largely, one might say, dependent upon atmospheric conditions. It has been suggested, however, that this question of the density or rarefaction of the air, dependent on its state, is not the only cause (as is supposed) several of the principal fixed stars, presumably on account of the nature and peculiarity of their light, vary considerably in their display of twinkling. For instance, Procyon (a Canis Minoris) and Arcturus (b Bootes) twinkle much less, under all circumstances, than Vega (c Lyrae), a notable bluish-white star, which is very liable to twinkle. This star was exhaustively studied by the late C. Montagu, an amateur, who lived at Brussels, where I had many interesting conversations with him in 1878–80. He arrived at some very striking conclusions. He found that the twinkling was most frequent in winter and least in summer; and also more pronounced in winter than in summer. Dry weather in spring and autumn stands on about the same level as wet weather in winter; but in summer dry weather is much more marked than does spring wet weather. Variations in the barometer and in the humidity of the atmosphere, as indicated by the hygrometer, also affect the amount of twinkling. It is well developed when a rainy period likely to last two or three days is approaching; this merely before a 204 THE STARS. single casual rainy day; it also varies with the aggregate total rainfall, on a group of days, being greater as the rainfall is greater, and smaller and considerably decreasing directly the rain has passed away. Montgory's observations and conclusions were not based on careful, haphazard observations, but upon his own experiments with his own telescope, which he called a sextantometer, using the French word for twinkling as the basis of the name of his appliance. He found the number of scintillations (oncile), (twinkles) observed by him to vary from 30 to 60 per second in the dip of June to July to 97 in January and 102 in February, increasing or decreasing month by month in regular graduation. He also found that the number of scintillations increased with the sun's influence in increasing the twinkling. But this was not all in regard to his discoveries. It came into his head that perhaps the different classes of stars as classed by Secchi had respect to their twinkling, and he accordingly made some observations regarding to twinkling; and he was not disappointed. Anticipating here what belongs to a later part of this volume, a proper account of Secchi's classification will be given in a subsequent chapter. A series of some hundreds of observations of at bright stars belonging to Secchi's first 3 classes, was led to the following conclusion: The first class contains stars of about 80 scintillations per second, stars of the second class 69, and stars of the third class only 56. The more perfectly any star possesses the distinguishing characteristics of its class the more frequently does it twinkle; and this is exactly what is indicated by the above statement. This law may be stated thus: The more considerably the spectrum of a star is interrupted by dark lines, the more frequently does it twinkle. From which it follows that on the characteristic of each star depends its twinkling, both as regards its frequency and the colours which it displays. Secchi's has now been said by way of treating the stars as isolated objects in the heavens, and we must now proceed to DOUBLE STARS. 205 consider the stars in combination, beginning with pairs of stars, and leading up to clusters of resolvable stars, and finally to the recumdate matters as the "proper motions" of stars, "star-drift," and the "motion of the Solar System." The author has endeavored to include details not likely to interest the readers for whom this volume is primarily intended. DOUBLE STARS. A very large number of stars, including some of the largest and some of the smallest visible, though they appear to the naked eye, or through an open-lass or a small telescope, to be single stars, yet, with increasing power of magnification, are found that two of stars so close together as previously to have been regarded as only one star. Other stars seeming to be single are even more numerous than those which are on, four stars, or five stars, until the word "multiple" has to be used. We will start with the double stars, and then mention in numerous cases greatly increased optical assist- ance shows that one or other member of a pair, regarded only as a pair, is itself double again. Up to about 1830 only a few double stars were known. His powerful telescopes enabled him to convert 500 stars apparently single into double ones. The searches and perseverance of modern observers have resulted in the number of recognised double stars being increased to many thousands. The reader feels looking at a star and finding it in a small telescope no single, Fig. 260.—Two Stars at Different Distances as a Double Star. TWO STARS AT DIFFERENT DISTANCES AS A DOUBLE STAR. 206 THE STARS. whilst a larger telescope, or more power on the small one, reveals its nature though a thing interesting in itself, falls short of the grandeur of the discovery which many these objects after prolonged study of them. Herschel at first merely supposed that he was looking at 3 stars either stationary side by side at the same distance from the earth altogether different. The annexed diagram (Fig. 250) will make clear what is involved in this simple statement regarding a star, and how it is possible to have two stars so close together for circumstances to a discovery which both astonished and captivated him. In the early stages of his work as a double star hunter, he observed that the stars were not exactly equal distances with respect to the N. and S. points of the heavens, and their distances from one another. He continued observations of this character for the sole purpose of trying to discover whether observers might not find themselves subject to displacement of their stars being subject to displacement by way of parallax in consequence of the Earth's annual motion round the Sun. In order to understand this point it is necessary to apply as regards parallax, he found in a very large number of cases that these pairs of stars were experiencing relative change, and that their distances from each other varied in such a way as to indicate that they were joined by the centre of the two stars. In other words, he found that there were in existence systems consisting of 2 stars revolving about each other in elliptic orbits, and exhibiting all the phenomena connected with parallax. This discovery is of a twofold nature. First of all, there was the unforeseen and captivating novelty of it, and then there was the important fact that it showed that Newton's Universal Law of Gravitation was in operation far beyond the confines of the solar system to which it had been previously supposed to be limited. The actual application of the law to Herschel's discoveries did not take place till many years after those discoveries, when PLOTTING DOUBLE STARS MEASUREMENTS. 207 Savary, in 1830, computed an orbit for the star $\xi$ Ura Majoris which is now recognised as a binary, the smaller star of which steadily circulates round the larger one in a period of A diagram showing concentric circles with a central black circle. The outermost circle is labeled "Total Eclipses of the Sun". Fig. 261.--Diagram for sketching of the Corona in Total Eclipses of the Sun. Drawn by E. J. Stone, and available for plotting measurements at Dominion Stars. about 60 years. This work may be well commended to the notice of amateurs for the reason that both components are large, the larger one being of magnitude 4, and the smaller one 208 THE STARS. of magnitude 3½, and the distance between them generally being about 3° of arc, more or less. Herschel made his dis- covery known in a memoir which he presented to the Royal Society in 1802. The number of stars which, after about 25 years' study, he found to be ended with orbital motion was no doubt very considerable. But the labour of observation, time and labour has been bestowed on that class of star, and the assured binaries are now to be numbered by hundreds, not to say thousands, and the course of their motions is known in a complete short period of time—that is to say, there are not many stars whose periods are shorter than 60 years; but there are still many others whose periods are longer than 600 years, and therefore with many of these prolonged observa- tions, spread over a long expanse of years, will have to be carried out before we can hope to obtain any precise knowledge of the precise details thereof can be established. Herschel's discoveries were taken up and turned to account by F. G. W. Struve, who in 1873 published a great book containing means of 3112 double stars, and this work has been continued by many others; but the greatest living observer of double stars is undoubtedly the American astronomer S. W. Burhanum, whose name is connected with the discovery of the first binary star nowadays many fellow-labourers in various parts of the world. Burhanum's own experiences have for obvious reasons been somewhat restricted to the Northern Hemisphere with some difficulty owing to the destruction of the great observatory at Greenwich; but the great interest in the subject of double-star work is now proceeding at the Cape and in Australia. At the Cape the lead is being taken by R. T. A. Innes, who has already discovered several new doubles at Johannesburg, in the Transvaal; and, as time goes on, we may expect a large output of work from that centre. At the end of this volume a list will be given of some of the more interesting and easy double stars adapted for observation by small telescopes. Fig. 362 Plate XXXVII
1 2
3 4
5 6
COLOURED STARS. 1. ♗ Cassiopeia, yellow purple; 2. ♖ Andromeda, orange, green; 3. ♓ Piscium, pale green, blue; 4. ♔ Cassiopeia, pale green, white, brick red; 5. ♖ Boötes, pale orange, pale green. [API_EMPTY_RESPONSE] THE COLOURS OF STARS. 209 Many double stars exhibit the curious and beautiful pheno- menon of complementary colours. In such cases the larger star is usually more or less reddish or orange, and the smaller one bluish-green or greenish-blue. If complementary colours are observed in the two stars, the difference in their circum- size the circumstance may be attributed often to the effect of contrast. Perhaps it may be useful to put on record here a remarkable case of this kind, though an explanation of a digression, for the subject is one that belongs to the science of optics rather than to astronomy proper. Red is complementary to bluish-green. Orange is sky-blue. Yellow is violet-blue. Greenish-yellow is violet. The meaning of the foregoing table is this: that if any two colours which are complementary, as above, are put upon a rapidly revolving disc in proper proportions, when the disc is set in motion on its axis a composite tint, almost white, is exhibited. As regards this question of the colours of double stars, an examination made many years ago of the colours assigned, in Struve's catalogue, to 560 of his bright stars, yielded the following results: 387 pairs were of different colour and intensity; 101 pairs were of the same colour but of different intensity, whilst 120 pairs were of totally different colours. As regards the heavens, considered as doubles, an examination of the heavens will lead to its being noticed that single stars of a fiery red or deep orange hue are quite common; but those of a bluish-green or blue hue are very rare. In looking into the expressed opinions of observers who, under various circumstances, have made statements as to the colours of stars, it will be found that frequently great diversity exists—a diversity which is often inexplicable, and which it is A diagram showing a circle divided into four quadrants with labels indicating complementary colours. 14 210 THE STARS. hardly permissible to put down to actual changes of colour. Subject to this caution, the following stars may be named as coloured according to the colours prefixed —— White Stars—α Canis Majoris, a Leonis, β Leonis, a Lyrae, 5 Fucius Australis, a Ursa Minoris. Red Stars—β Canes Venatici, α Ursae Minoris, α Virginis. Blue Stars—α Auriga, β Orionis, γ Orionis, a Canis Minoris, Vulpeculae. Green Stars—α Aquila, a Cygni, Yellow Stars—α Bootis. The amateur observer will find it interesting to compare the statements made by him with those given with his own ideas on the subject as obtained by naked-eye observations; and I am far from saying that he will be able satisfactorily to confirm the accuracy of the statements made in the foregoing table. There is really only one way of testing the accuracy of these statements, viz., regarding the colours of stars, and that is, the enormous number which are dotted all over the heavens which exhibit various shades of blue and yellow. The blue stars are numerous, but the scale and yellowish at the other. An observer who sets himself the task of examining this matter for himself will probably be surprised at the immense number of stars to which he will have to apply his attention (and he will find that they are not all gradations). Thus we have been considering single stars and pairs of stars, but the study of sidereal astronomy does not by any means end here, because, when examining the heavens, we come across, as already indeed mentioned, triple, quadruple, and quintuple stars. These are not so numerous as might appear to be single, but which, with adequate optical assistance, are found to be compound, as these various designations imply. It is not, however, necessary to dwell on these stars, except in connection with what is known as "binary" stars. These are two or more stars which revolve round each other in such a manner that they appear to us as one star. They are distinguished from simple optical A diagram showing three stars revolving around each other. Plate 365 A star chart with various colored stars labeled. PLATE LXXXV 7. ♦ Bootes, orange, purple ; 8. ♗ Corona, white, blue ; 9. ♕ Norma, bright green, 10. ♖ Virgo, pale yellow, bright red ; 11. ♗ Cygnus, yellow, sapphire blue ; 12. ♖ Cassiopeia, pale green, bright blue. COLOURED STARS. [API_EMPTY_RESPONSE] VARIABLE STARS. 211 double stars, which are only double in appearance, there are certain triple stars which are subject to the complication that one of their components is variable. These are called "ternary" systems. Here we have either 2 stars revolving round one primary, or the 2 smaller stars of the trio revolving round the larger star. The first case is the more common, revolving round the 3rd, which is really the first, and needs to be called the primary star of the triple system. The possible complications to which such a condition of things brings us face to face with this problem I will content myself by inviting the reader to inspect the diagrams here given without pursuing the matter into further detail. VARIABLE STARS. Having discussed changes of colour in the stars, the question of changes of brightness naturally comes next, and opens up the subject which bears the recognised title of "variable stars." Supposing we take a star at random, and examine its peculiarities, we find long current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances, stars losing current but, save in one or two exceptional instances. This star is one of the most interesting of all the known variables; alike from the regularity with which it accomplishes its variations and from its great brilliancy when at maximum as observed by anybody. Its period is 331 days 8 h.; in other words it reaches its greatest brightness about 12 times 212 THE STARS. 11 years, when it sometimes attains the brilliancy of a star of the 2nd magnitude, at which brilliancy it remains stationary for about a fortnight, after which it diminishes during about 3 months, until it sinks down to a star of magnitude 9, or even becomes totally invisible. It remains in this condition for about 6 months, after which it begins to increase again, during next following 3 months, its maximum brilliancy. The foregoing periods and figures are only to be regarded as average ones, because there is strong evidence that the changes of brilliancy are not uniform but show a certain periodic change ; that is to say, that its maximum brilliancy is itself periodical, and that every eleventh maximum is marked by a special change of brilliancy. This fact has been shown to follow thus, whilst the average duration of the naked-eye visibility is about 18 weeks, in 1850-60 it was observed with the naked eye for about 21 weeks, whilst in 1868 it was seen only during 12 weeks. The variability of Alfa was first noticed in 1590 by D. Fabricius. The variable star Alfa is a very interesting one, and I think almost as much as Mira Ceti, is Algol (8 Persei), the variability of which stands second in point of date, for it seems to have been first recognised by Montanari in 1600, though it was not described till 1700. The variability of Alfa was first ascertained with some degree of certainty. This is generally stated in the following form : The normal brilliancy of the star is that of mag. 24. It varies between this minimum and its maximum for a period of about 23 minutes. It attains its minimum for about 20m., then in the course of 1h. 37m. it regains its normal maximum, and remains there for about 2h. 45m., after which it again sinks to its minimum for about 2d. 20h. 48m. The further study which has been given during recent years to the subject of variable stars has resulted in the discovery of many new ones, which vary through their changes in periods measured by a few days, and under physical circumstances akin to those which govern the
A graph showing light-curve variations. A graph showing light-curve variations.
Cepheid. Cepheid.
Fig. 264. Fig. 265.
A graph showing light-curve variations. A graph showing light-curve variations.
D. S. P. R. D. S. P. R.
57th Division - 3-8 57th Division - 3-8
Fig. 266. Fig. 267.
Mean Light-curves of certain Variable Stars.
214 THE STARS. changes of Aqol ; and accordingly we now speak of certain stars as " stars of the Algol type," and by way of explanation it has been suggested that non-luminous satellites revolve round the primary star and eclipses it at stated intervals. Another variable star of great interest, which, like Algol, is very much alike to Algol in its period, is Beta Cephei, also one of Goodricke's stars, and recognised by him in 1784 to be a variable. Counting from minimum to minimum, its period is 5.4 days. The interval between maximum and maximum is unequally divided as regards the minimum stage, for the time occupied in descending from maximum to minimum is greater than the time occupied in rising from minimum to maximum. The intervals are 3.4 d., 1.9 d., and 1.4 d., respectively. It is remarkable how little variation there is in the sequence of its changes from those which have just been described, for it has a double maximum and minimum within what is now recognised to be its complete period of 5.4 d. It is probable that this periodicity was discovered through the variability of this star in 1784, and induced him to assign to it a period of only half the true complete period as just mentioned. The change from maximum to minimum takes place in 2.6 d., the star descends to its first minimum of mag. 4 ; then it rises to maximum again, and descends to a second minimum, but at this second minimum it is brighter than at the first, being mag. 3.4 instead of mag. 3.6. It is easy to see how it came about that Goodricke was misled into fixing the period at one-half its true amount. Anglender asserted that the period itself, taken as 5.4 d., was too long, and he found that when he made that remark in 1860, I do not find any recent observations which throw doubt on his conclusion. The Algols all belong to the Northern Hemisphere, but the Southern Hemisphere has in Ω Argus a once-naked-
T Ushba Majoris
1/2 - 5/6 = 13/2		 S Ushba Majoris
1/2 - 7/8 = 13/16
Fig. 288. Fig. 289.
8 Boorm
1/4 - 7/8 = 13/4		 B Camelopardalis
1/4 - 7/8 = 13/16
Fig. 270. Fig. 271.
Mean Light-curves of certain Variable Stars. 213 216 THE STARS. eye variable, the uncertainties of which have puzzled several generations of astronomers. Its magnitude during the past 150 years has been noted as 4, 2, 1, 2, 1, 2, 3, 4, 5, 6, 7, 7½, 8, and even 9. It was first observed by Bessel in 1886, and since then y seems to have further gone down to mag. 8, where it was in 1907, and probably is still. All that we can say about its future is that it will continue to be variable until some preparatory to a great descent so as to become invisible to the naked eye. Schönfeld summarily settled the question of period by saying that ξ Argus has no regular period; and there is no reason why this should be true. The same view accords in substance with the opinion of Sir J. Herschel, expressed at an earlier date, that this is a star "finitely variable to the naked eye," but that its variations have not occurred over centuries, apparently in no settled period, and show no regularity of progression. There are many stars dealing with notable naked-eye stars, and there are a few others of that sort which can hardly be called notable. When, however, we resort to the telescope and direct our attention to telescopic variable stars an enormous number of them appear to us as being infinitely variable to those who possess good eyes, patience, and telescopes of adequate power. It would be monotonous and somewhat boring to enumerate all these stars; but the diagrams here given will convey some idea of the changes which they undergo and the delicate character of the observations required before safe conclusions can be arrived at. It is customary with astronomers, when they wish to indicate in the most easily appreciated form variations in various stars, to represent them on a diagram in which ordinates are represented by the ordinates and abscissae of curves. This brings the changes much more readily home to a reader than mere tables of figures. Figs. 264 to 275, record the changes which were noted to have taken place in certain well-known Diagrams. **Fig. 272.** **Fig. 273.** **Fig. 274.** Mean Light-curves of certain Variable Stars. **Fig. 275.** 117 218 THE STARS. variable stars at the dates stated, whilst Fig. 276 records the fluctuations in the temporary star Novi Persei between February and April 1901 as recorded at Oxford by Mr. A. A. Rambaut, the Radcliffe observer. TEMPORARY STARS. A branch of sidereal astronomy which has much of the sensational interest is that which is covered by the title "Temporary Stars." At many epochs of history the stars have suddenly burst forth in the heavens, and shown as bright stars for limited periods of time, stars which probably ought to have been visible for ages. The records of these stars, as recorded by old monastic and other writers undoubtedly were only mere luminous meteors, or fireballs, and a few of them continued up from one night to another. The contemporary records of stars suddenly becoming visible in places where no stars had been seen before, and which remained visible for weeks or months before their final disappearance. The cases are very numerous, but they are all of a short duration, and their brilliancy to become conspicuous, for it has been more common for a conspicuous star to appear suddenly in a place where no star had previously seen, and then at once to begin a downward career. It will be prudent, if we desire to take our stand on the firm ground of fact, not to go too far back in seeking for instances of temporary stars. The case of the star Arcturus is the most ancient which I desire to put forward. He has left us a full account of it, a substance of which is that it was first seen in 1572, and that it was not visible again for 17 months, or till March 1754. At its best it was brighter than Sirius, and rivalled Venus. Tycho Brahe, having no telescope, of course lost the star as soon as it descended below the 6th magnitude, and nobody seems to have seriously attempted to look into the matter until P. Arvesz in 1894, pub- A diagram showing fluctuations in the temporary star Novi Persei between February and April 1901. TEMPORARY STARS. 219 lished a map of an area in Cassiopeia which was supposed to include the place of Tycho's star. Anglender, having assigned a position to the star, pointed out that its light was decidedly variable, and Hind and Plummer followed this up in 1873 by stating that this little star was variable. There the matter remains, no one apparently having attempted to follow it up after. The exact position of Tycho's
Feb. Mar. Apr. May Jun Jul Aug. Sep. Oct. Nov. Dec.
-15 -10 -5 0 5 10 15 20 25 30 35
FEB. MARCH. APRIL. MAY. JUNE. JULY. AUGUST. SEPTEMBER. OCTOBER. NOVEMBER. DECEMBER.
-15 -10 -5 0 5 10 15 20 25 30 35
Fig. 276.--Light Changes in Nova Persei, 1901. star, as given by Anglender, brought up for precession to January 1, 1913, is as follows:
R.A. - h m s s Declination - d' d' d' N.
The reason that some attention was given to the subject in 1873 was that the theory was current that Tycho's star was a
Description: A graph showing light changes in Nova Persei from February to December, with values ranging from -15 to +60. The x-axis represents months (FEB., MARCH., APRIL., MAY., JUNE., JULY., AUGUST., SEPTEMBER., OCTOBER., NOVEMBER., DECEMBER.) and the y-axis shows light changes in units (e.g., -15, -10, -5, etc.). The graph shows a general downward trend from February to December, with some fluctuations within each month. The highest value is around +60 in December, and the lowest is around -15 in February. The overall trend suggests a decrease in light over time. Description: A table showing the light changes in Nova Persei from February to December, with values ranging from -15 to +60. The x-axis represents months (FEB., MARCH., APRIL., MAY., JUNE., JULY., AUGUST., SEPTEMBER., OCTOBER., NOVEMBER., DECEMBER.) and the y-axis shows light changes in units (e.g., -15, -10, -5, etc.). The graph shows a general downward trend from February to December, with some fluctuations within each month. The highest value is around +60 in December, and the lowest is around -15 in February. The overall trend suggests a decrease in light over time. Description: A table showing the light changes in Nova Persei from February to December, with values ranging from -15 to +60. The x-axis represents months (FEB., MARCH., APRIL., MAY., JUNE., JULY., AUGUST., SEPTEMBER., OCTOBER., NOVEMBER., DECEMBER.) and the y-axis shows light changes in units (e.g., -15, -10, -5, etc.). The graph shows a general downward trend from February to December, with some fluctuations within each month. The highest value is around +60 in December, and the lowest is around -15 in February. The overall trend suggests a decrease in light over time. Description: A table showing the light changes in Nova Persei from February to December, with values ranging from -15 to +60. The x-axis represents months (FEB., MARCH., APRIL., MAY., JUNE., JULY., AUGUST., SEPTEMBER., OCTOBER., NOVEMBER., DECEMBER.) and the y-axis shows light changes in units (e.g., -15, -10, -5, etc.). The graph shows a general downward trend from February to December, with some fluctuations within each month. The highest value is around +60 in December, and the lowest is around -15 in February. The overall trend suggests a decrease in light over time. Description: A table showing the light changes in Nova Persei from February to December, with values ranging from -15 to +60. The x-axis represents months (FEB., MARCH., APRIL., MAY., JUNE., JULY., AUGUST., SEPTEMBER., OCTOBER., NOVEMBER., DECEMBER.) and the y-axis shows light changes in units (e.g., -15, -10, -5, etc.). The graph shows a general downward trend from February to December, with some fluctuations within each month. The highest value is around +60 in December, and the lowest is around -15 in February. The overall trend suggests a decrease in light over time. Description: A table showing the light changes in Nova Persei from February to December, with values ranging from -15 to +60. The x-axis represents months (FEB., MARCH., APRIL., MAY., JUNE., JULY., AUGUST., SEPTEMBER., OCTOBER., NOVEMBER., DECEMBER.) and the y-axis shows light changes in units (e.g., -15, -10, -5, etc.). The graph shows a general downward trend from February to December, with some fluctuations within each month. The highest value is around +60 in December, and the lowest is around -15 in February. The overall trend suggests a decrease in light over time. Description: A table showing the light changes in Nova Persei from February to December, with values ranging from -15 to +60. The x-axis represents months (FEB., MARCH., APRIL., MAY., JUNE., JULY., AUGUST., SEPTEMBER., OCTOBER., NOVEMBER., DECEMBER.) and the y-axis shows light changes in units (e.g., -15, -10, -5, etc.). The graph shows a general downward trend from February to December, with some fluctuations within each month. The highest value is around +60 in December, and the lowest is around -15 in February. The overall trend suggests a decrease in light over time. Description: A table showing the light changes in Nova Persei from February to December, with values ranging from -15 to +60. The x-axis represents months (FEB., MARCH., APRIL., MAY., JUNE., JULY., AUGUST., SEPTEMBER., OCTOBER., NOVEMBER., DECEMBER.) and the y-axis shows light changes in units (e.g., -15, -10, -5, etc.). The graph shows a general downward trend from February to December, with some fluctuations within each month. The highest value is around +60 in December, and the lowest is around -15 in February. The overall trend suggests a decrease in light over time. Description: A table showing the light changes in Nova Persei from February to December, with values ranging from -15 to +60. The x-axis represents months (FEB., 220 JUNE., JULY., AUGUST., SEPTEMBER., OCTOBER., NOVEMBER., DECEMBER.) and the y-axis shows light changes in units (e.g., -15, -10, -5, etc.). The highest value is around +60 in December, and the lowest is around -15 in February. The overall trend suggests a decrease in light over time. The reason that some attention was given to the subject in 1873 was that the theory was current that Tycho's star was a 220 THE STARS. reappearance of objects alleged to have been temporary stars, and visible in 943 1254 ; so that these objects had been temporary stars themselves. It is possible (very slight) that Tycho's star was the reappearance of a variable star whose period was 300 years, more or less. But all this would seem to be an idle hypothesis, and we have no other reason whatever for suspecting that Tycho's star was to reappear after the lapse of three centuries. The year 1004 was marked by the appearance of a temporary star in the constellation Ophiuchus, which became nearly as bright as Venus, and lasted a year or more. Kepler wrote a book about it which has come down to us. In 1867 appeared two new stars, which rose to the brightness of a star of the 3rd magnitude, and lasted two years from first to last, during which period it more than once increased in brightness, and then diminished, before it finally disappeared. A long interval elapsed before we had another new star. On April 28, 1848, a fifth-magnitude star was seen by Find in Ophiuchus, which rose to the 10th magnitude on the 2nd of May, and then descended to the 11th or 12th magnitude, at which it may or may not stay. May 1849 saw a new star, which created a considerable sensation because of the sudden outburst which characterised it. As a star of mag. 93 it was recorded by Angelerde in 1851 at Toulouse, at Ham in England, on May 12, 1860, as a very bright star. In view of the negative testimony of Schimizzi, of Athens, with the positive testimony of Birmingham, it would seem that this star suddenly rose from the 13th to the 10th magnitude on the evening on which Birmingham saw it. It soon began to fade away, and by the end of the month had fallen to mag. 9. It continued at this magnitude until the following September when it rose to 74 in Sibiu and was nearly stationary in brightness for the remainder of the year. QVADRANS MVRALIS SIVE TICHONICUS. A detailed illustration of Tycho Brahe's Mural Quadrant for measuring Vertical Angles. The quadrant is shown in various positions, with a man pointing to different parts of the instrument. The top section shows a celestial globe, while the middle sections depict astronomical instruments and diagrams. The bottom section shows a table with books and papers, and a man working on the quadrant. Fig. 277.--Tycho Brahe's Mural Quadrant for measuring Vertical Angles. 221 222 THE STARS. This star is now permanently put upon the list of variable stars under the designation of T Coronae; but it seems to have been ignored by variable-star observers during recent years. On November 24, 1876, Schmidt, at Athens, observed a new star of the 3rd magnitude in Cygnus, yellowish in colour. By the end of December it had descended to the 7th magnitude, and afterwards became still smaller. The last recorded observation was made on January 10, 1877, when it was dim on September 2, 1877, when the spectrum was reduced to a single line, the continuous spectrum and all the other lines having disappeared. August 1853 saw the outburst in the constellation Andromeda of a new star, which created at the time a great deal of excitement. This excitement was largely due to the position of the new star near the centre of the nebula, and it may be said that the appearance of standing out sensibly in front of the nebula. When first seen, which appears to have been on August 23, or a few days after, it was of about the same magnitude as the sun. It never got beyond that, and rapidly began to decline until it reached about the 11th magnitude, and then it became visually lost in the nebula, though from first to last the impression continued that it was standing out sensibly in front of it, so that it had nothing to do with the nebula itself. Later in the same year, on December 17, J. E. C. found a new star of about the same magnitude as before mentioned from mag. 6 to mag. 9, or less, and then disappeared, and afterwards again came into view, and is now permanently enshrouded in the nebula. This star has given rise to a sudden increase of light in the month in which it was first found. It is now known as U Orionis. Early in 1852 a new star appeared in the constellation Auriga, which was discovered by Bessel, whose results are highly interesting. The fact of the star's existence was communicated to Copeland, Director of the Observatory of Edinburgh, A star chart showing a new star in Auriga. NEW STARS. 223 by means of an anonymous postcard, which led him at once to search for and find the star, which he was told was of the 5th magnitude. The authorship of the postcard was after- wards avowed by a certain Dr. Anderson, who found the star by means of his telescope. Klein's Star Atlas, used in conjunction with a small pocket-telescope. When news of the discovery was conveyed to the other side of the Atlantic, Professor Pickering, of Harvard College Observatory, immediately set out to have it taken photo- graphed by his 13 times between December 10, 1891, and January 20, 1892. He considered that his plates took all stars of the 6th magnitude or brighter. It is probable that it will appear on the plate of December 5, it must have brightened up between December 6 and December 10. The new star, henceforth known as Nov. 17, appeared on November 17th, and on February 26th, when it rapidly diminished and on April 26 was no more than of the 16th magnitude. Later on in the summer it brightened up to about the 10th magnitude. In 1901 a new star appeared in Perseus, which lasted a long time, and underwent various and noteworthy changes. There seems to be some doubt whether this star is real or not. It seems to have had several independent discoveries on Febru- ary 22, but the first public announcement was made by Dr. Anderson of Edinburgh, the discoverer of New Auriga (see page 20). This star was discovered by Mr. H. A. Huggins at Harvard Observatory on February 22nd, and by Mr. J. H. Schreiber at Kiel on February 23rd, both being independent discoveries made on the same night. February 21st at Kiel, in Russia, by a boy 16 years of age named Borisnok. When Borisnok saw the star he thought it was a comet, but when he looked again it had disappeared; and when he looked again it had reappeared; and so forth until Borisnok, perhaps erroneously, called it r.j.. The evidence as to its history seems to show that on February 20 the star had not become visible. After February 22 it became very faint indeed, and remained so for several days or for day or two, and by March 18 had descended to the 4th magni- tude, which in June had become the 6th magnitude, and at the 224 THE STARS. end of the year the 7th. These changes were not regular, because its brilliancy oscillated several times. The final history of this Nova was very remarkable, because it seems to have either turned into a nebula, or, in some mysterious way, to have disappeared. I give the details as to this would occupy too much space for these pages. Other new stars of recent date are the following : *Nova* Lalande's, which appeared on the 10th of July, 1810 ; T. E. Apian ; *Nova Sagittarii*, discovered photograpically in September 1899 at Arequipa, in Peru, but the fact not known till an examination of the plates in 1911 ; *Nova Geminorum*, discovered by Sir William Parsons in 1863, and observed in the same way. It showed spectroscopically the characteristic hydrogen bands, accompanied by dark bands on the side towards the violet. Professor E. C. Pickering, in 1881, proposed the following classification to link together all the stars which come under the designation of " temporary " or " variable " stars : 1. Stars of class 1, which appeared in the year of a eclipse of Saturn in 1752 ; new star in Corona 1860. 2. Stars undergoing great variations in light in periods of several months or years. Examples : a Ceti, and a Cygni. 3. Stars undergoing slight changes according to laws as yet unknown. Examples : a Orionis and a Cassiopeia. The light of this star is continually varying, but the changes repeat with great regularity, and do not exceed one or two days. Examples : b Lyrae and c Cephei. 5. Stars which every few days undergo a few hours a reversal of their brilliancy, and then return to normal brightness with great regularity. Examples : b Persei and c Cancri. In the case of stars belonging to class 5, the observed variation could be very satisfactorily explained by the theory that the reduction in light is caused by a dark eclipsing satellite. The foregoing accounts of recent new stars will suffice to OPENINGS FOR WORK. 225 give the reader a general idea of what these objects are, and I hope to bring it home to the reader also, to understand that, if they choose to avail themselves of opportunities which from time to time occur, they may often be able to render useful service to science, and, at the same time, to earn some credit and distinction for themselves. A page from a book with text and a small illustration of a person in a suit. 15 CHAPTER XII. GROUPS OF STARS AND NEBULÆ. Stars in groups classified.—Irregular groups—Clusters of stars more or less compressed and symmetrical—Planetary nebulae—Elliptic nebulae—Spiral nebulae—Planetary nebulae.—Nebulae of the Milky Way—Distribution of nebulae and clusters over the heavens—The Milky Way—Brief description of its position.—Its historic names. Having started in the previous chapter with single stars and gradually got up to multiple stars—which phrase may be said to mean, say, half a dozen stars—and then to groups of stars which are to be met with in the heavens in great numbers and embracing all gradations of quantity from a few dozen up to literally myriads, according to the size of the field of view considered—the variety of these groups to be found in the heavens is very great, both as regards the number of the stars composing them and their relative positions. It will be convenient here to conveniently consider the objects now to be described under three general heads, the third of which will need special subdivision by itself. The three main divisions may be as follows: (1) Irregular groups, many of them visible to the naked eye. (2) Clusters of stars more or less compressed and symmetrical. *pedes* ten thousand, also *counseles.* not Fig. 278 PLATE LXXXVI. A circular image showing a cluster of stars, identified as the Pleiades (Temptel), with the Nebula near Menope. The Pleiades (Temptel). With the Nebula near Menope. 206 Fig. 279 PLATE LXXXVII. Nebula in the Pleiades, Dec. 8, 1888 (Isaac Roberts). 247 CLASSIFICATION OF CLUSTERS AND NEBULAE. 227 metrical, and resolvable into separate stars with adequate optical assistance. (3) Nebulae for the most part irresolvable, however powerful may be the telescopes which are brought to bear on them. The third class may be subdivided as follows, the sub- divisions having regard chiefly to differences of shape. (i) Elliptic nebula. (ii) Spiral nebula. (iii) Planetary nebula. (iv) Large nebula of irregular form. The foregoing classifications may be considered as compe- tently representing the clusters and nebulae; but the reader must be warned beforehand that only a few objects in some of the classes, and none in the other classes are at all within the reach of ordinary small telescopes which the readers of this work are supposed to possess. Many of the objects in class (i) are more or less non-teles- copical, so to speak; that is to say, are too large and scattered to be seen by any telescope other than a low-power open-glass with a very large field. The Pleiades and Hyades, both in Taurus, are undoubtedly the most conspicuous objects in the sky, and they have been, historically the first mention of them begins with Homer. The tradition is well known, and as old as Ovid, that there were originally 7, but that one had fallen out of sight. The origin of this story is unknown, and it would seem that one ought to say that the tradition is scientifically untrue, because, not only can 7 still be counted, but a good many more. This is not surprising when we consider that in ordinary cases, whilst ordinary eyes often do not get beyond six in the counting, good eyes and extra good eyes can get up to 8, 10, or even 12. A proof that there is nothing magical in the number 7 is found in the fact that 9 of the stars have for 228 GROUPS OF STARS AND NEBULE unnumbered centuries borne specific names, which, with their magnitudes, are as great as the brightest is known as Alcyone (alpha V of the Taurus magnitude ; next to it is Aldebaran, the eye of the Bull). Merope and Taegeta 43, whilst Celeno, Asterope, and Pleione are all much about the same size, say mag. 6. But besides these more or less conspicuous members of the group, there are others which are only revealed in the telescope. There is a matter connected with the Pleiades which is most mysterious. In 1859 a well-known astronomer, Tempe, discovered that he could see what he thought was a telescopic comet ; but it was after wards found to be a nebula and not to be moving, it was clear that it was not a comet, but a nebula which had suddenly moved into his field of vision. It was not until 1870 that the subject it became certain, not only that Tempe had observed a genuine nebula, but that nebulous matter was to be regarded as a real body in space. The stars of the Pleiades are the chief stars (Alcyone, Electra, Mira, Merope, and Celeno) being involved in nebulosity. It seems certain that this nebulous matter has only come into view during the past hundred years, but it is impossible hereafter to know its exact nature. The Hindoo call the Pleiades "The Hinds and Chickens." The Arabs call them "The Seven Sisters." In Ibn Quatze Sanpo Panza describes his fancied ride through space, saying: "We happened to travel through the region of the Pleiades and saw the seven Don adas : It was possible for us to reach that part where we are the Fleiades, or the seven goats, as Sanpo calls them." The Hyades constitute a group of stars altogether inferior to the Pleiades in brilliancy and size. They are scattered about but because they are much scattered. Still, they must be treated as being a group, and they have been recognised as such for many centuries. In the constellation Cancer we have another historic group Fig. 280 PLATE LXXXVIII. The Cluster 13 M. Herculis (W. E. Wilson). Fig. 281 PLATE LXXXIX. Constant. [29] CONSPICUOUS CLUSTERS 229 known as Pegasus, which makes a very effective show in a telescope of large field and low power. This object is some- times met with in old maps, but it is not mentioned by the "Be-e-hive," but that name, as well as its Latin name, is lost in antiquity. Fully 2000 years ago it was recorded by two Greek astronomers, who called it "The Coma." In the course of time, being that, under such prospect, the group lost its sharp stellar appearance and became misty. The Coma Berenices is made up of a number of stars which, though it may be named in connec- tion with the three preceding groups, has its constituent stars too scattered to be quite fairly comparable with them. Of these stars, however, only a few are included under the second of the main heads already specified, namely, Clusters of Stars. These are of various sizes and shapes, and they are all so faint that they appear as nebulae and nothing else, but in some cases even a small amount of additional optical power renders it easy to see that the seemingly nebulous mass is really composed of several stars. The main number of the objects belonging to the class which we are now considering are specially labelled "Globalular Clusters." They have received this name because they are so numerous that they form a sort of globular cluster, though the causes which gave them this form and keep them retaining it are unknown. The most striking object of this class is the Great Cluster in Hercules, also known as M. Herculis for which the Southern Hemisphere provides a magnificent counterpart in the clusters surrounding the Stars Centauri and 47 Tucanae of Centauri and 47 Tucanae. The reason for the cluster in Hercules, just named, deserves explanation. It stands for the initial of the surname of a famous French astronomer, Messier, who earned the name of founder by cataloguing nearly a century and a half ago, all the objects he was able to observe in his telescope with an aperture of only 2 inches 230 GROUPS OF STARS AND NEBULE. With such a telescope he was naturally unable to realise very distinctly the difference between the objects which are now called Nebulae and Stars. He therefore grouped them all together under the comprehensive title 'Nebuloses and Masses of Stars.' His labours, notwithstanding that his opportunities were so limited, have been most valuable, so far as this whenever we come across a cluster or nebula in Messier's number and letter prefixed to it, we know at once that it can be seen with a small telescope, however imperfectly. Nevertheless, Messier's catalogue is not altogether sufficient massa. Sir J. Herschel saw signs of its stars forming curved lines, which feature Lord Rosse interpreted as indicating a spiral structure. The same applies to the 47 Tucani, and therefore cannot speak of them from personal knowledge ; but, judging by the language used by those who have seen them, they must be magnificent objects, surpassing the best of the Comets. The 47 Tucani is 'undoubtedly the finest in the sky,' and the 47 Toucani as second only to the Centauri. Neither of these two objects, which are visible in England seems to come I M. Liburn, very accurately described by Webb as a 'beautiful assembly of minute stars greatly compressed in the centre,' is not visible in England. In fact, though it is said that it has 'out-liners in all directions and a bright central blaze.' Messier committed himself to an opinion respecting this cluster which would seem to be correct. It is difficult to see how these objects vary much in appearance, according to the size of the telescope employed in viewing them. We shall see presently that this is not always true when we consider respecting 5 M. Liburn should be posted up as a caution to men of science. "He assured himself that it did not contain a single star." Other clusters of the type of those which have gone before will be found amongst list in the Appendix.
1 Nebulose of the Pleiades.
2 Nebulose of Orion.
3 Nebulose of Perseus.
4 Nebulose of Andromeda.
5 Nebulose of Coma Berenices.
6 Nebulose of Hercules.
7 Nebulose of Lyra.
8 Nebulose of Cygnus.
9 Nebulose of Cassiopeia.
10 Nebulose of Ursa Minor.
11 Nebulose of Ursa Major.
12 Nebulose of Bootes.
13 Nebulose of Canes Venatici.
14 Nebulose of Pegasus.
15 Nebulose of Aquarius.
16 Nebulose of Pisces.
17 Nebulose of Aries.
18 Nebulose of Taurus.
19 Nebulose of Auriga.
20 Nebulose of Gemini.
21 Nebulose of Cancer.
22 Nebulose of Leo.
23 Nebulose of Virgo.
24 Nebulose of Libra.
25 Nebulose of Scorpio.
26 Nebulose of Sagittarius.
27 Nebulose of Capricornus.
Messier's Catalogue:
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Fio. 283 PLATE XC. A black and white photograph of a cluster of stars against a dark background. 47 Tournai. 290 Figs. 283-285 PLATE XCI. A star cluster with a central bright core and a surrounding halo of fainter stars. 2 M. Aquaril. 5 M. Libra. (Sir J. Herschel.) A star cluster with a large number of stars spread out in a circular pattern. 2 M. Aquaril (Earl of Rosse). This picture shows how a large telescope opens out the stars which are very close together into separate points of light. The stars in this cluster are so close together that they appear to be one star when seen through a small telescope. When viewed through a large telescope, however, each star can be distinguished as a separate point of light. 131 **REMARKABLE CLUSTERS.** 231 Respecting one of these globular clusters, 80 M. Scorpii, a singular circumstance is no record. In 1860 a well-known observer, Poggendorff, published a paper on the stars of the heavens which should have included the cluster, found that it had disappeared, and that its 7-magnitude star was occupying its place. A fortnight later this star had returned and the cluster was once more presenting its normal appearance. These changes were also noticed by two German observers, and therefore there can be no doubt about their reality. It seems probable that some change has taken place in the cluster, and the conclusion is therefore inevitable that the star was a temporary one, quite independent of the cluster, and that it appeared in front of it and lasted a very few days, and had then disappeared without leaving any trace of some unknown cause or causes. Of clusters, not globular but large and attractive, 67 M. Cygni is worthy of notice. By far the most striking and beautiful of the loose and irregular clusters in the heavens, probably that which surrounds the star A Crucis is the most remarkable. Sir William Herschel, in his following years, observed this cluster and described it as one of the most beautiful of its class. Some 40 years later, Russell, at the Sydney Observatory, made observations on it, and found that many of them in the 40 years' interval had moved from Herschel's position, and in consequence (it was to be assumed) of their being ended with a different magnitude. The following is his account: "The colours of this cluster are very beautiful, and fully justify Herschel's remark that it looks like a 'superb piece of art.'" We will now pass on to the nebulae, properly so-called, the number of which has been greatly augmented of recent years. Sir W. Herschel developed Messier's catalogue of 103 objects into hundreds, which Sir John Herschel's labours at the Cape and elsewhere brought up to thousands. In 1864 he published 232 GROUPS OF STARS AND NEBULE. a complete general catalogue of all those then known, which numbered 5097 objects. This catalogue seems to have stimulated the development of this branch of sidereal astronomy, and has been revised, corrected and enlarged, the new edition comprised 7840 objects; and this number has since been largely increased by the discovery of many more. It is an incidental result of searches for new comets and double stars. It should be clearly stated that, for the profitable examination of nebulae of all kinds, large telescopes are indispensable, and that the results obtained with even the largest view will not give satisfaction in small ones is very limited ; but, in order to present a complete survey of these objects, according to the classification given in the catalogue, it was necessary to include within its limits a certain number which are hopefully beyond the reach of small telescope. Of the 7840 objects in the heavens afford only a few examples—scarcely a dozen in all. The most remarkable is G. M. Lynne, situated about midway between β and Λ, and the only annular nebula within reach of a telescope of moderate power. Sir William Herschel describes it as "a bright star on a flat, oval, solid ring with the central vacuity not quite dark, out." filled in with faint nebula like a gauze stretched over a bow. In 1860, Huggins, Bessel, and Secchi all claimed to have resolved this object into two stars. Sir William Huggins asserts that it was wholly gaseous. This question of nebulae seems to me one of great difficulty and complexity, and I must confess myself not to be satisfied with many of the claims put forward based on spectroscopic observations. It is true that at various degrees of eccentricity are not uncommon, but there is only one conspicuous large one, namely, If I do not make use anywhere of the phrase "white nebula," which some writers have recently tended to substitute it, it becomes I think it an unneces- ary and illogical phrase. Practically all nebulae are "white" Fig. 286 PLATE XCII. The Clusters 33 and 34 of VI. Persei (A. A. Rambaut, Redcliffe Observatory, Oxford). 23] Fig. 287 PLATE XCHII The Great Nebula in Andromeda (H. J. Shepstone). 1365 Figs. 288-289 PLATE XCIV. The Spiral Nebula S 1 M. Canum Venaticorum. (S. J. Hubble) 030 Plate XCV. Pro. 250 Spiral Nebula in Ursa Major (H. J. Shepstone). [33] Spiral Nebula. 233 the "Great Nebula in Andromeda" (x M.). Its elliptic outline is shown in a small telescope, and the nebula is sufficiently large to be seen with the naked eye. The most important instru- ments of great size are required to show the curious details of rifts or black streaks which run nearly parallel to the major axis of the oval on the S, side. Taken as a whole, the nebula must be regarded as a spiral system, but its structure is very irregular, and a considerable number of isolated stars are to be found within its limits. There is no other elliptic nebula within the reach of any telescope, and it is only by means of such an instrument that one can point out that there are several which have double stars at or near each end of the ellipses, which in these cases is very elongated compared with its breadth. The first known example of a nebula known as "Spiral" or "Whirlpool" nebula was first made known by the 3rd Earl of Worcester when he brought his great reflectors from Panserton to look at the heavens. He was so struck by this object that he drew whose structure was discovered by him are well known because they have been engraved in a great number of books ; but the observations and researches of recent years, especially those of Lord Rosse, have shown that there are many more masses of nebulous matter, and indeed aggregations of stars generally assuming a spiral form, are much more common than was formerly supposed. Lord Rosse brought to an end his own discoveries in this field. The two most important spiral nebulae, determined to be such by Sir Norman Lockyer, are known as x M. Canum Venaticorum, and ng 91 Virgo. These are both very large objects, and their proper able degree, not only the changes which take place in the appearance of clusters and nebulae according as they are viewed through telescopes of different sizes, but also the results of jump- ing at conclusions and using dogmatic language in dealing with these matters. Figs. 288 and 289 represent this nebula as drawn by Admiral Smyth, Sir J. Herschel and Lord Rosse respectively, whilst Fig. 290 supplies a photographic view. 234 GROUPS OF STARS AND NEEULE. Except for the direct evidence of the fact which is available, it would be difficult for any chance spectator to suppose that all these nebulae are really in motion. The case of the nebulae at 09 M. Virginis, the spiral form may be said to be so obscurely visible in Lord Rosse's sketch, as not to need even a moment's argument to show that they are stationary. This is a very important question. What meaning is to be attached to the spiral formation in the heavens which are here brought under notice? I must frankly admit that I am not prepared with an answer to this question; but I have no doubt that the great majority of astronomers will find that an American observer, Holden, speaking of a planetary nebula (presumably to be presented), says that it "is apparently composed of a number of stars arranged in a spiral form." It is hard to resist the conviction that these are arranged in space in the form of a true helix"—another way of expressing the idea of a spiral nebula. The term "planetary" was applied by Sir W. Herschel to certain nebulae, small in number and, with one special exception, small in size, which exhibit the appearance of discs having well-defined boundaries and a central light spot, and which are of uniform luminosity, which features caused them to offer considerable resemblance to certain of the planets. 07 M. Uranus Majoris is one such object, and has been described as having a diameter of 24°. Lord Rosse's picture of it evidently justifies the name of "Owl Nebula" which he gave to it, albeit his picture negatives the general description of these planetary nebulae given by Sir W. Herschel in his paper on this paragraph. The planetary nebula which I mentioned just now as presenting the features of an owl is 37 GJ IV. Draconis, as viewed through my 6-inch telescope, shows a similar feature; but the 18-inch scope will bring out the details which Holden has described. Planetary nebulae seem to possess some peculiarities which differentiate them from nebulae generally. The great majority of them are situated in, or close to, the Milky Way. Very few are much more numerous in the Southern Hemisphere than in the North. Fig. 291 PLATE XCVI. A starry sky with a large, dark nebula in the center. The Nebula 4620 h - 58 M VIII. Cygni (E. E. Barnard). 1234 Fig. 252 PLATE XCVII. The Nebulae 81 and 83 M. and a nebulous Star in Ursa Major (Isaac Roberts). [335] IRREGULAR NEBULA. 335 Northern ; they are most of them gaseous, according to spectroscopic observations ; and many of them seem to exhibit a bluish tinge of colour. " Nebulous stars " can only be described as stars which are surrounded by—or, perhaps it will be better to say which seem to be surrounded by—a nebulous atmosphere, of indefinite form and outline. Hind remarked that the stars thus enveloped have nothing in their appearance to distinguish them from other objects, and institute of such appendages." The brightest nebulae so recognised as such, is 4 Orionis, of which, though the star which is generally named as the "nebula" is representative of its class is 46 I V. Germanus, Sir John Herschel describes as an 8-magnitude star "a very large and luminous centre of an exactly round bright atm- osphere," or "nebula." There are not many of these stars known, and the few there are cannot be usefully observed except with large telescopes. The 6th and last class of nebulae which require notice are elongated in form and large size. Though most of them which will now be mentioned are discernible in small telescopes, yet here, again, instruments of great light-gathering power are necessary for their examination. Mention has already been made of the "Great Nebula in Andromeda," which, for some reasons, might with propriety be Sir J. Herschel (frontispiece). Figs. 293 and 294.--Planetary Nebulae 97 M. Uran Majoris. Generally known as "The Owl Nebula." 336 236 enrolled in the class which we are now considering, especially on account of its size and brilliancy, and because its elliptic form is so remarkable. The 5th star, the "Great Nebula," in the head of Eridanus, disappears almost entirely with optical assist- ance on a large scale. Subject to this remark, the "Great Nebula in the Sword- bear of Orion" may be put first in importance in any list of irregular nebulae. Its size and brightness led to its discovery very soon after the invention of the telescope, and it has reached such a degree of perfection that it surpasses all other ob- jects than any other object in the sidereal heavens. The first feature which immediately forces itself on our attention when it is seen through a telescope is its resemblance to the "Mouth of Fish Mouth," from its supposed likeness to the mouth of various sorts of fish. This is no sooner seen than the second object to attract attention immediately does so, namely, "The Trepanium" of stars, the 6th and 7th stars. These two stars, being close together at their near neighbours, is generally spoken of as a "multiple star." The largest member of the family being #, the use of the word "Trepanium" is not applicable to it, but it is used for those stars close at hand to make up the figure which geostriamists call a trepanium; but this is not the end of the matter. We have already remarked that it was not without difficulty the 4 special stars, a 5th and 6th come into view when more telescopic power is available; indeed, these 3d and 6th stars constitute a very good test of telescopes of 5 or 6 inches aperture. In fact, it is only when these four stars are seen that many more stars exist in or closely adjacent to the Trepanium, bringing up the total number to 9. The existence of these 3 supple- mentary stars has been denied by some astronomers, who have been vehemently disputed. A fair summary of the situation appears to be this: that there are other stars in or close to the Trepanium; that they are variable; and that the 6th star itself is variable. But this statement seems undoubtedly true, and if the 3 smaller stars are also variable, we have a com- Figs. 295 PLATE XCVIII. The Great Nebula in Orion (Harvard College Observatory). A starry night sky with a nebula-like structure in the center, resembling a rectangular box with a dark interior and a lighter exterior. The nebula is surrounded by stars and other faint celestial objects. 236 Fig. 296 PLATE XCIX. The Great Nebula in Orion (W. E. Wilson). [337] THE GREAT NEBULA IN ORION. 337 plete explanation of the contradictions which have been indulged in on the subject. This nebula, as a whole, illustrates in a striking degree the discrepancies which constantly present them- selves between hand-drawings of sidereal objects and photo- graphs. The hand-drawings of this nebula all fail to do more vey the idea of a flat patch of nebulous matter. Or, if this state- ment is too de- nite, it can cer- tainly be said that they will convey any suf- ficient indica- tions of the diloculent truth which is such a special feature of all the photographs which I have ever seen. It is the existence of masses of seemingly fluculent material which makes it so difficult to accept any theory that nebulae, such as this one, are masses of nebulous gas. The nebula known as 30 Doradus is a very singular one, A diagram showing two stars labeled "A" and "B", with a third star labeled "C". The diagram is annotated with Greek letters and numbers. A diagram showing three stars labeled "A", "B", and "C". The diagram is annotated with Greek letters and numbers. A diagram showing four stars labeled "A", "B", "C", and "D". The diagram is annotated with Greek letters and numbers. A diagram showing five stars labeled "A", "B", "C", "D", and "E". The diagram is annotated with Greek letters and numbers. A diagram showing six stars labeled "A", "B", "C", "D", "E", and "F". The diagram is annotated with Greek letters and numbers. A diagram showing seven stars labeled "A", "B", "C", "D", "E", "F", and "G". The diagram is annotated with Greek letters and numbers. A diagram showing eight stars labeled "A", "B", "C", "D", "E", "F", "G", and "H". The diagram is annotated with Greek letters and numbers. A diagram showing nine stars labeled "A", "B", "C", "D", "E", "F", "G", "H", and "I". The diagram is annotated with Greek letters and numbers. A diagram showing ten stars labeled "A", "B", "C", "D", "E", "F", "G", "H", "I", and "J". The diagram is annotated with Greek letters and numbers. A diagram showing eleven stars labeled "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", and "K". The diagram is annotated with Greek letters and numbers. A diagram showing twelve stars labeled "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", and "K". The diagram is annotated with Greek letters and numbers. A diagram showing thirteen stars labeled "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", and "K". The diagram is annotated with Greek letters and numbers. A diagram showing fourteen stars labeled "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "AA", "AB", "AC", "AD", "AE", "AF", "AG", "AH", "AI", "AJ", "AK", "AL", "AM", "AN", "AO", "AP", "AQ", "AR", "AS", "AT", "AU", "AV", "AW", "AX", "AY", "AZ". The diagram shows a star at the center, surrounded by a ring of smaller stars. The ring consists of 14 stars, each labeled with a letter from A to Z. The outermost star is labeled N. The innermost star is labeled AA. The second star from the center is labeled AB. The third star from the center is labeled AC. The fourth star from the center is labeled AD. The fifth star from the center is labeled AE. The sixth star from the center is labeled AF. The seventh star from the center is labeled AG. The eighth star from the center is labeled AH. The ninth star from the center is labeled AI. The tenth star from the center is labeled AJ. The eleventh star from the center is labeled AK. The twelfth star from the center is labeled AL. The thirteenth star from the center is labeled AM. The fourteenth star from the center is labeled AN. 238 GROUPS OF STARS AND NEBULES owing to the strange convolutions of the nebulous matter, which almost defy description. It is faintly visible to the naked eye, of course, but it does not attain the limits of the Nebulae Major, to be presently described. The nebula surrounding the star $\gamma$ Argus is another very remarkable object—remarkable alike from its special features as well as from its position. In 1780, and again in 1781 and 1783 and following years, he gave very careful attention to this nebula and to the position of the chief star in it. He specially pointed out that the star was surrounded by a dense cloud, and that the star was wholly surrounded by nebulous matter. He remarked that "It is not easy for language to convey a full impression of the beauty of this object." (See Plate I.) This shows this star, when it enters the field of the telescope (figured in R.A.) by the diurnal motion, ushered in as it is by no glorious and innumerable procession of stars, to which it forms a sort of halo. The first mention of this object was made by Sir William Herschel in 1805 by a statement, put forth by a Tasmanian observer named Abbott, that the void space had altered in form, and that the star had changed its position. These statements were made with great confidence. These allegations were proved to have been quite unfounded, and it is difficult to realise how Abbott could have been led to make them. Herschel had published, in connection with his observations on the nebulae, a drawing of $\gamma$ Argus. A few years afterwards, that his drawing still represented accurately the general appearance of the object. This star is one of the chief members of an important group which, perhaps, would be better described as a single mass of nebulous matter pieced together and exhibiting a beautiful spiral form. The chief star is situated in a vacant area, abruptly and unceously crooked, and quite void of nebulous light." This is Sir J. Herschel's description of it, and he goes on to say that a beautiful triple star $\gamma$ is situated precisely on the edge of one of these nebulous masses, just where the interior vacancy forks out into two Fio. 238 PLATE C. The Nebula surrounding $\eta$ Argus (C. E. Peck, 1882). 238 Figs. 209 PLATE Cl. The Nebula surrounding Arpil. [439] NOTEWORTHY NEBULAE. 239 channels." This nebula is sometimes called the "Trifid Nebula in Sagittarius." It is unfortunate that Sagittarius should be a constellation not very favourably situated for observation in England, for in the nebula 8 M. Sagittarii we have another striking object which is visible to the naked eye, namely, the Horse-shoe nebula and stars in the same field. It is an interesting question in regard to cases such as this whether any relations subsist between matter and the stars; that is to say, whether the stars are actually connected with the nebula, or are merely optically associated with it. The question is one which, in general, can only be decided by a majority of individual opinion. I have already stated on a previous occasion my strong conviction that, in the case of the temporary star which burst forth some years ago in the constellation of Andromeda, in viewing the star, we were looking at an actual nebula, and not at a star which was to be in front of the nebula, and had no connection with the nebulous mass which we saw in the background. The nebula 8 M. Sagittarii may be detected by the naked eye, but, of course, it requires a telescope to bring out its features. In the constellation known indifferently as Scutum Sobieskii, or Scutum Sobieski (Chamber), we have a nebula (17 M.) which is often called, but not very judiciously, "The Horse-shoe Nebula," though now the name of "The Omega Nebula" is more gener- Fig. 300.—The Nebula 17 M. Gypel Sobieskii (Chamber). In this nebula we have a nebula (17 M.) which is often called, but not very judiciously, "The Horse-shoe Nebula," though now the name of "The Omega Nebula" is more gener- 240 GROUPS OF STARS AND NEBULAE. ally and properly attached to it. In real truth, when seen at its best, the appearance of Greek omegas coupled together at their bases by a bar is not unlike that of a nebula. To the amateur with a small telescope must be satisfied if he makes out the shape of this object to be that of a swan without legs. One needs a large telescope to see the true nature of the group, which consists of changes in nebulin, but there does appear to be some evidence that, within 30 years of Sir John Herschel's careful researches on this subject, his work was not sufficiently appreciated by experienced observers and draughtsmen. The next object which comes before us is the Order of Right Ascension, a nebula which is commonly called "The Dumb-bell Nebula in Vulpecula". The name is very appro- priate in speaking of it after viewing it with a telescope of moderate aperture. The effect produced by the telescope is such that the greater optical power so completely transforms its appearance that the idea of a dumb-bell quite passes out of one's thoughts. The truth of this statement will be readily realised by examining the successive photographs (see Figs. 301-304). In a small telescope it appears like a somewhat round nebulosities in contact. Sir J. Herschel saw it with "a very small telescope" and described it as "a cluster of several masses"; but Lord Rosse's 3 reflectors made material changes in its appearance. His 3d. reflector destroyed the regular elliptical form given by Sir J. Herschel, while his 6th. re- flector brought about what may be considered as striking transformations and introduced a considerable number of stars individually recognisable as such. The Southern Hyades pugnus furnishes a striking nebulous aggregation (No. 458 of Herschel's "General Catalogue"). This has been described as a very large space 20° or 30° long in Declination, and 1 hr. or more wide in R.A., full of stars and nebulosities. The Southern Hemisphere contains 2 objects, known re- PLATE CII. Figs. 391-392 A starry sky with two bright objects, one larger and more prominent than the other. The Death-bell Nebula in Vulpecula (B. S. Wilson). Taken from a negative. Low power view. Figs. 303-304 PLATE CHIL (Shmidt) The Dumb-Bell Nebula in Vulpecula. (Land of Roses, 1st Refraction.) A starry sky with a nebula shaped like a dumbbell. The top part of the dumbbell is brighter than the bottom part. [2406] Plate 305-306 PLATE CIV. Nebulous Region of ρ Ophiuchi. Nebulous Region of γ Cygni (E. E. Barnard). 2408 Nebulosity not visible in telescope, but disclosed by photography. Fot. 307 PLATE CV. A starry sky with a nebula-like structure in the center. The Nebula 14 by V. Cygni (Lick Observatory). [2456] Fm. 308 PLATE CVL The " Trifid Nebula" in Sagittarius. 24 of 1 Fig. 399 PLATE CVII The " Trifid Nebula" in Sagittarius. 2406 Fig. 310 PLATE CVIII. Stars in Cygnus (Henry, at the Paris Observatory). 1407 PLATE CIX. Fig. 311 The Nebula Major, or Large Magellanic Cloud. A black and white photograph of a starry sky with a prominent spiral galaxy in the center. 1408 Fig. 113 PLATE CX. A starry sky with a bright, round object at the center, surrounded by a faint, spiral pattern of stars. The text "The Nebula Minor, or Small Magellanic Cloud." is written below the image. 206A Figs. 313-314 PLATE CXL Double Cluster in Perseus. A star cluster with two main clusters separated by a dark space. The left cluster is labeled "S" and the right cluster is labeled "W". Below the clusters, there is a large dark space labeled "N". To the right of the dark space, there is a smaller cluster labeled "E". Black space void of stars with Constellation Sagittarius. 104 DISTRIBUTION OF NEBULA IN THE HEAVENS. 241 specively as the Nebulae Major and the Nebula Minor, which are large patches of nebulous matter which received their names from their resemblance to the nebulous and extensive size. The former is in the constellation Dorado, and the latter in Toucan. Both are visible to the naked eye on a dark night, but the smaller one is overpowered by moonlight. Sir J. Herschel, in his "Catalogue of Nebulae," gives 300 clusters, and nebulae of every description. The larger one is about four times the size of the smaller. I am not acquainted with any other writer who has given more than this number. Unfortunately, the Southern Hemisphere seems altogether lacking in astronomical authors who might write books describing what they had seen in the same way as the multitude of writers have described the Northern Hemisphere. In attempting to describe, the celestial sights visible in the Northern Hemis- phere. This absence of literary enterprise on the other side of the world is very remarkable, and it is difficult to draw largely on the great work published in 1847 by Sir J. Herschel, in which he recorded the results of his observations as far back as 1834 and subsequent years. A chapter on dust and gas would not be complete without some allusion to their distribution in the sky, which is exceedingly irregular. Subject to certain special exceptions, these two elements are distributed fairly evenly over the whole sky; but this is a long way from being the case with the nebula, as will be shown later on. The following table (p. 256) is taken from "Catalogue" of 5091 of these objects, which was published in 1864. An examination of this volume discloses the follow- ing facts: While Horsley's House of Science includes 686 nebulae including clusters, and House XI. 421, Hour XIX. has only 70, and Hour XX. only 90. In other words, the constellation Virgo and its neighbours Results of Observations made during the years 1834-3 at the Cape of Good Hope. 16 242 GROUPS OF STARS AND NEBULE. include 5ih of the total number of nebulae recorded up to the middle of the 19th century; and I do not suppose the rela- tive proportions have been seriously destroyed by the later discoveries. The Milky Way is by far the most abun- dant in nebulae, whilst the two richest regions are those which lie at the 2 poles of that great belt. Another characteristic of the Milky Way, which is also its most important, is that the great majority of the nebulae indicated by the spectroscope to be gaseous are situated either within or on the borders of the Milky Way, whilst in the regions near the poles they are very rare indeed. In other words, whilst there are plenty of non-gaseous nebulae situated in those localities, this chapter must not be closed without a few words re- specting the Milky Way itself, because it is one vast nebula running right round the heavens in the form of a belt, or ring ; at the same time a description of its course, if put into words, would be tedious and uninteresting. It is therefore best wishing to follow it right round the heavens through the various constellations can do so in no better way than by patiently going over all the stars and nebulae mentioned in my lines of Astronomy in his hands'. It is long and elaborate, but very carefully framed. Suffice it, then, to say that the course of the Milky Way is a great circle of about 60° to the equator cutting that in R.A. 6h. 47m., and 8h. 47m. From this it follows that its northern pole is situated in about R.A. 12h. 30m., Declination +27°. This position may be considered to be at 6h. 47m., and Declination +27° S. Passing over the numerous and varied attractive features of the Milky Way, I will now proceed to describe some of those details here, mention must be made of a singular void space in the constellation Sagittarius, the precise position of which * Herschel's description has been republished in my Handbook of Astronomy, 4th edition, vol. iii., and some other modern works.

THE SILKY WAY. 243 is R.A. 17 h. 16 m., and Declination 27° 5' S. This black hole is almost circular, and on the N.W. of it there are 4 stars, the brightness of which is equal to that of the Sun. To the E. of this hole there is another void space in the shape of a narrow crescent; but this space appears less black and less sharply defined than the first. My last words here will be to recall the fact that, strange as it may appear, the idea of split milk is associated in several languages with what we still persist in calling "The Milky Way." It is thus clear that the Milky Way has been the subject of grotesque nomenclature and fantastic speculations. Whilst the grotesque nomenclature may be said to have ceased, I fear it cannot be said that, though we have reached the 20th century, fantastic speculations have come to an end. CHAPTER XIII. THE CONSTELLATIONS. The subject one of great interest.—The best way of learning their posi- tions and names is to observe them with the naked eye—The Southern spheres.—The constellations best learnt in the open air—List of stars of the Northern Hemisphere—The constellations of the Southern Hemisphere—Alignment of Stars—Origin of the constellations—Modern additions.—A hasty survey of the Northern Hemisphere. A very attractive chapter might be written on the constella- tions in history and poetry with respect to their origin, meaning, and significance. The astronomer would find it difficult to put it moderately, of not less than 3000 years; but it would be foreign to the design of this work to deal with the subject from these points of view. It is rather intended to show how interested the antiquarian than of the astronomer. The scope of this work is so essentially to present the useful and practical side of things that I must bear in mind the temptation to stray away from the main thread which has been pursued on me. An account of the constellations in detail has been formed into an independent chapter (part) to facilitate their study in the open air. This is done because it is impossible to avoid at least the unavoidable distractions of having to handle a star-atlas and a lamp. I thus limit the suggested impediments because many years experience has taught me that it is better not to try to do too many things at the same time and therefore I am very strongly the importance of earnest efforts to become familiar 44 HOW TO STUDY THE CONSTELLATIONS. 245 with the constellations in respect to their positions and the names and situation of the principal stars in each. It is not easy to give a clear and exacting down to describe the constellations with an educational idea in view to treat each constellation as if it were a parish in a country—a geographical description of the whole world. The pointing is a way of looking at the constellations which must be carried out with great discretion and considerable reserve, because it is often apt to lead to stars and other objects being lost for the purpose of the pointing. It is well to remember that we take our eyes out of sight whilst the student is looking another way. What I mean will be better understood if I put it in this way. When one is going to a place where he has not been before, and has not spent a night's work, let him begin by ascertaining what con- stellations are on the meridian when his work begins, and having just made his observations, let him by means of the map find those which are on the meridian in the extreme South (this for England), and then work backwards northwards on the same R.A. towards the North Pole behind him. He need not trouble himself about the stars which are on the opposite side of the Pole, because these are visible all the year round, and therefore are always within his reach ; but I do urge very strongly the advantage of knowing what is on the meridian at 6 A.M., which is on or near the meridian, and taking up his objects selected for study as they severally come to meridian, and guarding his eyes and thoughts from wandering prematurely, so that he may not lose sight of any star belonging to any one constellation. One thing is quite certain : the constellations, as regards their relative positions, can only be effectively learnt by means of comparisons of the facts given in a map. Whilst there are many star-atlases and planispheres in circulation nowadays, there are undisputed advantages attending the use of a book in which stars are portrayed in white on a dark blue or black background. I have therefore used during 246 THE CONSTITUTIONS. many years, with very satisfactory results, the star-maps in Keith Johnston's Atlas of Astronomy edited by Hind. Next after this I would name McClure's Atlas published by the Society of Arts, London, which is a very good English edition of a well-known German atlas, originally compiled by Heis of Münster; but McClure has greatly improved it, and has added many new stars, and also points on white paper. There is also given a deal of information descriptive of the most striking stars and clusters of stars and nebulae which deserve attention. Of late years Mr. C. J. Kullner, of Syracuse, N.Y., has invented a "Star-pointer" somewhat in the form of an Equatorial quadrant, so far as its fundamental principle is concerned. This instrument has been adopted by many astronomers, and has a large amount of acceptance in America, though I do not think that the instrument has yet become known in England. The engraving will give some idea of the construction and elaborate design. Regarded as an Equatorial in principle, the arrow takes the place of the telescope tube. The instrument must first be placed facing N., and the dials set for the day and hour; then the observer turns his head to face the desired constellation, and further change. Star-maps on the dial show the grouping of the stars in their actual position as seen in the sky, and the arrangement of the dials shows the time at which each star rises or sets on the horizon or not, and if the desired constellation is not visible at the time, then, by revolving arrow and dial, the time of rising can be found. The instrument stands about to inches high, and it is used in a dimly lighted room. It is useful at any latitude in the Northern Hemisphere. Conversely to finding a constellation or bright star which it is desired to find, it may be used to find a star whose declination is known, by turning towards which the arrow is directed. It also shows sidereal time, which is read off opposite the graduation for March 21. An incidental, but often very useful, item of information, which can be arrived at with the assistance of the printed instructions KULLMER'S STAR-FINDER. 247 supplied with the instrument, is this : where a given con- stellation or position in the heavens will be (so far as the observer can see) at any time (when it is concerned) in the sky on a given day. Such informa- tion is of great use to an observer who, knowing the expected position, say, of a new comet on a given day, wants to know when he shall at what hour, such comet will be above his horizon so that he may have the chance of seeing it. Were Dr. Kull- mer's invention to become generally known in England it would be of great service to request, for we have nothing of the kind in use in this country. I will suppose the reader to have made himself ac- quainted with the apparent sines and positions of some of the stars, and that he intends to get up the whole subject of the constellations in a systematic manner. The means for doing this will be found in a chapter specially devoted to the constellations in date, and which will contain a variety of general con- siderations relating to the stars. It is assumed that the reader is standing out in the open air, Fig. 315.—Kullmer's "Star- finder." A diagram showing a star-finder device. 2 See Chapter XIII (foot). 248 THE CONSTELLATIONS. if possible in some elevated position, with as large an expanse of sky as clear of terrestrial obstructions, as possible, and that he be armed with a telescope, so as to see something in the nature of a bull's-eye lantern, which may be either of the common type, and burning oil; or, better still, that he has a portable electric light. The first thing to be attempted is to try and identify the brightest stars, which are those of the 1st of the 6 magnitudes which are regarded as constituting the stars visible to the naked eye. This is useful to give a list of the stars (1) in the order of brightness, and (2) in the order of their Right Ascension; that is to say, in the order in which they successively rise, come to the meridian, and set. FIRST-MAGNITUDE STARS IN ORDER OF BRIGHTNESS.
a Canis Majoris (Sarvaj)
b Argin (Celadon) not visible in England.
c Coma (Coma) Not visible in England.
d Boöis (Aurorae)
e Oriens (Oriens)
f Auriga (Cepelia)
g Lyræ (Lyræ)
h Canis Minoris (Pisces)
i Oriens (Oriens) Not visible in England.
j Eridani (Eridanus) Not visible in England.
k Tauri (Tauri) Not visible in England.
l Crocius (Crocius) Not visible in England.
m Scozia (Scoziae) Not visible in England.
n Aquila (Aquila) Not visible in England.
p Virgo (Virgoe) Not visible in England.
q Fossus Australis (Rosae/Australis) Not visible in England.
r Crocus (Crocus) Not visible in England.
s Geminorum (Gemini/Aurorae) Not visible in England.
t Locius (Locius/Aurorae) Not visible in England.
u Cygni (Cygni/Aurorae) Not visible in England.
8 Centaurii (Centaurii) Not visible in England. 9 Tauridii (Tauridii) Not visible in England. 10 Scorpii (Scorpii) Not visible in England. 11 Aquariidii (Aquariidii) Not visible in England. 12 Lociidii (Lociidii) Not visible in England. 13 Cygni (Cygni) Not visible in England. 14 Lyrae (Lyrae) STANDARD STARS. 249 FIRST-MAGNITUDE STARS IN ORDER OF RIGHT ASCENSION.
h. m.
a b c
e Eclipta (Acheronar) 1 34 57 41
a Aquila (Capella) 1 34 58 06
a Auriga (Capella) 5 40 43 54
a Orionis (Betelgeuse) 5 50 73 23
a Canis Minoris (Sirius) 6 60 16 35
a Canis Majoris (Sirius) 6 60 16 35
a Canis Minoris (Procyon) 7 34 27 27
a Canis Majoris (Procyon) 7 34 27 27
a Leonis (Regulus) 10 55 12 83
b Cephei (Vespera) 12 49 19 19
b Cincius (Vespera) 12 49 19 19
b Centauri (Antares)
Sextans (Antares)
                                                             April 21
Sextans (Antares)</thead> </thead> <tbody> <tr> <{<table border="1" cellspacing="0" cellpadding="0">} <tbody> <{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing="0" cellpadding="0">}<{<table border="1" cellspacing= 250 THE CONSTELLATIONS. will serve to give him an idea of where the respective constellations lie, and indirectly where the other constellations are to be found; whilst the second list will help him to recognise a star of a magnitude greater than that which he can see with his naked eye. One of the most worrying difficulties which has to be faced in simply stating the positions of the varying positions which they occupy between their rising and setting. This really amounts, more or less, to their being upside down at setting, compared with their position at rising. The fact that this is so, and that informa-tion is another reason for students confining their attention as much as possible to constellations which are on the meridian at the time that study is going on; or, at any rate, to constella-tions which are on the meridian when they are looking up at the meridian. The fact that such upside-down changes do indeed apparently take place will be better realised by an examination of the following diagram than by any attempt to explain the matter verbally. Having identified a few conspicuous stars, the student must habitually observe, first, whether he can find a certain constellation in the heavens, and then whether he can pick out a star to associate with either literally on his map or mentally in his head; and then to seeing whether he can pick up in the heavens a particular object he wants by running his eye across the sky from one star to another. In order to do this, he must mentally reproduce by recalling his map. This pro-cess of star-hunting is technically called "allination" or "alignment". It is not necessary for him to know how to do it, and the student must learn to do it for himself by the exercise of thought and ingenuity. For instance, if he sees certain stars in a certain constellation, and if he knows that a certain constellation is so much, and that the small star $\beta$ which he wants to look at is in the same straight line with $a$ and $\beta$ and thus of the distance beyond $\beta$ that $j_1$ is from $a$, he must estimate, by more than one attempt perhaps to see, when looking up at the stars, whether $j_1$ forwards from $\beta$ A diagram showing a star map with various constellations marked. STAR CATALOGUES. 251 will take him : then, if his estimate on the map is fairly correct, and if he is able to estimate where Joth will take him on the map, he can easily find the star which he is looking for which he is looking in the place where he ought to find it. This method of finding unknown stars by means of imaginary lines drawn out from the map is only of use when one is accustomed to the use provided with an equatorial telescope with its customary Right Ascension and Declination circles. There are various popular star-charts and books with diagrams showing how to find the position of a star by means of lines either between different stars. Some of these books will be useful to the tyro, but it is not unfrequently happens that the con- struction of such diagrams is so poor that they do not disfigure the plates, but embarrass the eye in consulting the plates. Though I do not intend to give a detailed statement of the constellations on their historical site, it may be well just to mention some of them. It was not until 1608 that this purpose, as far as back as Polewine, who flourished 1600-1700 at Alexandria. He enumerated 48 Constellations, 21 of which were new, and 27 were borrowed from the Greeks. In 1610, John Flamsteed, who died in 1610, added 19. Bayer (he of the Atlas) added, or rather perhaps accepted as additions, 12 constella- tions from the Greek writers, namely, Rhoxylos and Halley, about the same period, added 4. Robur Caroli, to count the oaks of King Charles II. Flamsteed's maps contain 29 constellations, presumably invented by himself; and Hevelius in his catalogue of 1690 mentions 37 constellations, nearly all of them Southern, were set up by Lacaille and others. Many of these 18th-century additions were afterwards rejected by Flamsteed himself, and many of which will explain names appearing in books and maps pub- lished a century or so ago which are not now to be found in modern maps or in modern lists. The total embraced in the statement just made amounts up to top. Even that number does not exhaust the names which have 252 THE CONSTELLATIONS. been proposed but promptly ignored. The situation was well summed up once by Sir J. Herschel, who causally wrote as follows:—"The constellations seem to have been purposely named after the most conspicuous stars in each group, so that their visible position may be considered as a convenient and agreeable possession." Innumerable snakes twine through long and contorted areas of the heavens, where no memory can follow them. The constellations of the Southern and Northern and Southern, confide all nomenclature.* Constellation reformers have, as was to be expected, sprung up at various times, but, as often happens with reformers, they do not always succeed in what they propose. There is especially unworthy of thanks, owing to their reckless and ill-advised schemes of reform, namely, Dr. B. A. Gould and Mr. H. C. Rowan. Subject to reservations which have already been laid down, the following may be offered as a brief general summary of the principal features of the constellations of the Northern Hemisphere.* We will start with Ursa Major, the Great Bear, the most conspicuous of the constellations which never set in Great Britain, Canada, and the Northern States of North America. The three stars (α, β, γ) of this constellation are known as the α (a), β (b), γ (g), have long been compared to a wagon, the other 3 (ε, ζ, δ) being the horses ; or the 7 taken together make a figure of a bear with outstretched arms and legs. The wheels, or the two furthest (β, α) from the horse's head, are known as "The Pointers," because they point to the Pole-star (a Ursae Minoris) at the tip of its little Bristle tail; and farther on stand out two more constellations, Cassiopeia situated in the Milky Way where it is nearest the Pole. Cassiopeia includes several bright stars so grouped that they form a figure like a ship with sails hoisted; when these are viewed. The two most northerly wheels of the wagon (α, a Ursae Majoris) point to the bright star Capella (a Aurigae), which is also circumumporal in our latitudes. * Condensed from my Handbook of Astronomy, vol. iii. CONSPICUOUS ISOLATED STARS. 253 The stars in Ursa Major may be usefully employed as scales of distances for degrees of arc. The nearest "pointer" (α) is 28° from the Pole ; from α to β is 3° ; from β to γ is 8° ; from δ to ε is 4° ; from δ to ι is 6° ; from ε to η is 7° ; from η to ρ is 10°. Descending diagonally across the heavens along the Milky Way from Cassiopeia towards Capella we come to a Perseus, and a little further on to the variable Algol (γ Persei); if we follow the line of the Milky Way through the constellation of Perseus, we shall arrive at Cygnus, whilst beyond this and a little out of the Milky Way is Vega (α Lyrae). Draco includes a long chain of stars which form a sort of tail, and Pegasus occupies the space bounded by Cassiopeia, Cygnus, and Draco, is Cepheus. Another very conspicuous group in the Northern Hemisphere is that of the Great Bear (Ursa Major), known also as Pegasus, as pointing directly towards it, are two conspicuous stars in Andromeda (α β), and a third (γ) is a little beyond them. Andromeda, as a constellation, will be readily known by the three stars in its body, called the "Worms" (Pegasus α β γ), which make up the Pegasus "square." An imaginary line through the Great Bear and Capella will reach the constellation of Orion, and passing through its right angle towards the Milky Way, will reach Aldebaran (α Tauri) and the shoulders, α, ν, of Orion. Orion is the most striking constellation in the whole heavens, comprising as it does so many bright stars. The lack of astronomical knowledge in high places is amusingly and often amusingly illustrated by Mr. J. Stuart in his book "Reminiscences." Alluding to conversations he had had with Mr. Gladstone, he says—"It was only when I was about twenty years old that I first saw Orion; I remember when he had been looking at the star—Why is it that the Great Bear seems so much more interesting than Orion?"—and then he adds—"Because it never sets." He said, "Do you mean to say that it never sets?" I thought at first that he was mistaken; but when I explained the matter to him it struck me that he was right. It is true that Orion never rises; but in Homer's phrase, "et éon," applied to the Great Bear—that is to say, "late in time"—it has always been regarded as a morning star.— J. Stuart, Reminiscences, London, 1924, p. 269 254 THE CONSTITUTIONS. many conspicuous stars, namely, α, β, in the shoulders, A, B, C of the belt, and ε and ι in the legs. Aldebaran is a star of reddish tint and the most conspicuous member of the cluster of the Hyades, which is not far from the Pleiades. Aldebaran, the Pleiades, and Algol make the upper, while α Ceti with Ariadne and η Cassiopeia form the lower. W. The head of Ariadne is denoted by two principal stars (α, β). A line from the Pole-star takes midway between the Great Bear and the Little Bear to the constellation of Cassiopeia, the two well-known stars Castor and Pollux; continuing southwards it will meet Procyon (a Canis Minoris). From thence, by bending the line across the Milky Way and carrying it as far again, it will reach Sirius (a Canis Majoris) and so southwards to a Columnar Noachi. Algol and α Bemelmens are at equal distances (a Leonis) from the Pole-star. The tail of Leo points with Leo's tail to the other end. S. of and preceding Regulus is Cor Hydrea (α), the space between them being occupied by Scorpius. The Pole-star and the middle horse of the Great Bear (γ) direct us to Spica (a Virgo) at a considerable distance, whilst beyond and in the horizon will be Centaurus. The head of Hercules is a conspicuous Great Bear (point nearly to Arcturus (a Boötes), which forms with Spica and Rigel a splendid triangle. In a southerly direction another triangle is formed by Vega (a Lyrae), Arcturus (a Boötes), whilst the head of Hercules and the head of Ophiuchus lie between Lyra and Scorpio. In the northern sky is a large constellation called Orion, from Arcturus through the head of Hercules, is Altair (a Aquilae), which makes, with Vega and a Cygni, a conspicuous triangle. Closest to this is Delphinius, a small constellation with 9 other conspicuous stars. Two of the stars in "The Square of the Pegasus," already THE ZODIACAL CONSTELLATIONS. 255 mentioned (a), point, at double their distance, southwards to Fomalhaut (a Piscis Australis). The line of the Ecliptic may without difficulty be traced by the eye by means of the stars now to be enumerated. Not far from the Ecliptic itself are the following constellations (b), viz., the Little, or the Ecliptic. To the N.W. of Aldberac, at some distance, is the chief star of Aries (a), whilst to the N.E. of that star are α and β Geminius. Regulus (a Leo) is situated between these two stars, and is a little S. of it. The Ecliptic thus known, the zodiacal constellations may be easily distinguished in their successive order from W. to E. In the first place, we have the constellation of Cancer, with its two stars, α and β, which are situated near each other on the N. and Cetus on the S., the 3 constellations reaching nearly from the horizon to the zenith; Taurus will be recognised by α Pleione, ι Aldberac (a) and the Hyades; Gemini by Castor and Pollux (c); Cassiopeia by its two stars, and by the signs of the signs, by the cluster Perseus, but as a constellation, having no stars larger than α, and that only of mag. 3 ; Leo by α and β Leonis Minoris; Virgo by α and β Virginis; Libra by β (which, however, is only of mag. 2); Scorpio by its two red stars Antares, and ι other stars of the 3rd magnitude; Sagittarius by its two stars ι and ο; Aquarius by its sign; Capricornus, with its ι of mag. 2; Aquarius, under the neck of Pegasus, with no stars as bright as mag. 3; and Pisces, between Pegasus, Andromeda, and Cetus. It must be understood that the foregoing paragraphs are very rough as regards the information they give, and do not embrace all the constellations of the Southern hemisphere, which are invisible in England. A diagram showing the zodiacal constellations. CHAPTER XIV. TELESCOPES. Telescopes are two kinds—Reflectors, Refractors.—Various kinds of reflectors.—Brief description of each.—Principle of a refractor.—Photographic telescope.—The reflecting telescope.—Standards for telescopes.—Importance of a good stand.—Equatorial mounted telescope.—The altazimuth telescope.—The refracting telescope.—A telescope—Drawing- cloth—Sideral clock—The housing of a telescope—Advantage of an observatory—Detailed description of how to build one. THIS chapter is not intended to be either a treatise on optics, or even a full statement of the different classes of instruments used in astronomy. I only propose to offer some information likely to be useful to amateurs able and willing to give a certain amount of time and lay out a moderate amount of money in the purchase of instru- ments suitable for observing some of the more exelential objects which we have located in the preceding pages. TWO KINDS OF TELESCOPES. Telescopes are two kinds, and there is a medical difference between them. In a "Reflector" the rays of light coming from a distant object are received on a curved surface of metal, or silvered glass, and reflected back to a "focus," where they are collected by another lens or mirror. This is called the nature of a microscope, and which is called an "eye-piece." In a "Refractor" the rays of light are received by a glass 59 REFLECTING TELESCOPES. 257 lena, through which they pass, and, after passing, are brought to a point called a " focus" where they are viewed by what I have called a sort of microscope, though its proper name is " eyepiece," as already given. To compare reflectors with reflectors as well as their relative merits, we must take into account that measurements in feet and inches of each are not comparable. A reflector 6 inches in diameter is an instrument altogether different from a refractor of the same aperture. The former is much more difficult to make, less handy but, if it must be admitted, is also less costly than the refractor brother; but, notwithstanding these facts, I do not recommend reflectors, for several reasons, and one in particular. The first reason is this: although the size of the mirror of a reflector, is difficult to keep in condition ; that is so; however good its condition at the start, it sooner or later gets out of condition. This is because when it is soon tarnished, if of silvered glass it gets dull and in either case it is troublesome to get at either for moving or cleaning. As regards the second reason, it may be explained that there are some differences which make reflectors of one type quite not so handy as those of another type. There are 3 principal types of reflector in use, namely, the " Gregorian," the " Newtonian," and the " Herschelian." The first two are similar. The 3 former of these are the least inconvenient to use because the mirrors, which are at the eye-end of the tube, being pierced in such a way that they can be turned round freely. In the Newtonian and Herschelian forms the eye-piece and the observer are at the side of the tube, and therefore there has to be a diagonal reflector inside; and the observer, every time he wishes to look through his telescope, has to turn his head so as to twist his body round. A Herschelian reflector, especially if it is a large one, is still more troublesome to work, because the side on which he looks through is always obscured and there will be there also. However, Herschelian reflectors are quite obsolete, and this, to some extent, is true of the Gregorian and A diagram showing the different types of reflecting telescopes. 17 258 TELESCOPES. Cassini's refracting telescope. The real competition nowadays is between Newtonians and refractors, and a purchaser will have to exercise his own discretion in making his choice. The Newtonian has the advantage of being cheaper in price than the refractor, whilst ignorant of its drawbacks, some of which have been stated. It must, however, be confessed that the substitution in recent years of the glass mirror for the metal one has done much to popularise the Newtonian reflector, but the latter has something to do with this. A Newtonian telescope is constructed by allowing light from an object on the outer side, and brings it nearly to a point called the "focus." Such a telescope, in its simplest form, consists merely of a double convex lens placed in a tube, which contains the object of the object to be viewed, while a second and smaller double-convex lens, fixed at the other end of the tube, serves as a simple microscope to magnify the image formed by the first lens. This is called the "eye-piece," whilst the magnifying lens is called the "eye-piece." This is stating the matter in its broadest and most elementary shape. In practice, however, it is found that a telescope with only two pieces of glass combined as stated, practically is desirable to arrange things a little more elaborately. Two simple lenses combined above reveal certain optical inconveniences which arise when they are used together. The result is spherical aberration is that the object does not come to as sharp and defined a focus as is desirable, whilst chromatic aberration arises from the fact that the image of the distant object on view is inconveniently fringed with colour. These two drawbacks, which, when a large lens is used, are very serious indeed (as the expression is) by making both object-glass and eyepiece compound instead of simple; that is, by forming both object-glass and eye-piece of two lenses instead of one. On the right disposition of these lenses, as regards the curvature given to them, depends the success or failure of the **ELEMENTARY IDEAS.** 259 optician's efforts to cure the inconveniences referred to. All this, however, is very technical, and does not concern the general public. The purchase of a telescope is a matter which must be worked out by the optician, and he has nothing to do with them except to pay his purchase-money on the supposition that they have been properly made. In order to understand this point, an optician who has done well will do well to consult an expert friend, if he has one within reach, in order to ascertain both the optical part of his proposed purchase and also the metal work. Up to this point I have been talking of the telescope in its simplest form, but it must be borne in mind that short of a very large sum of money, no useful and profitable astronomical study can be accomplished by the aid of a common opera-glass, binoculars, or field-glass. This specially applies now and again to observations of comets, eclipses, etc., when it is necessary to see the object at close quarters; but else but a small telescopes placed side by side, one for the use of each eye. Such an instrument, in its common form, starts with two eyes looking at the same object. Now, it is evident that, namely, that both eyes of an observer are alike, and that what suits one eye will suit the other eye. This is often not the case with binoculars. Binoculars provided with lenses of different focal lengths are not only not suitable for seeing objects at close quarters, but for the centres of the eyes of one person being at a different distance apart compared with the eyes of another person. In making preparations for carrying on astronomical observa- tions the question turns entirely at the outset on the money available. A telescope costing £100 may be bought for £50 or £60; anything from £5 up to £500. But what I have in view in these pages is an effort to assist in a very modest outlay— say, anything between £5 and £100—leaving the question of an apartment in which to house the instrument to stand over to the end of this chapter, and be dealt with separately. A diagram showing two eyes looking at a telescope. 260 TELESCOPES. STANDS FOR TELESCOPES. When asked, as I often am, to give advice as to the purchase of a telescope one point invariably crops up—the difficulty of impressing on an inexperienced purchaser the importance of providing his telescope, whatever its size or price, with a suitable stand. The usual standard of a good telescope is to be no more than 2 inches, and the cost perhaps £10, the only stand which such a telescope would have, or want, will be a tripod of some sort, either entirely of brass to stand on a table or floor, or partly of wood and partly of metal and combined to stand on the ground. Such an instrument will have 2 motions, up and down and right and left. Now this is all very well for terrestrial objects, but when the objects to be looked at are terrestrial, are very inconvenient and unsuitable in dealing with celestial objects, and for this reason the stars themselves are not suitable for use with this type of diurnal motion (as explained in Chapter XI., note) as it diagonally (or on the skew), and a telescope which normally moves up and down and right and left does not readily lend itself to moving askew. EQUATORIAL STANDS. A telescope mounted so as to follow the movements of the stars requires to be tilted so that the main part of the stand shall always be in line with the horizon. This constant motion of the telescope incessantly from left to right will keep any star once brought into the field of view continuously in view. In astronomical language we say "the Alm-astimuth," and by this word I mean that the stand which we started with, whose technical name is "Equatorial," has been converted by being tilted into an "Alm-astimuth." Various expedients for this conversion have often been suggested, but they are rough and troublesome, and the intending purchaser of a telescope had much better STANDS FOR TELESCOPES. 261 begin at the outset by buying a properly devised " Equatorial Stand," as an apparatus for following the star by one move- ment is technically called. The various stands which are illustrated in this chapter will show the progressive development of stands, from the smallest and simplest to the most elaborate and costly. " Pillar- and Claw" up to the largest and most costly equatorials for general wide celebritiy. It is not contem- plated to give an analytical account of these large instru- ments, but only to make the reader acquainted with such develop- ments of improvements and accessories as will keep the ex- penditure within the limits of £50 or less, of £100. Two things come up for consideration as soon as we have decided on mounting the telescope as an equatorial. (1) Shall the motion of the stand be horizontal or vertical? (2) What is the pushing motion required to keep an object constantly in the field be given by hand or automatically? Fig. 318.--Astronomical and Look-out Telescope ("Pillar and Claw"). 262 TELESCOPES. As regards the stand to carry an equatorial, such stands, in the form of wooden tripods, are easily portable when there is no heavy telescope to support. But there is always a limit of aperture. But an equatorial is short of its special usefulness if provided with setting circles, such as are required to bring it to any given position, without the aid of some instrument known. Even without circles an equatorial stand is wasted if some fixed marks are not available on the ground out of doors on which to place the feet of the tripod so as to ensure the mutual alignment of the axis of the telescope with what is the essential principle of the thing. This difficulty of how to avoid the inconvenience of having no means of knowing where to place up the tripod, after each time it is removed, is sometimes met by an observer erecting in his garden an iron stand as a permanency, and taking out his telescope at night and placing it upon this stand, together with the telescope, every night whenever he proposes to do work. This condition of things secures a certain amount of exaggertion in getting his equatorial into proper position used by him. The same thing can be done by building sheds and forwards between a house and a garden a telescope, and the important parts of its stand, every night that it is wanted is also put in place. This is a very convenient and satisfactory procedure. It is better by far not only to have a fixed stand, but to keep the equatorial head, and likewise the telescope, permanently in place, as it is found that it is much easier sometimes to move than either a shed or a movable top or an observatory with a revolving dome, which obviously sounds much better. ACCESSORIES TO A TELESCOPE. With an instrument properly housed it becomes possible to add, not necessarily at first, if funds do not permit, but later on, a driving-clock. This is simply an arrangement of clock- EQUATORIAL STANDS. 263 work which, when coupled on to the telescope by suitable means, drives or pushes the telescope continuously forwards, so as to keep the object which is under observation continuously in view without the necessity of the observer constantly having to push the telescope—a labour which is not only very tedious but one which hinders him using his hands for making notes or drawings. With a telescope equatorially mounted, and provided with setting circles, and driven by clock-work, a timepiece will be required exhibiting sidereal times; in other words, announcing what is the hour of R.A. which is on the meridian at any given moment. How of R.A. which is on the meridian at any given moment. Of course, a properly constructed sidereal clock, graduated to 24 hours, is desirable, but it is a luxury; and a common French dining-room clock, costing £2 or £3, answers the Fig. 317.—5-inch Portable Equatorial Telescope. 264 TELESCOPES purpose of a sidereal clock if it keeps fairly good time, and if the owner is able to obtain Greenwich time every day or two from a local public clock otherwise. In my early days as a young astronomer I did a great deal of work with such a clock during several years, and had no difficulty in picking out the stars by their positions at any given hour, so soon as I had obtained sidereal time from my make-shift clock, the setting circles of my instrument being in good adjustment. The methods of adjusting an equatorial to fit it for work must be sought for in books specially written for the purpose. THE HOUSING OF A TELESCOPE. What some people would call a telescope-house, as they would speak of a motor-house or a chicken-house, is scientifically called an "observatory." Having had some practical experience in building observatories for myself and friends, in 3 cases for myself and in several cases for friends, it has occurred to me that the usefulness of this book would be increased if I gave some practical hints and suggestions for the guidance of those who possess a scientific interest and who intend to acquire, a telescope large enough and good enough to be worth a permanent fixed shelter. My first observatory was built in 1866, when I put up at Sydenham a wooden observatory, to ft. square, with a revolving roof and walls, wholly constructed of timber, the roof being supported on iron columns which rest on the jointed timbers. I will not further describe this structure, the builder's charge for which was £58, because I have much more recently erected at Sydenham what is more or less a facsimile of this, with some alterations and improvements suggested by the * See, for instance, my Handbook of Astronomy, vol. iii., "Astronomical Instruments." * Fig. 318 PLATE CXII. General View of the Oldastional Figuratorial Instrument. (From The Philosophical Transactions, 1793.) 264 PLATE CXIII. A large white telescope with a long tube and a smaller secondary mirror at the top. The telescope is mounted on a white pedestal with a circular base. There is a small black box attached to the pedestal. **Equatorial Telescope, with Object-glass of 10 inches aperture ( Cooke).** 165 TELESCOPE-HOUSES. 265 experience of years. Suffice it to say, regarding the 1866 observatory, that when this circumstance compelled me to go and reside in a different part of the country I at once found a purchaser for it, who was much struck with the ease and facility with which the whole was taken to pieces and conveyed into his house. In 1860 I went to live in a house at Bickley which had a tower, and, by arrangement with my landlord, I supplied, as the house was then, with a revolving telescope on a 3-in. Cooke equatorial. This mode of wood, weather-boarded, and of practically the same design as the roof erected 3 years previously at Sydenham. In 1864, at a cost of £24, to a house of my own, built after my own plans, I provided a tower about 50 ft high as part of the house, the topmost story of which was built and fitted up as an observatory. The instrument was brought from Bickley. This eventually covered a 6-in. Grubb equatorial, with which instrument I carried on observations during a period of nearly two years. My reason for making the top of the tower appertaining to the house into an observatory was because my 5 years' experience at Bickley taught me the great advantage of so doing. Inducements to observe in cold, wintry weather are very much more effective when the observer is able to walk to and fro about his observatory without being exposed to any difference state of things which he has to face when it is a question of dressing up in a greatcoat and other things preparatory to walking any number of yards in the open air, possibly over snow or ice. Many years ago a writer in Nature made a ridiculous attack on my plea for putting a movable dome on the top of my observatory. He said that if I had done so later, the said roof would be found to have descended into the garden. How baseless this writer's foolish opinion was, is 266 TELESCOPES. sufficiently shown by the fact that my dome passed unscathed through 35 winters and summers at Eastbourne in a situation very exposed to the winds, and was sometimes gale-stormy, whenever they occurred, no other precautions being taken than two ties of not very thick rope. Only once, during the whole length of my stay at Eastbourne, did I have any difficulty in keeping bearings to an extent suggesting that, if the rope had not been there, it might have gone overboard. As a matter of fact, often for many weeks and months together I neglected to tie the ropes on the first day. I proceeded now to describe my fourth observatory, to be seen at Sydenham, which, as I have said above, embodies previous experiments with regard to the construction of domes (though but a 13-sided polygon) has occupied in more than 40 years three different sites, and its timbers, without even the exception of a quadrant, are all original. It is remarkable how much time and labour which they left the carpenter's shop at Uckfield, in which they were originally put together. This last-named fact I attribute entirely to the circumstance that, instead of belonging to a single owner, it was built for several purposes. The cost of paint all at once at long intervals of time, I made it a rule, as far as possible, to put on a single coat of paint something like this. It will be useful to explain the successive steps involved in the erection of an observatory, taking the reader through the actual modus operandi based on the fiction that I am describing. The first step was to find a site where a potomac of which had actually been erected previously somewhere else. A good solid foundation is a sine qua non to start with, for without it a telescope of any considerable weight will constantly be getting out of adjustment, even though there may be no risk of it and its house toppling over. The extent of the risk depends upon the nature of the ground. This is usually a geological question. A rocky, gravel, or chalk soil is usually very stable, A diagram showing the construction of an observatory. Figs. 320 PLATE CXIV. Standard Photographic Equatorial, for the International Survey of the Heavens (Sir H. Grubb). 266 Fio. 321 PLATE CXV A large telescope mounted on a wooden structure with two people standing nearby. 27-inch Refractor of the Vienna Observatory (Sir H. Grubb). 167 A SIMPLE OBSERVATORY. 267 except that rock is often very susceptible to changes of tem- perature, but this was not considered in the construction of dangerous settlements. It is far otherwise, however, with a clay soil. This is a very trying soil to deal with where the stability of a structure of great weight has to be secured in a soil which is liable to be washed away by rain or by any thing from a quarter of a ton to 2 or 3 tons. The soil at Sydenham is a stiff clay, which at different seasons of the year is liable to be washed away by rain, and to show large fall of fissures. Accordingly, to prepare for an observatory the plan of which was to be a square 10 ft. on each side, I excavated a space 12 ft. square in the centre, in deep, and filled it with the broken-bonds of old bricks, broken stone, fragments of brick, old glass, and crockery, and indeed of any hard rubbish for which I had no use, and which I wanted to throw away. This concrete foundation was left untouched, as it happened, for about 3 months, an interval amply sufficient of course, to allow the cement to set. Then a brickwork was built in the form of a dwarf q-inch wall of 8 courses of bricks, the topmost one being formed of bricks on edge sit in cement. It will be understood that so extensive a concrete foundation as that which I provided is quite unnecessary in a general way, and that the only place where concrete is required is at the base of the tower. In the case of this observatory, that it may serve as a base for the brickwork pillar which is to carry the iron stand of the equatorial, premises that the telescope is to be mounted equatorially in the German manner, and that it must be possible for it to be built on concrete must depend on local circumstances. Ordinarily it will not be necessary for observatories of the type described here to have such foundations. I will now give particulars of my foundations. I may as well remark that the large quantity of rough core which I used was A simple observatory with a brick foundation and a dwarf q-inch wall around it. 268 TELESCOPES. rather because I had it and wanted to get rid of it, than because it was really necessary. FOUNDATIONS. The following are particulars of the foundations, and of the cost of the same--- A diagram showing the layout of a telescope observatory. Excavation of ro8 cubic feet (labour) . . . . . 0 12 0 Concrete 72 narrow-loads of broken stone, etc. . . . . 1 10 0 5 bags of cement . . . . . . . . . . . . 16 0 Labour . . . . . . . . . . . . . . . 4 5 0 BRICKWORK IN WALLS AND FLOOR. The foundations being finished, the next thing to be done was to build a dwarf wall running round four sides of a square to support the floor, which was to consist of a wooden frame which constituted the walls of the observing-room; but in ordinary cases this wall would be called upon to carry the whole weight of the building. In order that such a wall may at Sibson's, not have a wooden floor, but to form a floor by means of an additional layer of concrete, rising about 6 in. inside the quadrangular enclosure formed by the brick wall and the outer edge of the foundation. The only objection to such a surface for a room is the facility with which observing chairs or stools, or indeed seats of any kind, can be placed on it. This difficulty is removed by having one or more pieces of wood laid on top of the floor, or one or two pieces of properly seasoned boards (as is often unavoidable when economy has to be considered), is very inconvenient and disagreeable. A concrete floor is, moreover, more easily cleaned and kept clean. The one sole objection that is still held to the feet, but this can be got over by having a mat or Fig. 322 PLATE CXVL Eye-end of the Vienna Refractor. 005 Fig. 323 PLATE CXVII. A large telescope with a long tube and a smaller secondary mirror mounted on top. The telescope is inside a large building with a high ceiling and large windows. There are people working around the telescope. 30-inch Refractor of the Pulkova Observatory (Repnold). 569 **DETAILS OF A SIMPLE OBSERVATORY.** 269 two, capable of being moved from place to place at pleasure. The following was the cost of the— CONCRETE FLOOR.
34 barrow-loads (say 50 cubic feet) of coarse, broken stone. £ . d.
3 barrels of small broken stone, or gravel. 1 8
Mortar, composed of 6 barrow-loads of sand, £1 1 9
Bagged cement for the pavement. 0 6
5 bags of cement for top dressing. 1 0
Labour. 1 0
Total. 7 2
The above cost includes a few bricks, and some cement and labour, for fixing the door-frame, building the pillar for the equatorial stand, and two steps outside the observatory. The lower walls were formed, as has been already stated, of 8 inch thick brickwork, with a course of stone between the bricks on edge. The two first courses in the ground were of common stock bricks, being cheaper than the Sussex red bricks. The upper part of the wall was circular and raised 21 inches above the surface of the floor, and was surmounted by a circular piece of York stone. The cost of this brickwork, exclusive of the pillar, may be exhibited as follows— BRICKS AND MORTAR FOR THE JOB.
100 red bricks. £ . d.
350 red bricks. 3 5
18 barrow-loads of sand (14 cubic yards). 0 12
45 bags of lime (£3 cubic yards). 0 4
Labour. 4 0
Total. 4 40
We have now to consider the upper (wooden) walls of the observatory. These are formed of upright and horizontal 270 TELESCOPES. timbers, 4 inches square in section. The uprights are 12 in number, tied together at the top, in the middle, and at the bottom. The actual construction consists of 4 frames put together with 8 iron bolts, each bolt being double-headed and joined together by strong bolts with nuts. All the frames are 6 ft. high ; 2 of them are to ft. 8 ins. long and the other 2 (which are the same) are to ft. 10 ins. long. The frames are fastened together, and in their places, the external length of each side of the square is ro ft. 5 ins. Each of the sides is tri- sected by means of the uprights. In the centre third of one side, a window is placed, and on this side, the space between 2 of the other sides is appropriated to a window, whilst the fourth side is covered throughout. As I was not very familiar with the making of the walls, I had some difficulty in making up my mind. In my first Sydenham observatory the walls were weather-boarded, and painted inside and out. Weather-boarding is a perfectly satisfactory method of covering a wall, but it is not so easy to paint as when decided on using galvanised corrugated iron, as much more quickly put up and much cheaper. I considered the possibility of using wood shingles instead of corrugated iron, but found that would be troublesome. In an observatory erected in the Isle of Wight by a relative of mine, and on very much the same principle as mine, they used wooden shingles for covering the uprights and weather-boarding, with the usual grooves and tongues. This also is a perfectly satisfactory covering where time and care cannot be too studied, and where material of good quality can be obtained. But in my case, where all the frames are not covered at all inside, and I think they are best left uncovered. Of course, the effect of covering the frames with wood shingles would be to make them heavier, renders more difficult the problem of keeping the inside and outside temperature of an observatory equable, which is a matter of much importance, to secure the good definition of objects seen through any telescope. A diagram showing how four frames are connected together. Figs. 324-325 PLATE CXVIII. Photograph Equatorial of the Radcliffe Observatory, Oxford. Side-coast Equatorial of the Cambridge Observatory. 320 Fig. 326 PLATE CXIX. A large telescope with a dome above it, and people working around it. 36-Inch Refractor of the Lick Observatory (Warner & Swasey). [27] FURTHER DETAILS. 271 UPPER WALLS.
Timber frame-work, door, 2 windows 8 to 10
Lock and sundry fittings 0 to 9
Framing for corrugated iron (6' x 2') 1 to 3
Ladders for taking the wall-work 1 to 4
The entrance-door is on the N. side, and there are windows on the E. and W. sides. These supply adequate light, and may be regarded as away from what is normally the windward or stormy points of the compass, so far at least as the South window is concerned. The windows are of the ordinary square, open as casements, with hinges on the upper side. Hung in this way, not on the right or left sides, as is usual with casement windows, they afford a good opportunity to allow rain to blow in if it should be known that they have been left open and rain comes on during the observer's absence. Use is made of the transverse tiers of the framework of the wall for shelves, for hanging pictures, etc., for shelves, or as supports for shelves of greater width than the 4 in. of the ties themselves ; but 4 in. is quite sufficient for a shelf of any size. The roof is supported by pillars required inside an observatory, except the larger books and such things as boxes containing eye-pieces, etc. The clock is placed in the S.W. angle of the observatory. It is driven by a very good ordinary regulator, showing, of course, sidereal time, with a secondary dial gradu- ated to 24 hours. It was made by a very first-rate London clock-maker, who had never made one until he made mine under my supervision. It cost £28, and often goes for many weeks with a rate of about a second a day—not bad, for what I may call a merely civilian clock. 272 TELESCOPES. At East Bourne I used to rate it by means of a transit theodolite discant from the Ordnance Survey, and which I therefore had up close at hand. It was a very good transit instrument, or even a substitute for one, as I find it easy enough to convey the time from the Westminster clock every few days by means of a good watch with a second's hand. This was done on several occasions, and I have never I second wrong. The time thus obtained and imparted to my clock after an interval of an hour or two is never sufficiently well known to be of any use. But when we consider that the celestial object by means of the equatorial, my meridian being, it is to be remembered, only by a very little difference W. of Greenwich. Proceeding onwards, and, as a literal fact, upwards in the construction of the observatory, the next and in a certain sense, final matter is the roofing-in, and this is the most difficult part of the whole work. In order to make a roof over revolving top (commonly called a dome), though in small ob- servatories it is seldom such), the plan of which is a circle, or a rectangle, or square, or octagon, etc., it is necessary to have on the top of the square of walls. It is in effect a circle inscribed in a square, to use the language of geometry, which has to be dealt with, and it is evident that the circle must be so placed that it has a bearing on all four sides of the straight sides of the square, which means, of course, that the 4 corners of the square obtain no cover from the domed roof. In order to obtain as stable a bearing for the dome as possible, the angles of the wall frames are tied by substantial pieces of timber to each other, so that they form a solid block quite regular octagon. If this conversion is judiciously carried out by the joiner the effect is that the revolving dome is pro- vided with a substantial bearing which is practically circular and continuous. The cameras mentioned above as exposed to 'the sky have FURTHER DETAILS. 273 to be filled in with a water-tight roof. This is best done by providing a transverse ceiling at each corner of match-boarded walls, which shall be turned up to meet against the channel plate (to be described presently), and turned down over the edge of the walls to an extent sufficient to prevent rain being driven into the building. The roof may be made of any material of general suffice, unless the building is in a very exposed situa- tion. I have used lead, and recommend it because it is, of course, water-tight if put on by a competent plumber, and can be removed when necessary without being removed from the locality. It is true that lead is expensive, and cheaper materials may be employed, such as sheet-zein, tarred felt, and paint, but these materials will not stand the test of time. Lead roofs can never be removed for use for a second time, and the last named are not only perishable in a general sense, but are difficult to repair. Here it may be remarked that an eaves-gutter to carry off the rain which falls on the roof may perhaps be deemed by some persons to be desirable, but this is a remembrance which I have no occasion to bear in mind. The eaves-gutter must run from roofs downwards more or less clear of the walls to the concrete footings of the brick wall outside the building; whence it finds its way, by gravitation, to an ordinary storm-water pipe within some 6 feet below the level on which the observa- tory is built. FLAT PART OF ROOF. The cost of the flat roofing at the corners just described was as follows:
60 ft. run of 6-in. match boarding L 1
Lumber (timber) O 7
7 sq. ft. of 3-in. lead O 19
Lumber (plumbum) O 2
Nails, screws, and other materials O 16
Total 472
A page from a technical manual or report discussing the construction of an observatory. 274 TELESCOPES. THE DOME. We now come to the most troublesome feature in every observatory—the construction and movement of the dome. On the top of the 4 walls and on the continuous bearing already mentioned there is fixed a circular wall-plate, as it is called, which is made of cast iron, and is divided into four pieces together about 2 ft. in length, so that when they are all fitted together they shall make a ring 8 ft. 8 in. in its internal diameter, and 30 ft. in circumference. The rim is 4 in. On the top of this are fixed segments of a circle, 9 in number, of cast-iron, slightly hollowed in the middle, with a rim 14 in. high on the outside, and 12 in. high on the inside. These form a kind of circular tramway, in which 3 or more iron spheres or old-fashioned cannon-balls, about 4 in. in diameter, run. These perpendicularly through the holes in the plates. I have only 3 such balls for the 10-ft. dome, but 4, or even 5, might perhaps be better. They would, however, only be better if they were all very truly identical in diameter and depth of bore; but these could not be made in simple cast-iron; they would have to be turned to a given diameter in a lathe by a competent workman, which would involve a great deal of time and trouble. In fact, I think that even casting, Yet, unless they were true spheres and of identical diameter to a nicety, they would be useless for distributing the weight of the dome over the additional points of bearing beyond that bearing afforded by the 3 balls with which one started. It would also added that even 3 balls have to get together, however carefully they may have been started with an angular interval between them of $120^\circ$. I find it a good plan to mark on the dome itself inside, or on the circular wall-plate, points which are $120^\circ$ apart, and now and again to bring a ball up to one of these marks, and then see how FIO. 327 PLATE CXX. A large telescope inside a dome. The telescope is mounted on a rotating mount with various mechanical components visible. The interior of the dome is visible, showing a spiral staircase and some windows. 36-inch Refractor of the Lick Observatory (Warner & Swasey). 224 FIO. 328 PLATE CXXL Eye-end of the Lick Refractor. [2714] Fig. 329 PLATE CXXIL Distant View of the Lick Observatory from the E. (H. E. Mather). 72481 FIG. 330 PLATE CXXIII. The DuSable Observatory, Chicago University. 1475 THE ROOF OF THE OBSERVATORY. 275 far the other 2 balls have got away from what should be their marks. When the displacement has become considerable it should be prevented by means of a ball (or a lever), such as a piece of quartering), so as to free the 3 displaced balls, which can then be moved backwards or forwards to their proper positions. It is obvious that this operation may easily disturb the balance, since the interval between 2 of them has become as much as 160° or 180°, a very great strain is put upon the dome, which will tend to overbalance itself, and come down on its side. This difficulty is removed by making the roof movable at all, even under the most powerful manual pressure. The construction of the dome is the most difficult, and indeed the most expensive part of the whole work. The first thing to do was, first of all, to start with a cell, on which the roof has afterwards to be built up. It is absolutely necessary that this cell should be very strong and rigid, because it has not only to sustain the weight of the dome, but also to transmit to it all the strains set up by the strain due to the fact that the whole of the superincumbent weight rests on 3 points (z.e. balls), and, moreover, is subject to a constant oscillation about each time that the dome is pushed round on its ball Bearings. When the diameter of the cell is no more than about 8 ft. the cell may be made of 5 or 6 layers of i-in. boarding, and covered with sheet-iron plates. The ends of each one of the 5 or 6 rings thus supported breaking joint with the ring on either side of it, until the desired thickness is arrived at. The outermost ring is then cut out and fitted into a composite ring thus built up a band of sheet-iron may be fastened by way of giving further stiffness. The cell being completed I found that it was more than 8 ft. to fit, I had the foundation cell of the dome constructed some-what differently. Instead of its consisting of one ring of 5 or 6 layers of wood in contact, it consists of 2 rings, each of one thickness of stout timber, 4 in. thick, separated from one another by stout upright ties 7 in. long, and secured on the 276 TELESCOPES. upper side and on the lower side by coach-screws countersinks on the lowest run. This gives a very strong and substantial connection to the ring. To the underside of the foundation cell, however it may be constructed, 2 concentric rings of iron are fixed by screws passing through holes in the upper one, and these are for screws into the instrumentum. These rings must be carefully forged, or, better still, be made of rolled iron about i. wide and $\frac{3}{4}$ in. thick. The central point between these 2 rings, which is to be the axis of rotation, must be formed into a hollow channel in the fixed plate (already described) of the main building, must coincide exactly—that is to say, must be circular—so that when the telescope is set up in its place there is this absolute coincidence there will be great and inconvenient friction when the dome comes to be turned round on its ball Bearings. It is this part of the whole observatory which is most important and which gives the greatest difficulty. From the upper side of what I have called the foundation ring rise the rafter's, i4 in number. These do not meet in what is called the "roof" but are placed at various points in a rectangular framework, about 5 ft. by 1 ft. in, the exact size depending in every case upon what is wished to be the diameter of the circle which is to be observed with the telescope. The fourth side of the rectangle is, so to speak, non-existent—that is to say, it is formed by a cross-bar of iron, see edgeways, so as to block as little as possible of the sky when the telescope is set up. This cross-bar is hinged at each end. Two shutters, meeting one another halfway, rise on hinges attached to a adjacent rafter's, which, of course, for that purpose has been made slightly longer than any other rafter's. The frame, which is supported by the rafter's, constitutes a flat roof to the dome. In order that the telescope may be able, on occasions, to be pointed to the zenith, this flat roof is made to open on hinges at the back (i.e. away from the shutters), and is guided up and Fig. 331 PLATE CXXIV. Equatorials under Construction at the Dublin Works, 1912 (Grubb). No. 1 for the Johanningh Observatory ; Object-glass of inches. 270 270 Figs. 332-333 PLATE CXXV. A wooden framework of a revolving telescope with a large lens at the bottom. Simple Wooden Framework of a Revolving Telescope, used by the late Professor James Clerk Maxwell, Edinburgh University. A modern observatory building with a dome roof. The Aubert Observatory, at Leiden, Groningen, Sydenham. 177 THE ROOF OF THE OBSERVATORY. 277 down by having 2 iron quadrants working through iron catchers, motion being imparted by a pair of pulleys hanging through pulleys inside the slope-roof. The flat roof is covered with thin lead, and the hinges are protected by large pieces of leather running all along the back-side, and made, as far as possible, to fit into the grooves of the woodwork. In this arrangement the flat roof, or lid, of the dome (as perhaps it had better be called) may be raised from the horizontal, through 90°, and then lowered again, so much, no wishing to strain the leather covering of the hinges. In order to open the 2 main shutters, the lid has to be raised 3 or 4 in. to get it clear of the shutters. Special provision is made for this purpose, by means of a small door in the roof, rain, or, rather, to allow any rain which gets in to run down. The shutters can be, and often are, arranged on a different plane, either one above the other, or one on top of another. One one to the left ; or the two are replaced by one which may be constructed to slide either to the right or to the left as may be wished. This is done by means of a pair of cast-iron bearings of its own, formed as a framework outside the sloping roof. I have never been called upon to manipulate shutters arranged in this fashion, and therefore cannot speak from personal experience. It would seem that it would be more difficult with such shutters to exclude the rain than with shutters such as I have at Sydenham. At any rate, my lid, which was intended to slide in this way, I had altered at once to its present form. There is yet another form of shutter which has some advan- tages in windy situations. It really consists of two shutters, but they are so arranged that when one is opened outwards left, as just described, it slides up and down ; and when down— that is, open for use, projects downwards, overhanging the case below. If these shutters were not so constructed, and down shutters are to be employed at all, they had better be so arranged as never to uncover more than half the opening 278 TELESCOPES. in a vertical direction. In other words, to open the observatory for use, the upper half of the shutter must slide down over the lower half; or the lower half must slide up behind the upper half. This method of procedure is open to the objection (which in certain temperatures of the atmosphere is very real) that it limits the amount of light which can enter. It also limits some system of weights to counterpoise the shutters when they go up and down ; which weights dangle about inside the observatory, and are liable to become dirty, and thus more or less unavailing. Besides these objections, this system of shutter is much more expensive to construct, and not easy to work in smooth and pleasant working order, so as nothing of the delicate mechanism is seen, and no place the wateright. The question of the material for the roof I have always solved by putting on a lead-boarding, fastened with screws, and well stopped with white lead and painted. When my observatory was re-erected at Sydenham in 1805, after seven years' exposure to weather, two of the three boards had been broken off, the last decayed or damaged so as to need replacement. Two or three boards had been cracked in taking them to pieces at Eastbourne, but these cracks are readily made good by white lead. As regards the rest of the roof, being composed of boards suspected to be insufficiently seasoned, it might be a great precaution to cover them with canvas, well painted on both sides. Willesden canvas, sheet copper, or zinc (without boards), may also be used for the dome. I have heard Willesden canvas well suited for this purpose; but it is not so strong as copper or zinc, nor does it resist the weather for any length of time. The copper or zinc may be of the ordinary roofing thickness, or even thinner. The pieces must be cut into sectors to fit the bays of the dome. Each piece must be secured at the top and bottom, and on cross-battens, with copper or zinc nails; but the sides must be Papier-mâché Dome erected at the Royal Observatory, Cape Town, with opening extending beyond the Zenith (Grubb). Papier-mâché Dome mounted on iron-framed Observatory covered with wood (Grubb). Papier-mâché Dome of 37-ft. diameter, erected at Calton Hill Observatory, Edinburgh (Grubb). PLATE CXXVL Page 334-337 Barcelona University (Grubb). 278 Figs. 338-340 PLATE CXXVII A photograph showing a room with large windows and a door. The door has a sign on it that reads "Café de la Paix." The room appears to be part of a larger building, possibly a hotel or restaurant. Photograph by Paulus. Lecture Illustration. Direct view of the St. Germain-Les-Bains Hotel, as seen from the window of the Café de la Paix. The hotel was built by Gustave Eiffel, the architect who designed the Eiffel Tower, for the World's Fair in Paris in 1889. 179 FURTHER DETAILS OF THE ROOF. 279 counter-lapped (not soldered) in order to allow for expansion by summer heat. Patterns for the sectors must be prepared in brown paper after the frame of the dome has been put together. Dome : Contract price of dome, including iron rings and £ 5. d. iron channel-plates 30 18 11 Laid upon putting same together at Sydenham 19 8 27 18 7 Adding together all the items given previously under their various heads (about £60), it may be taken that the Sydenham observatory will cost about £100. This is a very moderate sum, considering what can be done with it, and how little it is possible, £70, after adding the value of some octectars which I did not have use for to buy specially. The cost of reproduc- ding it is now meant to be merely a matter of raising the price in the private laboratory, but since the dome was built in 1860 ; but, on the other hand, several pounds might be saved in the foundations. This is not meant to be describing what I have, more or less, done myself, or what has been done under my own direct supervision ; but I am prepared to find that many of my present researches would not have been made without the aid of Sydenham, is too solid ; in other words, has been too costly for the purposes of amateurs of moderate means and ambition, though it was far from my intention to spend on it more than I have done. I fear there might be some foundation for this criticism, and, accordingly, I would recommend, as an alternative to my plans, a building similar to that erected by Mr. Berthon at Cambridge. Rev. E. L. Berthon, Vicar of Romsey, the inventor of the now celebrated "Berthon" boat. A description of Mr. Berthon's form of observatory, from his own pen, appeared in *The 280 TELESOPES. English Mechanic of October 13, 1871; and, as a consequence of the publicity acquired in that work and elsewhere, I have learned that a number of structures on the Romney model have been erected in various parts of the United Kingdom. Much which was put up about 20 years ago by the late Mr. T. R. Clapham, of Austwick Hall, near Lancaster, a descrip- tion of which, from his own pen, appears in the second volume of my Handbook of Astronomy. Mr. Clapham was a clever man, and possessed a great deal of practical skill; which, he visited, represented Mr. Berthon's idea, with sundry minor improvements and developments of an advantageous nature. The book contains many interesting descriptions of what Mr. Clapham kindly occupied for me in the pages of the book which I have just mentioned. I am very glad that the foregoing details has been to encourage my readers who possess telescopes which, though in a certain sense portable, are not readily portable, to make them fixtures, and house them in observatories properly fitted up. The most convenient form of telescope is one mounted equatorially mounted on a fixed stand, and protected from the weather, is capable, in careful hands, of yielding more useful and profitable results than any other form. A telescope larger than a larger telescope mounted only on an altazimuth stand which has to be carried in and out of a dwelling-house on every occasion that it is used, is not always easy to find such objects as these when they are required for use on an astronomical career. To all such I would simply say that I am giving expression to the experience of half a century during which I have had opportunity to test the apertures of 13 inches (unmounted), 3 inches (mounted on an equatorial block without circles), 4 inches (mounted equatorially in an observatory) and 6 inches (in a box). Perhaps this is the most conclusive evidence for the type of lens which we now in mind is that of spending all their available money in improving Figs. 341-343 PLATE CXXVIII. Sir W. Peck's Observatory, Rousden, Devonshire. Mr. J. Tebbutt's Observatory, Windsor, N.S.W. Fig. 343 PLATE CXXIX. The Imperial Observatory, Vienna. 184 THE TREPTOW OBSERVATORY. 281 ing the aperture of their instrument, and in regarding its stand and its house as minor matters. This is a very grave mistake, since the equatorial mounting is the most important part of an equatorial mounting; however rough, with circles however coarse in their graduations, contrasted with an altazimuth mounting, however smooth and delicately made, is great: it means the difference between a telescope which can be used quickly and easily, with ease, or 2 or 3 hours' work in hunting for and studying half a dozen objects with trouble and difficulty. The present system of revolving equatorials with detachable telescope-tubes whose motion is to keep the tubes in boxes in their houses, and have equatorial stands in the open air in their gardens covering them, is a very bad one. It is not only in keeping the tubes out of the house and back again as was required; but, however unavoidable in view of particular circumstances this system is worse than any other one which will be found conducive to good work or much work. Fig. 344 is a view of a telescope of entirely novel construction. The tube itself has been built up by being erected near Berlin by an enterprising German astronomer, Dr. Archenhold, in spite of much hostile criticism on the part of German men of science. The problem to be solved was how to construct a telescope that would be both convenient and inconvenienced by a very bulky and unhandy stand covered by an enormous dome expensive to construct and laborious to move about. The answer was to make the telescope tube itself so long that it could be moved about without taking down the tube. A tube 50 feet or more long is very great, especially when it is a question of observing at one time objects low down towards the horizon, or high up towards the zenith. This difficulty nowadays is met in large observatories, constructed regardless of expense, by surrounding the main pier of an equatorial with a travelling wall, which can be raised or lowered at the pleasure of the observer. Such a system is illustrated elsewhere (see Figs. 236-245 and). By means 282 TELESCOPES. of such a floor the observer can put his seat in any position which suits him, but the time and labour involved in bringing about the necessary alterations to the structure of Archenhold's has been able to arrange to keep the eye-piece near the centre of motion by swinging the telescope tube in a great fork, which, provided with suitable bearings, will allow the tube being run up into its case as may be required, whilst the other parts are placed on a solid concrete foundation, which secures due stability coupled with great compactness. In this way a structure not expensive or difficult to build, because of no considerable size, whilst the telescope tube, when not in use, is brought out of doors and protected against all kinds of weather by a cheap portable roof, which is made to run on it or off it as required. The result of fitting up the instrument in this fashion has been to make it extremely convenient for both finder and comparator, and the whole instrument with its pre- tending roof, has cost no more than about £1300, of which £2300 went in the object-glass, which is said to be an excellent one. It is hoped that this instrument will be used for some years, and it will be interesting to watch the future history of this novel construction, which was only finished and brought into use in April 1909. PLATE CXXX. Telescope at the Trepow Observatory, Berlin. 4-ft. Reflector of the Melbourne Observatory. Figs. 346-347 PLATE CXXXXI 28-inch. Refractor of the Greenwich Observatory. In use for visual work. Meridian Circle, U.S. Naval Observatory, Washington. CHAPTER XV. TIME AND ITS MEASUREMENT. Years—Months—Weeks—Days—Hours—The Sidereal year—the Mean Solar Year—the Calendar and the return of its undergone—By Julian Calendar—The Gregorian Calendar—The Solar Day—The Lunar Month—The Week—Quotation from Lepage-Savant—The Lunar Time—The Day—from 6 a.m. and p.m.—Rising time—Time—The Prime Meridian—Greenwich—The Equinoxes—The Solstices—Different Nations—Where does the day begin?—The Transit Instrument—and how to use it for obtaining the time. "TEMPUS FUGIT" is a truism which affects us all, from babyhood to old age. The human character which, on its historical side, has many fascinating features— At the "Time" and its Measurement " might readily seem a good lesson for the schoolboy, but rather the utilitarian side. The subject will be most conveniently approached by posing certain questions to be used as pegs on which to hang such information as it is intended to give. Let us consider the following questions— 1. What is a year? 2. What is a month? 3. What is a day? 4. What is a day? 5. What is an hour? 6. Where does time begin and end? 7. How long is a day? 8. Who starts and runs the almanac? 49 284 TIME AND ITS MEASUREMENT. All these questions may be said, at the first glance, to have a very commonplace appearance, and the science which lies behind them is not of a very obvious nature. But these questions, when properly handled, admit of some simplicity and ease, as might at first sight appear. What is a year? The answer is the time occupied by the Earth in making its complete journey round the Sun. This answer seems sufficiently simple, but it is not so in reality, because we have to consider where the Earth starts from, and also what is meant by "journey." We must take into account that one "year" is the interval, simplifier, is the interval which elapses between two successive passages of the Sun through the same equinoxes. It is this interval which we call a year. It begins from the moment when the Sun leaves a fixed star until it returns to it again. This kind of year constitutes the "sideral year," and in our current notation consists of 365 d. 5 h. 9 m. If we suppose that the Earth has no retrograde motion, but possesses of a small retrograde motion from E to W, which is constantly in progress, and the result of which is that the Earth does not return to its starting point until it started before it gets round to the Star from which it is supposed to have started. The difference of time is a little more than 20 minutes. (The "mean solar year" is 20 minutes shorter than the year measured by the stars, or sidereal year.) Length of the mean solar year is therefore 365 d. 5 h. 48 m., neglecting fractions, and is therefore nearly equal to the "solar year," for astronomical conversation and in almanacs prepared for terrestrial purposes. Besides this, astronomers take note of the "anomalous year," which differs from the mean solar year by about 7 hours upon the rather abstract fact of the line of apsides of the Earth's orbit being subject to a progressive motion in virtue of which the time between the Earth passing one perihelion and another differs from both the mean solar year and the sidereal year. A diagram showing the Earth's orbit around the Sun with lines indicating different positions over a period of time. WEEKS AND YEARS. 285 The month and the week depend more directly upon the Moon than upon the Sun for their basis, as we do not speak of a solar month or a solar week, but only of the lunar month of 30 days, which is of very ancient origin, having been handed down to us from a remote period when the Sun was held to be the chief deity. The week has no fixed number of even pace, with 3 days allotted to each span; but, as this supposition is at variance with the fact, it was soon found that, to treat the year as consisting of 12 months of 30 days each, or 360 days in all, would be too long for the purposes of civil reckoning in difficulties. Hence arose the necessity of putting on an odd period of several days to secure some sort of uniformity between the years. This was done by adding one day to every 12th (or 12th) movement of the Earth round the Sun), and the year as adopted for the purposes of civil reckoning. When an adjust- ment had been made in this way, it was found that, beginning with the addition of 1 day to the year, one of which was allotted to certain of the 12 months. Then it was discovered, and this discovery was confirmed by many other observations, though, and that it ought to be 54 days. Next it was found that the period of 54 days was several minutes too much, and that 1 h. 55 m. was nearer the mark. This discovery was due to the great Greek mathematician Archimedes. It is in the highest degree creditable to him that he arrived at a value so very near the truth, for the best modern results have been obtained only by him; but by accident. This state- ment does not exhaust the history of this very tangled subject. Julius Caesar was the man who may be said to have started our calendar nearly in its modern form. He could not, of course, have known what he was doing; but he did know that there was a discrepancy already mentioned was an exact quarter of a day, and would be cured by dropping in a whole day every four years. The idea was plausible, and it answered its pur- pose. The Julian calendar is still used occasionally, or the fifth day before the Kalends of March (the Roman Notation) remained fixed. The following table shows how many days are contained in each month according to this system:
Month Number of Days
January 31
February 28
March 31
April 30
May 31
June 30
July 31
August 31
September 30
October 31
November 30
December 31
This table shows that there are 365 days in a common year and 366 in a leap year. 286 TIME AND ITS MEASUREMENT. pose for a long while, but by the middle of the 16th century things had gone astray again, so that the year began 10 days later than it ought to have done, and the day of the year, namely March 21. This was the origin of what we call the Gregorian reform of the calendar, which took its name from Pope Gregory XIII., who issued it in 1582. He necessarily imposed his suggestion on the States of Europe of the Roman Obedience, but the Protestant States and the Greek Church did not follow suit. In England the new style was introduced in 1752, when all the old dates from 1752 to 1753, and all 11 days were ordered to be dropped out of the English chronology at that epoch. This enactment caused a good deal of annoyance among those who had been accustomed to use the Julian calendar, and in many places in English history we find double dates, marked O.S. (old style) and N.S. (new style), and why the national finances are still affected by this anomaly. Even to this day the Greek Church sticks to the old Julian calendar, and the discrepancy between the two styles has grown up to 13 days. Various proposals for reform have been propounded, some of them of great exactness, for rendering more scientifically exact the Gregorian Calendar, with its arrangement of leap years and so on. But even if we could devise a method for inserting an extra day in the course of several thousand years, no useful purpose would be served by dwelling on any of these proposals in this place. The number of days in a year, or 365 days, must be mentioned, not that it has any great bearing upon our daily affairs except as regards a calendar of the high and low tides of the ocean--a matter which comes home to teachers on the sea-coast. We must now say something about the "week," which is a unit of time of the widest application. Its origin is antiquity, and though it is usual to regard it as one-fourth portion of the lunar month, it is impossible to doubt that, after TIME BY THE MOON. 287 all said and done, it is a memorial of the creation of the world, and therefore in use for nearly 6000 years. Laplace's observations show that the Moon has been in motion ever from the very highest antiquity, in which its origin is lost, has, without interruption, run on through ages uniting itself with the successive calendars of different nations. . . It is, perhaps, the most remarkable fact in the history of human intelligence, and appears to indicate that all such intelligence came from one common source—whence, Laplace might have said—"the Moon." The part played by the Moon in the computation of time must not be too lightly esteemed because, from the earliest ages and among the most uncivilised nations, the phases of the Moon, beginning with the first appearance of the New Moon, furnish a chronological scale accessible to everybody and easily utilised. Hence we find that even in our own times, when we speak of days, months, years, we should speak of as many months or years, by saying that such and such a thing happened so many "Moons" ago. This is true only because every year begins with a new Moon. Whenever this happened, they have seen the Moon wax and wane so many times. It is easy to see that, if a canoe was upstated on the day that the young Moon was first seen, and that a young man saw his wife on her wedding-day is it not possible that "Moon," an interval which might be indicated in days if, since the accident, every sunrise or sunset had been noted by means of some instrument? Even this method of computing intervals of time has been used for instance, by shipwrecked crews. It is evident that at some time in the "day" this. This, of course, is universal use all over the world by everybody for every conceivable purpose, but here again the insoluble problem comes before us. Who invented the idea of dividing Bishop Christopher Wordsworth, in his Commentary on Genesis, has some interesting remarks which deserve attention. 283 TIME AND ITS MEASUREMENT. the day into 24 hours, or the alternative reckoning of 12 hours of day and 12 hours of night. Here are questions which cannot be answered off-hand, and which in a certain sense are unprofitable questions. Hipparchus seems to have divided the day into two equal portions of 12 hours each, beginning one of his divisions at midnight, and the other at noon. It is clear whether this was his own original idea or whether it was borrowed from somebody else. So many systems were for- mulated by ancient astronomers, that it would be tedious to give all the hours, that it would be monotonous to attempt to describe them. Suffice it to say, generally, that whilst the total of 24 was in general use, there have been great varieties of practi- tioners who have adopted different methods of dividing the hours. While some started from sunrise, others started from sunset. While some started from midday, others started from midnight. Some grouped the hours into pairs, others into triads, some even into groups of four, while others, grouping the hours into triplets or quadruplets, which last-named system still prevails on board ship under the navigation laws. Even the present generation of inhabitants of the Earth have seen, or are seeing, some momentous changes, two in particular which may be said to be not remotely connected with the intro- duction of railways. For instance, in our modern motor vehicles, or on foot, there would never be much confusion between a.m. (ante-midday) and p.m. (post-midday) because, as a rule, we start our journeys in the morning and end them begin anything extending into the small hours of the morning. When, however, long main lines of railway, covering hundreds or even thousands of miles become available for travel, the question arises as to what time of remaining will become serious, and the a.m.s and p.m.s of our forefathers became very ensnaring. The English railways, in that conserva- tive country where they have been most successfully developed and admired, have met the difficulty by various shifts, none of which can be pronounced satisfactory. Whilst one line uses THE DIVISION OF DAYS INTO HOURS. 289 light-faced figures for times between 6 a.m. and 6 p.m., and black figures for the times between 6 p.m. and 6 a.m., another line being drawn same sort of figure at all the other convenient with itself a same point, and leave it to the passenger to find his way through the time-table as best he can. A third line, keeping to the same sort of figures, indicates time by hours only, and leaves out the minute and second figures. These expedients are all very lame and unsatisfactory. Certain foreign nations have done more than this, but they have done so by making the only proper scale, and timing their trains from o'clock to o'clock at 4 o'clock. Without doubt this is what, sooner or later, we shall come to in England, following, for instance, the Italians, and the Germans. But I am afraid that we shall never be able to only adopted the 24-hour day for railway purposes, but for every purpose. The second modern change in the computation of time alluded to above has reference to what is called the "prime meridian," or zero for time on the Earth. Formerly every nation had its own prime meridian, or some such equivalent fixed point of longitude. Thus, time in Great Britain was reckoned from the Greenwich meridian; in Ireland from Dublin; in France from Paris; in Spain from Madrid; in Italy from Rome; in Germany from Berlin. In this way, say, from Spain into Germany, would start with his watch showing Madrid time. When he entered France he would have to change his watch to Paris time; when he reached Germany he would have to change it again to Berlin time. When he quitted the eastern frontier of France his watch, regulated by Paris time, would be no good for German railways until he had changed it once more. It is clear that this state of things have probably been experienced by many readers of these pages, but they are diminishing, and in the near future will practically cease to exist because the whole world is learning the advantage of having only one prime meridian for the whole world. By common consent, the 10 290 TIME AND ITS MEASUREMENT. meridian of Greenwich has been selected as the prime meridian of the world, with provision for local adjustments to meet the facts of each country. This adjustment is made by means of which it cannot, therefore, always be noon or midnight at every place on the Earth's surface at the same absolute moment of time. What those adjustments are we have now to consider in a summary form. The following table will give a clear idea of such publications as Whittaker's Almanac. It has been agreed by various nations that they shall take their local mean solar times at the instances of only whole hours, so that our ideal traveller from Spain to Germany will never have to alter the minutes and seconds of his watch, but only to remove them when he gets into Germany. In Austria, the official hour will be one hour in advance of Greenwich; in Turkey and Egypt 2 hours in advance, and so on. On the other hand, when he goes to America he will find that the official time is two hours behind New York. Thus, when the time is spoken of as "Eastern Time", the word "eastern" having reference to the position of New York with respect to Greenwich, it follows that all places west of New York on the American continent, he will come upon three other "times"—namely, "Central," "Mountain," and "Pacific" times, which are respectively 6, 7 and 8 hours behind Greenwich time, while those on the Pacific coast are 12 hours behind. There are 4 hours slow of Greenwich. This system of nomenclature, depending on Greenwich, is not limited to the Northern Hemisphere; indeed, many countries in South America similarly adopted the Greenwich meridian. Some of these have split the hours and taken the intermediate 4-hour as the base-line for their local time. It was this movement for standardising local times when I state that in Victoria, New South Wales, and Queensland local times are linked to 10 hours fast of Greenwich, whilst South Australia has chosen 9 hours, and New Zealand 11½ hours fast of Greenwich for their respective bases. TIME ALL OVER THE WORLD. 291 The annexed diagram, which is published here by the kindness of the Society for the Propagation of the Gospel, though it A circular diagram showing time zones around the world. The center is labeled "Greenwich Mean Time" (GMT). The outer ring shows the 24-hour clock with each hour marked by a line. The inner ring shows the time zones, with each zone marked by a line. The lines are labeled with the names of countries and cities within each zone. The lines are colored to represent different time zones. Fig. 348.—Time all over the world (by permission of the S.P.G.). is not actually graduated according to the official nomenclature dependent on hours in advance of or behind the Greenwich meridian, will yet serve the useful purpose of informing 292 TIME AND ITS MEASUREMENT. readers what are the local times relatively to Greenwich of the countries which are named. The time of day is given through France and North-West Africa, and at Accra, on the Gold Coast, there is a certain hour of which it is said that the Greenwich meridian cuts through it exactly within 1/40th of a second. The writer of the article on the S.P.G. says that this which is so close a passage is borrowed playfully remarks that — "There is one place in the world, in the middle of the Atlantic Ocean, where the time does not go wrong," wrote the Editor of "The Times" from New Zealand to South America, when, on Sunday evening, as he had finished holding services for his wife's birthday, he was told by his friend that the next day would also be Sunday, the same day of the month. He did not, however, hold any more services, but the week of the month passed without any change being made. As long as it continued during the whole time, it seemed a very long week." This allusion to what always happens when a ship passes the 180th meridian from Greenwich, deserves some elucidation, and an account of how it happened will be here narrated. Mr. C. O. Burge, a retired Civil Engineer, writes: "Just before arriving in New Zealand we had to cross the meridian 180° West and East, the antipodes of longitude, and thus we found ourselves in a strange position. We lost one day—that is to say, to go directly from Saturday to Monday ; but we were not allowed to make up for this loss on Sunday, and it would have been lost if, to use an expression appropriate to my nationality, the omission had been celebrated on Monday. I am sure that no one would have thought us mad. All of us, therefore, who did not return in the reverse direction during our stay in New Zealand, must have been aware of the extended days of our return to the old country, possibly years later, while those who remained in the Antipodes never got over their disappointment. It was only last year that we had a sort of true Leap Year, for we jumped over a day—missing "Syllable of recorded time." A page from a book with text about time zones and leap years. WHEN THE DAY BEGINS. 293 " In the case of voyages in the opposite direction—that is to say, eastwards across this meridian—an extra day must be introduced into the calendar. Thus, when a steamer left the port of St. Ives, Ireland, which he wasn't at all, as he would say, being born on the ocean, was launched into this part of the continent on the 20th of February, 1875, and reached Leith, where the ship in which his mother was a passenger was crossing the i8o° line of longitude on the 21st of February, 1875, so that he had been in the same latitude for two days and one night, but only one day and one night according to the calendar. So, though he lived to a great age, he never had a subsequent birthday. This chapter may include the asking of, and the trying to answer, a very tricky question. "Where does any given day, say, New Year's Day, begin?" The most definite answer which can be given seems to be that it begins at midnight at the natural point on the earth's surface which have the longitude of Greenwich as their zero longitude, their day must be regarded as commencing at the longitude of 180° E., and that accordingly as soon as they cross this line they enter a new day. This begins, place by place, on the surface of the Earth as the E. longitude diminishes from 180° down to no longitude at all, while the W. longitude increases from 180° up to 360°. As the 180° degree of E. longitude passes through a point in the Northern Hemisphere in Eastern Siberia and in the Southern Hemisphere slightly to the E. of New Zealand, there will be a difference between these two places. As for people in the Northern Hemisphere, whose longitude standard is Greenwich, may be said to depend on Eastern Siberia, and for those in the Southern Hemisphere under corresponding circumstances may be said to have their day start from near the eastern coast of New Zealand. C. G. Burge, *Adventures of a Civil Engineer*, p. 341. London, 1906. The reason for this is that, because practically the line of demarcation is treated as passing between Behring's Straits, and all Siberia as having East longitude for time purposes.
When the day begins. 293
TIME AND ITS MEASUREMENT. The foregoing pages may suffice for furnishing some ele- mentary ideas on the general principles which underlie the measurement of time from the standpoint of one who regards the matter in its immediate bearings on the daily affairs of life; but the real deal must be made with the astronomical substance of Time, which would be deemed at all exhausted. It would be necessary to tell the reader how the astronomical facts which control our measurement of time are brought down from the heavens to earth, and how they are applied so that everything is tabulated to form the basis, first of our calendar, and then of our almanacs—but all these things would take us too far into the realm of mathematics. In the chapter on the telescope¹ I have named all the equipment necessary for the ordinary purposes of an amateur observer, and we now go beyond this to consider the clock and the clock, and the battery and both these, is one accessory instrument which he will find very useful, namely, the transit instrument for keeping his clock correct without having to attend to it every day, or even every few days, and then having in each case to convert the civil mean time into sidereal time. The principal transit instrument is very simple, and the practical use of it is not at all difficult or troublesome; so much so that remote country districts, away from towns and railway-stations, one occasionally comes upon a non-scientific collector who has a transit instrument, though he does not know what it is, has and uses a transit instrument of some sort for mere time- keeping purposes. The principle of the instrument is this: that every star crosses the meridian of a given place at a definite time, as laid down in the Nautical Almanac; and if, and instrumental means are at command for determining the exact moment when a star crosses the meridian, then by adding (or subtracting) (or some sufficient allowance) also at command, the time is inme- Chapter XIV,, ante A diagram showing a transit instrument with a telescope mounted on top. THE TRANSIT INSTRUMENT. 295 diately obtainable. The accuracy of the result will depend upon the precision of the instrument used and the care which is exercised. Accordingly a large and carefully adjusted transit instrument will give a more accurate result than one which is small and only roughly adjusted. And such an instru- ment will give a better result than no instru- ment at all, for the time of the meridian passage of a star can be ascertained by such a thing as a wall running transversely to the arrival of the star coming up from the E., or the line of the wall. The Transit Instrument for obtaining the time. Fig. 349.—The Transit Instrument for obtaining the time. 296 TIME AND ITS MEASUREMENT. being noted by a clock, or even a watch with a seconds hand. In all such cases the principle is simply this: the almanac says that the star ought to arrive at the meridian at a certain instant marked by the time expressed in hours, minutes, and seconds. If the star arrives too early, the telescope is too close; or the watch is too slow. If the star should arrive after its appointed time the clock or watch is too fast. In carrying out observations according as just described the observer will have to take different times at different stars in order to find when the star ought to appear; and he will also have to convert mean solar time into sidereal time when he wants to know what hour of R.A. is on the meridian at a given moment. The ordinary small or "Portable Transit Instrument" *ex- tends* (fig. 340) so far as to allow of being set up without difficulty by looking at the illustration (fig. 340). There are (1) the telescope; (2) the stand on which it is mounted; (3) the main piece of iron work called the frame; (4) a part, which are connected by a centre-piece, a cube in shape. Into the centre-piece, at right angles to the main tube, are fitted a branch tubes usually conical, which together form the horizontal axis of rotation of the instrument. The transverse tubes are accurately ground to form 2 perfect equal cylinders or pivots. These pivots rest on Y's which are again ground to fit perfectly into X's which support the instrument as a whole. One of the Y's is fixed in a horizontal groove, so that by means of a screw a small azi- muth motion may be imparted to the tubes as a whole which can be raised or lowered by means of two long screws and screws which go through the base are available for raising or lowering the entire instrument so as to make sure that the base is level. This is done by having two holes in each end of one of the Y's and two holes in each end of one of the X's. At one end of this horizontal axis a graduated circle is fixed, which is so that be knowing where the telescope can be set to THE USE OF THE TRANSIT INSTRUMENT. 297 stars of any given declination. This circle is divided into degrees and subdivisions of a degree to be read, with great accuracy, by means of a telescope. The line of the opposite end of the horizontal axis provision is made to receive light coming from a lamp, and designed to illuminate the wires which are fixed in the eye-piece of the telescope. The light reflected up the telescope to the eye-piece by means of a diagonal reflector fixed in the tube. A movable striding level runs parallel to the horizontal axis. To be used to ensure the hori- zontality of the horizontal axis. The instrument should be furnished with a sliding dia- phragm to admit much or little light according as the star be above or below the horizon. A small one likely to be overcome too much light is admitted. A transit is a simple transit instrument, so far as its special features have already been de- scribed. In order that it may order, the climax of its success depends upon the wires which appear in the field of view when the instrument is open for use (Fig. 350). When no vertical wire is required, because, supposing the instrument is in proper adjustment when the telescope is moved up and down, that one vertical wire travels in a straight line through the center of the field of view. It is very often found in practice that an observer watching a star crossing one wire is more likely to make a trifling mistake in estimating the right moment by the clock than if he noted at some time both wires and their positions. It is usual, therefore, to provide vertical wires, the calculation of an average from A diagram showing two stars on either side of a central crosshair, with a crescent moon symbol above them. Fig. 350.—The Planet Venus and a Star as seen in a Transit Instrument. 208 TIME AND ITS MEASUREMENT. which is easy. While it must be stated that 3 wives are better than 1, but not so good as 5; yet, 6 are better than either 3 or 5, and are provided in the large Transit Circles used in the great public observatories. The transit circle must instrument one horizontal wire which serves to subdivide the field of view horizontally, and to indicate the place where the star may be expected to cross the meridian. This wire is usually inclined at an angle approximately equal to the tabular declination of the star; but the horizontal wire has no direct connection with the results yielded as regards the time. It need hardly be stated that the accuracy of the ultra- marginal observations depends upon the exactness with which it is accurately adjusted to its work, and this means that when moved up and down it should always be in the meridian; that when moved left and right it should always be in the plane of the object should both be in focus at the same time; that the centre wire should be exactly in the optical axis of the tele- scope; and that the main tube should be truly at right angles to the optical axis. These conditions can only be fulfilled by means of suitable adjustment screws, which need not be more particularly described here. Fig. 37 represents graphically a thing which is not very generally understood—the "Equation of Time": it is true, and why it should exist, or be required to be acted upon. The explanation is really very simple. We talk roughly of day and night as being due to the rotation on its axis of the meridian every day, or really on the rotation of the Earth on its axis—and such is the case, broadly stated; but the day varies slightly from year to year, owing to the difference between sidereal day by an amount (§§ 95-96) which, though trifling, will disturb the even course of events unless adjusted somehow, and the equation of time, as it is called, supplies the means of adjusting them. *See for such details my Handbook of Astronomy, vol. ii., "Astronomical Instruments," and other books of like nature.* A diagram showing a transit circle with a horizontal wire dividing the field into two halves. The wire is inclined at an angle approximately equal to the tabular declination of a star. THE EQUATION OF TIME. 209 the fact that the Earth's orbit is not being a circle, but an ellipse, the Earth's pace in moving round the Sun (or the apparent daily motion of the Sun through the zodiac) is not uniform, but is faster with the Sun in perigee in January than it is with the Sun in apogee in July. Hence it follows that, to keep an average day constant, we must equalise in some way the irregular length of the different solar day, and the Equation of Time is the expedient adopted. I have never seen the actual circumstances involved in the measurement of time and the differences of time resulting from the Earth's rotation on its axis so graphically expressed as they are in this diagram. It is taken from an excellent monthly penny magazine called *The Cotter*, published by the Religious Tract Society. The whole article is Diagram to represent graphically the Equation of Time. Fig. 351.--Diagram to represent graphically the Equation of Time.
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352/353/354/355/356/357/358/359/360/361/362/363/364/365/366/367/368/369/370/371/372/373/374/375/376/377/378/379/380/381/382/383/384/385/386/387/388/389/390/391/392/393/394/395/396/397/398/399/400/401/402/403/404/405/406/407/408/409/410/411/412/413/414/415/416/417/418/419/420/421/422/423/424/425/426/427/428/429/430/431/432/> Page 2 of 2 (of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2) (Page 2 of 2)301 302 THE SPECTROSCOPE ASTRONOMICALLY. A certain Grimaldi was one of the first to study the prism scientifically, and he did so with much care and success. He made use of a short, but a deep, room through which he let in a ray of light, which he submitted to the action of his prism. He was thus enabled to break up his ray of light, which came from the Sun, and so obtain the solar spectrum, which is composed of seven colours. In this experi- ment, he proceeded to transmit rays of sunlight through glass spheres filled with water. This enabled him to propose an explanation of the phenomena observed by Newton. Grimaldi's modes operandi, reproduci- torially, was the basis of all those engravings, showing how a ray of simple white light is split up into colours, which are found in the spectrum. It seems hardly necessary to dwell on the details of this, though perhaps I had better do so. The ray of light entering a prism is refracted at its two ends, and is bent inwards, and, passing through it, comes out on the opposite side, not as a single ray, as it entered, but split or decomposed (to use the technical term). When it reaches the screen it is broken down into red, orange, yellow, green, end and violet at the other, with many intermediate shades of colour in between. Newton repeated the experiment in different prisms and found that they were all so far improved upon it as to point out that passing the spectrum through a second prism did not cause any further change in its appearance. He then turned his attention to another problem, viz., that of decomposing white light by his friend Arand, of Geneva, in a rough pen-and-ink sketch, to which he prefixed the important legend, "Nec variat ius fracta colorent." (The decomposed light undergoes no change.) This impossibility of decomposing any further a ray which has already traversed one prism constitutes in reality the discovery made by Newton; but he got a step beyond this, for he recomposed white light out of colours by determining the SPECTRUM ANALYSIS HISTORICALLY. 303 proportions in which it was necessary to do this in order to reproduce a light analogous to that of the Sun. He also assigned names to the different colours. Wollaston had been working before any substantial progress was made in this department of Optics. Wollaston was the next man. In looking at a narrow slit of light through a prism, he found that the spectrum was not continuous, showed gaps in the form of black streaks, which divided the spectrum into many compartments. This discovery attracted attention, and remained fruitful ground for Fraunhofer's wishing to determine the composition of refractions of certain sorts of glass which he was using, perceived, and so, to speak, rediscovered what Wollaston had previously discovered. He sketched these black streaks, sketched them, and eventually defined their positions relatively to one another by direct measurement. In conse- quence of his work, it has become known that they are just alluded to are universally known nowadays as "Frain- hofer's Lines," though priority for their discovery rests dis- tinctly with Wollaston. It is necessary to look directly at the slit, and to focus the eye-piece of a telescope on sort to the slit, so as to see the slit very distinctly. The eye-piece must be placed in such a position as to be in the path of the luminous rays, and in the position which answers to that of minimum deviation, the telescope must be brought to bear on the prism, and when the eye-piece is again duly adjusted, a number of lines will be seen in the field of vision. If the prism is a good one, and the telescope is achromatic, a great number of very fine lines will be seen. Fraunhofer observed these lines as he observed by himself certain letters of the alphabet; capitals for some, and small letters for others. These leading lines must be looked for as follows : A in the extreme red; B in the moderate red; C in the reddish-orange; D in the yellow-orange; E and f in the 304 THE SPECTROSCOPE ASTRONOMICALLY. green ; F at the commencement of the blue ; G in the indigo ; H in the violet. These letters, which may be called, are in universal use, but subsidiary letters have been introduced since Fraunhofer's time, and also certain figures for facilitating the comparison of the different parts of the solar spectrum with the lines of other stars. The following table gives the positions of these lines, and it will be seen that they are all situated between 5000 and 7000 A. The lines marked by single letters, such as B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z, etc., are those which are found in the solar spectrum. The lines marked by double letters are those which are found in the spectra of other stars. The lines marked by single figures are those which are found in the spectra of other stars. The lines marked by double figures are those which are found in the spectra of other stars. The lines marked by triple figures are those which are found in the spectra of other stars. The lines marked by quadruple figures are those which are found in the spectra of other stars. The lines marked by quintuple figures are those which are found in the spectra of other stars. The lines marked by sextuple figures are those which are found in the spectra of other stars. The lines marked by septuple figures are those which are found in the spectra of other stars. The lines marked by octuple figures are those which are found in the spectra of other stars. The lines marked by nonuple figures are those which are found in the spectra of other stars. The lines marked by decuple figures are those which are found in the spectra of other stars. The lines marked by undecuple figures are those which are found in the spectra of other stars. The lines marked by dodecuple figures are those which are found in the spectra of other stars. The lines marked by tridecuple figures are those which are found in the spectra of other stars. The lines marked by tetradecuple figures are those which are found in the spectra of other stars. The lines marked by pentadecuple figures are those which are found in the spectra of other stars. The lines marked by hexadecuple figures are those which are found in the spectra of other stars. The lines marked by heptadecuple figures are those which are found in the spectra of other stars. The lines marked by octadecuple figures are those which are found in the spectra of other stars. The lines marked by enneadecuple figures are those which are found in the spectra of other stars. The lines marked by decadecuple figures are those which are found in the spectra of other stars. The letters being understood generally, some details may well now be given which will make their use as an index to the solar spectrum better appreciated. A is a strong line close to the red line ; B is a strong line near to the green line ; C is a strong line near to the blue line ; D is a strong line near to the indigo line ; E is a strong line near to the violet line ; F is a strong line near to the blue line ; G is a strong line near to the indigo line ; H is a strong line near to the violet line ; I is a strong line near to the green line ; J is a strong line near to the blue line ; K is a strong line near to the indigo line ; L is a strong line near to the violet line ; M is a strong line near to the green line ; N is a strong line near to the blue line ; O is a strong line near to the indigo line ; P is a strong line near to the violet line ; Q is a strong line near to the green line ; R is a strong line near to the blue line ; S is a strong line near to the indigo line ; T is a strong line near to the violet line ; U is a strong line near to the green line ; V is a strong line near to the blue line ; W is a strong line near to the indigo line ; X is a strong line near to the violet line ; Y is a strong line near to the green line ; Z is a strong line near to the blue line. The following table gives some particulars respecting these lines :— Very Strong (V.S.)
(This letter has been used for several purposes.)
(It should be noted that this letter has been used for several purposes.)
(It should be noted that this letter has been used for several purposes.)
(It should be noted that this letter has been used for several purposes.)
(It should be noted that this letter has been used for several purposes.)
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Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.Very Strong (V.S.). This Letter Has Been Used For Several Purposes.305 that something lies behind the absence of so many intermediate rays of light, narrow though they be, and slight as may be the joint effect of all these on the spectrum of the Sun on a cursory inspection of it. The story of the history of the successive stages in which knowledge gradually accumulated in the interpretation of these mysterious phenomena is one of great interest. The essential point is this: that various metals and earths in a state of incandescence or combustion, when examined through the prism, exhibit bright lines in the spectrum of light, and that in many cases the distribution of these bright lines is coincident with the presence of dark lines in the spectrum of sunlight. When some of these spectra are carefully compared with the lines in the spectrum of the Sun, and the coincidence of bright lines of known origin with dark lines of unknown origin is established, it becomes evident that the explanation of most of which I do not detail) that the absence of light where the dark lines appear is due to the presence in the Sun of a substance identical with that which produces these bright lines, and which, when examined, found to yield the particular bright line just spoken of, and no other bright lines. The example usually cited to show this is that of sodium. It was found that sodium would be given of the D lines in the solar spectrum. At a later stage in the progress of experiments it was found that, when sodium (or its equivalent, common salt) was heated in a vacuum tube, and its spectrum re-presented in the spectrograph no other prominent lines, bright or dark, than the double D line. Hence physicists came to the conclusion that sodium was one of those substances which is burning perpetually in the Sun. I must cut a long story short by saying that many researches and experiments by various eminent men at various dates and at various places have led to the inference that a large number of metal and mineral substances known on the Earth exist 20 306 THE SPECTROSCOPE ASTRONOMIALLY. on the Sun, and, by suitable treatment by means of spectro- scopes, can be individualised. On the other hand, there are lines in the solar spectrum which cannot be interpreted except on the assumption that there are the Sun substances absent from the Earth, and physicists have long themselves justified in these lines some of the theories and giving them new invented names, such as helium and coronium. In the first instance, and during all the early years of the existence of spectroscopy, the subject was confined chiefly to the Sun, and, though Fraunhofer carried out some experiments on certain conspicuous lines, it cannot be said that the measurements made at that time were of any great scale in other astronomical fields than the Sun until Huggins, in 1864, began his famous researches into the constitution of planets, comets, clusters, and nebulae. The general subject is large. The next matter which should receive attention is the construction in practice of spectro- scopes for actual use in the study of, not simply the Sun, but also other stars. This is a very extensive subject, altogether beyond the scope of this elementary volume. As indeed, the subject of astronomical spectroscopy itself is far too vast to be brought in at the tail-end of a popular book on general astronomy, and is, moreover, a study not likely to be taken up by the reader for whom this volume is more especially intended. It will therefore suffice to confine oneself to two topics which may perhaps induce a few of my readers to wish to go a step further by the aid of books specially dedicated to this subject. The first matter to be mentioned is Secchi's classification of stars. Whilst Huggins, working in conjunction with his friend, Dr. W. A. Miller, of King's College, examined something like too many spectra of about 500 stars, and was led to distribute them into 4 classes or types, an account of which he published FIG. 582.-Secchi's Type of Stellar Spectra. 307 308 THE SPECTROSCOPE ASTRONOMICALLY. in 1868. Secchi's types may be briefly summarised as follows: 1. White stars, of which Sirius and Vega are types, yielding spectra crossed by a broad dark lines, due to hydrogens, much broader than those in the solar spectrum. Sodium and mag- nesium lines are also present in these stars. 2. Yellow stars, such as Aldebaran, Capella, Pollux, Arcturus, and a Cygni, wherein the hydrogen lines are much less con- spicuous than in Type 1, but metallic lines, magnesium especially, are numerous. 3. Stars with exceedingly beautiful spectra, crossed by no or more dark bands, each band very dark and sharp on the violet side of the spectrum, and with a bright line at the centre, Bételgeuse (e Orionis), a Herculis, and Antares (a Scorpii), are the principal stars of this type. 4. Stars with a broad dark bands, shaded in the reverse direction to those of the 3rd type. These 4 types of stellar spectra are generally recognised by spectroscopists as being characteristic of certain star sys- tems, carried out by Vogel, Duméril, Lockyer, and others, led to other classifications. However, Secchi's types have not been generally superseded, though it ought to be added that he himself did not constitute a 5th class of stars showing bright lines in their spectra. The following points may be stated summarily.
Letter Position Strength
A 5800-6200 A Strong
B 5200-5600 A Strong
C 4800-5200 A Strong
D 4400-4800 A Strong
E 4000-4400 A Strong
F 3800-4200 A Strong
G 3600-4000 A Strong
H 3400-3800 A Strong
I 3200-3600 A Strong
J 3150-3250 A Strong
K 3150-3250 A Strong
L 3150-3250 A Strong
M 3150-3250 A Strong
N 3150-3250 A Strong
O 3150-3250 A Strong
P 3150-3250 A Strong
Q 3150-3250 A Strong
R 3150-3250 A Strong
S 3150-3250 A Strong
T 3150-3250 A
Taurus: a Tauri; b Tauri; c Tauri; d Tauri; e Tauri; a Ceti; b Ceti; c Ceti; d Ceti; e Ceti; a Herculis; b Herculis; c Herculis; d Herculis; e Herculis; a Scorpii; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri; e Pegasus; b Scorpii; c Scorpii; d Scorpii; e Scorpii; b Ursae Majoris; c Andromedae; d Tauri;
Stars of the helium type are mainly dis- tributed in the galactic zones: Orion stars are mainly of the helium type, while Canopus is a member of the calcium type. The last matter in connection with stellar spectroscopy, which must be mentioned, is Huggins's interesting and in- genious application of the spectroscope to isolated stars, with the view of determining their velocities of approach and SPECTRUM ANALYSIS APPLIED PRACTICALLY. 309 recession in the line of sight to and from the Sun. Though the whole idea of such an attempt to prove stellar movement by means of spectrum analysis has been abandoned for the time being, yet it does not appear that there are sufficient grounds for distrusting the results arrived at in the case of several dozen stars, though these results require us to talk about miles per second, and even light-years per second, in order to bring us to and from somewhere. CHAPTER XVII. TABLE OF THE CONSTELLATIONS, WITH A BRIEF DESCRIPTIVE ACCOUNT OF EACH. By the entries in the column headed "Centre" it is meant to be inferred that a line of Right Ascension and a line of Declination taken off the map will intercept at a point which may be regarded as the centre of the constellation. Neverthe- ever, is only true of the more compact constellations, for there are some, like Draco, Cetus, and Argo, which are so long and straggling that they have no centre. When, therefore, I state that the constellations are here arranged in the order of R.A., the statement must be regarded as needing some qualification in many cases. In the column of "Declina- tion" means North, and --South.
Name of Constellation. Centres.
R.A. Decl.
Pisces h. 50 -
Sagittarius (Apharatus scutatorii) o 20 + 10
Amebodra o 30 - 35
Phenix o 10 - 48
Cygnus o 10 - 48
Cetus 1 45 - 12
Taurus (Chemica) 2 25 - 33
Bootes 2 40 - 26
Hydrae 2 40 - 78
Perseus 3 20 + 48
360 THE POSITION OF THE CONSTELLATIONS. 311
Name of Constellation. Centra. R.A. Delt.
Homoligium h. m. 3 32
Reticulum (Rhoenoidalis) 3 50 63
Eridanus 3 50 60
Taurus (Bos taurus) 3 48 18
Caelum (Caelus sculptoris) 4 40 42
Sagittarius (Arrows) 5 27 19
Oriion 5 20 5
Sagittarius (Arrows) 5 19 18
Pictor (Pictus pictoris) 5 30 52
Cygnus (Cygnus cygnus) 5 29 14
Columba (Nocchi) 5 40 34
Cassiopeia (Cassiopea) 5 40 70
Lupus (Wolf) 6
Name of Constellation Centres. R.A. Decl.
Virgo h.m. t.
Bolées 13 45 +20
Cygnus 15 00 +40
Lupus 15 30 -70
Lion 15 30 -70
Apus 15 35 +30
Serpens 15 35 +30
Cetus Borealis 15 40 -65
Telugium Amurale 16 00 -80
Lunula Minor 16 00 -49
Norma 16 20 -26
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Aquila Australis: Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis:<br>Aquila Australis: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILA AUSTRALIS: AQUILAAU CONSTITUTIONS: R.A., O.R. O.M. TO 2 H. 25 M. 313 A few lines will now be given to each of these constellations by way of assisting an observer in finding them and in recognising their constituent stars. *Pisces (The Fishes)* is a dull and uninteresting constellation, the principal object of which can only be discovered by classing it upon its form, and then noticing that it is apparently adjoined to the S., the "Square of Pegasus," by means of which it is connected with the latter, so that therefore, it can be readily found. The 2 brightest stars are α Pisces and β Pisces. *Sculptor* is a southern constellation, barely visible in England. Its brightest star, α, is only of mag. 4. *Andromeda* (The Maiden) is one of the largest and most important constellations in the northern heavens, containing as it does stars of the 2nd and 3rd magnitudes (α, β, γ), whilst it is 3½, and v and w are both 3½. *Bootes* (The Herdsman) is a constellation, has the following bright stars: α Bootes, β and γ Bootes, and both β and γ are 3½. *Cassiopeia* ("The Lady in her Chair") is a constellation of great extent, situated in the northern sky. It contains no bright star, but the part of the Milky Way, very rich in stars, runs through it. Its naked-eye stars include the well-known W, group. The chief stars are: α, ω, and β W; and γ W, and ε W, all about 3½. *Cepheus* (The King) is a large constellation situated in his own area, but of no great interest from a naked-eye or telescopic point of view. His most interesting object is the celebrated variable star *Cephei*. The chief stars are: α Cepheus, β Cepheus, γ Cepheus, and δ Cepheus, all about 3½; and ε Cepheus, v Cepheus, all 3½. *Triangulum* (The Triangle). This is one of the ancient constellations, not withoutishing its small size. Its principal stars are β and ζ Triangulum. *Forma Chemica* (The Chemical Furnace). In speaking of \begin{tabular}{l} The most exact evaluations now in use take account of differences of magnitude amongst the larger stars to tenths. These refinements are, however, not necessary when dealing with stars whose magnitudes are given only to quarters of a magnitude. \end{tabular} 314 CONSTITUTIONS : E.A., 2 H. 30 M. TO 5 H. O.M. this constellation it is usual to drop the word "Chemica." It has no brighter star than one of magn. 4½. Aries (The Ram). This is a very bright constellation, there are moderately conspicuous stars which serve to indicate the position of the constellation. These are : a, 2 β, γ, and y, 4. Hydra (The Small Snake). This is a southern constellation not far from the Pole Star. There are : α, 2 β, γ, δ, ε, 2 α, 2 β, and x and y, both about 3. Perseus. This is a very brilliant constellation, because it contains the famous star Aldebaran of the Milky Way. Its stars are : a, z, β, λ, ν, ω, y, all about 3. The star α Persei, better known by its Arabic name of "Alged," is a very remarkable variable star of short period. Hercules (The Lion). A southern constellation, has one fairly conspicuous star, a 3½. Reticulum (The Net) is also a southern constellation. Chief star : β 3½. Eridanus is a very long, straggling constellation, reaching from the Equator to that of S. Declination. Its important stars are invisible in England. They are : a (Acheron), b (I), c (I), d (I), e (I), f (I), g (I), h (I), i (I), j (I), k (I), l (I), m (I), n (I), o (I), p (I), q (I), r (I), s (I), t (I), u (I), v (I), w (I), x (I), y (I), z (I). Taurus (The Bull). This is a large and interesting constella- tion containing many stars and telescopic objects in great variety. Amongst the former are the celebrated groups of the Pleiades and the Hyades and the beautiful 1st-magnitude star Aldebaran. The latter is visible only in the evening sky with a 6½ and Flamsteed's 17 and 27, all of about 4½. Besides these there are no fewer than 88 stars ranging from mag. 4 to 5½. Gemini (The Graving Tool) is a southern small constellation, the two brightest stars of which, α and γ, are only 4½. Dorado (The Sword-fish), a southern constellation, has for its chief stars : α and β. This constellation contains a cele- brated cluster of stars. Fig. 353. PLATE CXXXII. Central Portion of Orion (F. W. Longbottom). 374 Figs. 354-355 PLATE CXXXIII A star chart showing the constellation Orion and its neighborhood. This Constellation Orion and Neighborhood "THE SKY IN LATE" [375] CONSTITUTIONS: R.A., 5 H. 20 M. TO 7 H. O.M. 315 Orion. This, though not in area the largest, is by far the most brilliant and interesting of all the constellations, both as regards its naked-eye stars and its usefulness to the navigator. It is situated in England, as it comes to the meridian in the winter at a very convenient altitude. Its 2 brightest stars, β (Rigel) and α (Betelgeuse), are both, especially when seen in conjunction with the Sun, very conspicuous. Next to them, then, besides, there are 4 of the second magnitude, ν, λ, κ, ξ. Next to β, 2nd, 3rd, 4th, λ, λ', κ', and ν', with 45 stars of mags. 4. Lepus (The Hare) is a small constellation immediately S. of Orion, with the following conspicuous stars: α, β, γ, δ, and ε. Cassiopeia (The Painter) is a southern constellation with the following as its chief stars: α, β, δ. Monoceros (The Table Mountain), in the Southern Hemisphere, is a large but unimportant of all the accepted constellations, and has no star brighter than γ. Columba Noachii (Noah's Dove), generally called Columba, is a small constellation to the S. of Lepus, and only partly visible in England. It contains only one bright star. Camelopardalis (The Camelopard) is a long, straggling con- stellation with a large number of 4th-magnitude stars, but none brighter than γ. Auriga (The Charioteer) is a constellation occupying a large area, and with one star in particular, α (Capella), which is very bright, being invisible only in the darkest parts of the second brightness class in England, ranking after Sirius. The other bright stars are: β, δ; 2nd, 3rd; γ; 2nd; κ; λ; μ; ν; ω; π'. Canis Major (The Greater Dog). This, though quite a small constellation in area compared with many others of its conspicuous stars, including the brightest of all, Sirius. The other bright stars are: α, β; δ; 1st; β', 2nd; γ; 2nd; λ', μ', ν', and Flamingoes' tail and 28th, both about λ'. Comet (The Twins) has 2 stars with familiar names as 316 CONSTITUTIONS: R.A., 7 H. O.M. 10 H. TO O.M. leaders, together with several others of lesser magnitude. The chief stars are : (β) Piscis, i, (α) Cassiopeia, I, y, z, p, q, r, s, t, u, v, w, x, y, z, Memoceros (The Unicorn) has 2 stars of mag. 4 and nothing larger; it is, however, not an unimportant constellation, being rich in double stars. Cetus (The Leaper Dog), though a small constellation, will always be readily found by its α (Procyon), one of the largest of the first-magnitude stars. The next star, β, is only of mag. 3. Argo (The Ship Argos) is not an easy constellation to describe because of its great extent and, by way of facilitating work in its construction, it has been divided into two parts by the International divisions, respectively called Carina (The Keel), Malus (The Mast), Puppis (The Poop), and Vela (The Sails), to which some add a fifth, Pyxis Nautica, a part of Malus. The conspicuous stars are α and β Carinae; α is a very bright star of mag. 1.5; β is a second magnitude star of mag. 2.8; γ Carinae is a third magnitude star of mag. 3.2; δ Carinae is a fourth magnitude star of mag. 4.2; ε Carinae is a fifth magnitude star of mag. 5.2; ζ Carinae is a sixth magnitude star of mag. 6.2; η Carinae is a seventh magnitude star of mag. 7.2; θ Carinae is an eighth magnitude star of mag. 8.2; ρ Carinae is a ninth magnitude star of mag. 9.2; σ Carinae is a tenth magnitude star of mag. 10.2; τ Carinae is an eleventh magnitude star of mag. 11.2; μ Carinae is a twelfth magnitude star of mag. 12.2; ν Carinae is a thirteenth magnitude star of mag. 13.2; ξ Carinae is a fourteenth magnitude star of mag. 14.2; ο Carinae is a fifteenth magnitude star of mag. 15.2; π Carinae is a sixteenth magnitude star of mag. 16.2; ρ Carinae is a seventeenth magnitude star of mag. 17.2; σ Carinae is an eighteenth magnitude star of mag. 18.2; τ Carinae is an nineteenth magnitude star of mag. 19.2; ρ Carinae is a twentieth magnitude star of mag. 20. Pegasus (The Flying Horse) is one of the most conspicuous stars in the heavens, being but slightly inferior to Sirius, which it completely precedes in rank by about 18 m. Lyra (The Lyre) contains no conspicuous combination to find its brightest star, α, being only β ; and the next one, Flamsteed's γ, only β ; but ζ Cancer (The Crab). The most conspicuous star is β, only γ ; but the cluster "Præcipua" will indicate this constellation to the naked eye. Volans (The proper name of this southern constellation is Pisces Volans (The Flying Fish); but, as there are other Fishes in the heavens—namely, the Southern Cross and Eridanus (Australia)—it has been agreed to drop the third Pisces and use only the word "Volans." Its chief stars are α and β ; both about γ . Andromeda (The Air-pump). The brightest star is α only of mag. 4. A diagram showing the constellations Pegasus and Lyra. Fro. 336 PLATE CXXXIV. The "Southern Cross." 340 Figs. 357 PLATE CXXXV. The Spiral Nebula, 51 M. Canum Venaticorum (Earl of Rosse). 197 **CONSTELLATIONS : R.A., I.O. H. T.M. TO I2. H. 20 M. 317** **Sextans (The Sextant) is an insignificant constellation, and its brightest star #4# is $\alpha$ Sextantis (The Lesser Lion) lies to the N. of Leo Major ; its brightest star is Flamsteed's #5# $\alpha$, of mag. 4. Leo (The Lion). The prominent feature of this constellation is the double star $\beta$ Leo, which is a binary. The chief stars are : $\alpha$ (Regulus), $\gamma$ $\beta$ $\beta$, $\beta_2$, $\gamma_2$, $\epsilon_2$, $\delta_2$, $\eta_2$, all $3^{\circ}$, and $\omega_2$ Chamaeleon. This is a small and unimportant constellation of magnitude 4, with a bright star brighter than $\alpha$. Hydra (The Water-snake). A long, faint constellation extending through more . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 hours of R.A. Chief stars : $a$, $c$, $v$, $w$, all about #3# $3^{\circ}$. (See also "Cetus".) This has already been some- what fully described on a previous page. Its chief stars are : $\alpha$ (Aldebaran), $\gamma$ ($\beta$ Dube), and $\beta$ (Benetean), both $2$: $\xi$ (the "Bull"), $3$: $\zeta$ (the "Horse"), $4$: $\eta$ (the "Horse's Head"), $5$: Crater (The Cup) is a small constellation sometimes treated as part of Hydra. Its 2 principal stars are : Flamsteed's 19, and 20, both $3^{\circ}$. The name is that of a mythological creature. Cetus (The Whale). This is another insignificant constellation, small in size, but with conspicuous stars which suggested its name. Opinions seem much divided as to whether it really is a striking constellation or not. It is often called the "Whale". The fol- lowing is the opinion of Mr. W. G. Clibb, F.R.A.S., #6# : "The Southern Cross" is formed by five stars, of which only one is at its centre, and the other four are arranged in two parallel magnitudes. Closely following, a few degrees away, are the two bright stars $\alpha$ and $\beta$ Centauri, which are sometimes called "The Pointers." When the cross is vertical its longest diagonal points towards the North Star, and when it is horizontal it points approxi- mately found by prolonging this diagonal 48 times its own length in the direction of the South Pole. Altogether these two stars of the Centauri and those of the Southern Cross make a most remarkable group, the most characteristic star-group of the Southern Hemisphere. 318 CONSTITUTIONS: R.A., 12 H. 30 M. TO 15 H. 10 M. Ceresu (The Crow). A small constellation with some very bright stars, several of which are suspected to be variable. The 4 chief stars, α, β, γ, and δ, both 3, and a and b, both 3, form a trapezium. Mercurius Australis (The Southern Flap) is a southern constella- tion. Chief stars: α, β, γ, δ, and B.A.C., γδεβ, both 3. Coma Berenices (Berenice's Tresses) is a small constellation of medium-sized stars distributed at somewhat even intervals. The chief star, α, is only 44, but there are 17 as bright or brighter than 5. Caeus Pemeticus (The Hunting Dog). This constellation has but one star of any importance, called also "Cor Caroli". Hevelius desired to form this into a figure. See Charles I. Cepheus (The Centaur) is a large and northern southern constellation with many bright stars, none of which are visible in England. These are: α', β', both of mag. 1.1; ν', ν", ν', ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν", ν". It is a constellation chiefly noted for its many nebulae. The other chief stars are: α' ε' ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε" ε". Bootes (The Bear Leader). This is one of the largest of the northern constellations, and possesses in a (Arcturus) one of the most brilliant of the northern stars; its rivals being Auriga, and Virgo. Its other chief stars are: α' β' γ' δ' e' f' g' h' i' j' k'. Circinus (The Compasses) is a very small southern con- stellation with two bright stars. Lupus (The Wolf) is a southern constellation, a mere frag- ment of which is visible in England. The bright stars are: α, β, γ, δ; α', β', γ', δ', e', f', g', h', i', j', k', all of mag. 2. Libra (The Scales) is a small constellation in the southern horizon that it is not easy to get hold of it, especially as its visibility coincides with the short nights of the English summer. Its CONSTELLATIONS: R.A., 15 H. 30 M. TO 16 H. 50 M. 319 principal stars are: β, α, γ, and ε Flamsteed's 20, both about 3. Apus (sometimes called Avis Indica, The Bird of Paradise) is a small constellation not far from the South Pole, and its big star is α. Serpens (The Serpent) is a straggling constellation, much mixed up with Ophiuchus. The chief stars are: α, β, γ, δ, ε, ζ, η, θ, ι, κ, λ, μ, ν, ρ, σ, τ, ω. Cepheus Borealis (The Northern Crown) bears more resemblance to its name than most of the constellations do. Chief stars: α, β, γ, δ; with 13 stars between α and β. Taurus (The Bull) is a large constellation situated in the southern hemisphere, with several bright stars: α, β, γ, δ, ε, ζ, η, θ, ι, κ, λ each 3. Little Minor (The Little Bear) is often spoken of as being a facsimile of the Great Bear, but the idea is rather far-fetched. The real importance of this constellation is due to the Northern Polar point and the Pole Star being within its boundaries. Its chief stars are: α and β. γ: Norma (The Rule) is an unimportant southern constellation, whose brightest star (γ) is only of mag. 4. Draconis (The Dragon) is a constellation which may almost be said to extend everywhere for it reaches through nearly 12 hours of solar time. It is circumcipated by the difficulties of study because it is obscured by the fact that when on the meridian it is absolutely in the zenith. Chief stars: γ²; β²; γ³; α²; β³; γ⁴; α³; β⁴; γ⁵; α⁴; β⁵; γ⁶; α⁶; β⁷; γ⁷; α⁷; β⁸; γ⁸; α⁸; β⁹; γ⁹; α¹; β¹; γ¹; α¹²; β¹³; γ¹⁴; α¹⁵; β¹⁶; γ¹⁷; α¹⁸; β¹⁹; γ¹¹. Aries (The Ram) is a small constellation which has been unfavourably placed for observers in England. Its principal star, α of mag. 1, is known as Antares ("the rival of Mars"), a name given to mark its red colour. The other chief stars are: α²: δ²; z²; ε²; z³: β³: ε³: α³: ε³: z³: π³: ξ³: η³: all mag. 3. Ars (The Altar) is a small constellation, but with a good 320 CONSTITUTIONS: R.A., 17 H. M. O. TO 19 H. M. O. share of medium-sized stars. These are: β, z1; α, z5; λ, z1; ν, z3; j, z6; α, z1; ε, z4; both about 4° apart. (Orion) The Hunter (The Hunter) is Serpens Caput (The Serpent-bearer), is much mixed up with Serpens, the animal carried, and with Hercules. The chief stars are: α, z2; ν, z2; δ, z2; ζ, z2; α, z3; ε, z6; all about 3° apart; ν, z1 and Flamsteed's ν7, both about 4° apart. (Leo) Leo Minor (The Lion Minor) is a small constellation with a great variety both of naked-eye and of telescopic objects. Its principal stars are: β, z2; λ, z4; δ, z2; π, z3; γ, z3; with 47 other stars of magnitude 5 or less. Corona Australis (The Southern Crown) is a southern constellation with no stars brighter than mag. 4. It is to be noticed that 6 of its naked-eye stars are disposed in a curved line. Scutum Soskini is sometimes called Clypeus Soskini, but the single word Scutum (The Shield) is its more usual designation. Telescopium (The Telescope) is a small southern constellation, the brightest star of which is α3. Lyra (The Lyre) is a very small constellation in small size, but it possesses in its α (Vega) a very brilliant star-magnitude star, and a great variety of important telescopic objects. After Vega comes α1 and α2 (Altair). Sagittarius (the Archer), by reason of its low altitude in England, is not generally appreciated, but it contains a considerable number of important stars. Thus: σ, ε, ν2; β, ν2; δ, ν3; α5, ν5; all at least 3° apart; γ1 and γ2; π1 and π2 with 56 stars from 4° to 5°. Pavo (The Peacock) is a small southern constellation with no stars brighter than mag. 4. Aquila (The Eagle), though only a small constellation, is rich in bright and double stars. The chief stars are: α1; y, z2; μ1; λ1; ε1; ν1; λ2; all about 3° apart while α is a bright 4°. Cepheus (The Archer) is a small but ancient constellation, with 2 stars, y, s, both of them about 3°. CONSTELLATIONS, R.A., 20 H. 10 M. TO 22 H. 20 M. 321 Volpulica et Anser. As a fox and a goose were two things which formerly were supposed to go together (for a short time), so the constellation of the Fox and the Goose is now. The Fox and the Goose has long since disappeared down the Fox's throat, and astronomers only talk now of the Fox. The brightest star is α, 44°, 56' 17" (Aldebaran). The second brightest star is β, 44°, 58' 17" (Afer). Cygnus (The Swan) is a large and important constellation, with much in it to interest all classes of students. A rich part of the Milky Way occupies a considerable area of it, and a number of interesting stars are found in its prominent features. The chief star is α (Deneb) 1°, 2°; β (Alpha Cygni) 1°, 2°; γ (Gamma Cygni) 1°, 2°; δ (Delta Cygni) 1°, 2°; ε (Epsilon Cygni) 1°, 2°; ζ (Zeta Cygni) 1°, 2°; η (Eta Cygni) 1°, 2°; θ (Theta Cygni) 1°, 2°; ι (Iota Cygni) 1°, 2°; κ (Kappa Cygni) 1°, 2°; λ (Lambda Cygni) 1°, 2°; μ (Mu Cygni) 1°, 2°; ν (Nu Cygni) 1°, 2°; ω (Omega Cygni) 1°, 2°. Delphineus (The Dolphin) is an unimportant northern constellation, the brightest star of which is β, 3°. Cepheus (The King) is a constellation low down in Eng- lish sky with not much at all for the naked eye. Its chief stars are α, β, δ, γ, ε', α", c", d", e". Microscopium (The Microscope) is a small southern constella- tion whose brightest star is α. Equuleus (The Little Horse) is a small constellation whose brightest star is α. Piscis Australis (The Southern Fish) is a small southern constellation whose brightest stars are α and β. γ and δ are of e. mag. Sf is distin- guished for its remarkably large proper motion. Pisces Australis (The Southern Fish) has only one bright star, β. Cepheus is a large and straggling constellation which reaches nearly to the North Pole. Its chief stars are α (Aldebaran) and β. Crux (The Crane) is a southern constellation which though, small, contains a considerable number of important stars. There are α, β, γ, δ', ε', ζ', η', θ', ι', κ', λ', μ', ν', ω'. Aquarius (The Water-Bearer) has for its two principal stars α and β, both about δ, ε', α", c", d", e". 322 CONSTITUTIONS, EA, 22 H. 25 M. TO O. H. O. M. Lacerta (The Lizard) is a small northern constellation, of which the largest star, $\alpha$, is only 4 ; but there are 15 other stars up to 3. Pegasus (The Winged Horse). The so-called " Square of Pegasus " (of which is Andromeda, sometimes called δ Pegasi, is one member) is familiar to most star-gazers. The chief stars of Pegasus are $\beta$ Pegasi (the Star of the Wing), $\gamma$ Pegasi (Algenb), $\beta$ 3 ; λ 3 ; and $μ$, δ, 3. There are 30 stars 4 to 5. Toucan (The American Goose). This southern constellation includes the bright star, $\alpha$ Tuc. Ophiuchus (The Ophidian) is the constellation which includes the South Pole. The brightest star is $μ$, 34 ; but the nearest star to the Pole is $\sigma$, 34 . A diagram showing the constellations Lacerta, Pegasus, and Ophiuchus. APPENDIX I. STATISTICS RESPECTING THE PLANETS AND THEIR SATELLITES.
SOME STATISTICS OF THE PLANETS.
Name Mean Mean Mean Mean Mean Mean Mean Mean d. h. m.
Moon A 0°78 13°56'00" (13°56'00") 13°56'00" (13°56'00") 13°56'00" (13°56'00") 13°56'00" (13°56'00") 13°56'00" (13°56'00") 13°56'00" (13°56'00") 24 ± 5
Venus A 0°78 13°56'00" (13°56'00") 13°56'00" (13°56'00") 13°56'00" (13°56'00") 13°56'00" (13°56'00") 13°56'00" (13°56'00") 13°56'00" (13°56'00") 24 ± 5
Terra A 2°78 24°78'< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td>< td:< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t< t:< s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s: s:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e:< e::< br/>






































































Sun's Mean Distance from Sun: Diameter of Sun: Diameter of Earth: Diameter of Moon: d. h. m.
929 km (929 km) 879 km (879 km) 879 km (879 km) 879 km (879 km) 24 ± 5
Moon's Mean Distance from Sun: Diameter of Moon: Diameter of Earth: Diameter of Moon: d. h. m.
929 km (929 km) 879 km (879 km) 879 km (879 km) 879 km (879 km) 24 ± 5
Venus's Mean Distance from Sun: Diameter of Venus: Diameter of Earth: Diameter of Venus: d. h. m.
929 km (929 km) 879 km (879 km) 879 km (879 km) 879 km (879 km) 24 ± 5
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Name or Number Inclination Eccen- tricity Mean Daily Sidelock Mass
The Moon 8 5 47 V0549 13 10 25 d. h. m. 27 7 43 0012552
The SatelliteS of THE EARTH
The Moon 8 5 47 V0549 13 10 25 d. h. m. 27 7 43 0012552
The SatelliteS of THE EARTH
Phobos 27 28 O0217 128.8 0 7 59 /
Demos 27 28 O0217 128.8 0 7 59 /
The SatelliteS of JUPITER.
V 2 20 O0050 22.6 d. h. m. /
I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II II III III III III III III III III III III III III III III III III III III III III III III III III III III III III III III III III III III III III III IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV IV V VI VII VIII IX X XI XII XIII XIV XV XVI XVII XVIII XIX XX XXI XXII XXIII XXIV XXV XXVI XXVII XXVIII XXIX XXX XXXI XXXII XXXIII XXXIV XXXV XXXVI XXXVII XXXVIII XXXIX XL XLXI XLX L LX LXI LXII LXIII LXIV LXV LXVI LXVII LXVIII LXIX LXX LXXX LXXXI LXXXII LXXXIII LXXXIV LXXXV LXXXVI LXXXVII LXXXVIII LXXXIX XC XCX CXC CX CXCX CXCXI CXCXII CXCXIII CXCXIV CXCXV CXCXVI CXCXVII CXCXVIII CXCIX DC DCC DCCC DCCCX DCCCXI DCCCXII DCCCXIII DCCCXIV DCCCXV DCCCXVI DCCCXVII DCCCXVIII DCCCIX DCX DCXX DCXXX DCXXXX DCXXXXI DCXXXXII DCXXXXIII DCXXXXIV DCXXXXV DCXXXXVI DCXXXXVII DCXXXXVIII DCXXXXIX DCXI DCXII DCXIII DCXIV DCXV DCXVI DCXVII DCXVIII DCIX DCXX DCXXX DCXXXX DCXXXXI DCXXXXII DCXXXXIII DCXXXXIV DCXXXXV DCXXXXVI DCXXXXVII DCXXXXVIII DCXXXXIX DCXI DCXII DCXIII DCXIV DCXV DCXVI DCXVII DCXVIII DCIX DCXX DCXXX DCXXXX DCXXXXI DCXXXXII DCXXXXIII DCXXXXIV DCXXXXV DCXXXXVI DCXXXXVII DCXXXXVIII DCXXXXIX DCXI DCXII DCXIII DCXIV DCXV DCXVI DCXVII DCXVIII DCIX                                                                  The SatelliteS of SATURN.
Mimas, Enceladus, Tethys, Dionne, Titan, Hyperion, Epimetheus, Phoebe, Ariel, Umbriel, Oberon, Titania, Umbriel, Ariel, Umbriel, Oberon, Titania, Umbriel, Ariel, Umbriel, Oberon, Titania, Umbriel, Ariel, Umbriel, Oberon, Titania, Umbriel, Ariel, Umbriel, Oberon, Titania,
Mimas27 29O00190.00000000000000000000000000000000000000000000000000000000000000111111111111111111111111111111111111111111111111111111111111111111111111333333333333333333333333333333333333333333333333333333333333333444444444444444444444444444444444444444444444444444444445555555555555555555555555666666666666666666666666666666677777777777777777777777778888888888888888888888888888889999999999999999999999999999999999999999999999999999999999999999999999999999999  22.2d. h. m.////////////////////////////////////
Mimas
Enceladus
Tethys
Dione
Titan
Hyperion
Epimetheus
Phoebe
Ariel
Umbriel
Oberon
Titania
Ariel
Umbriel
Oberon
Titania
Ariel
Umbriel
Oberon
Titania
Ariel
Umbriel
Oberon
Titania
Ariel
Umbriel
Oberon
Titania
Ariel
Umbriel
Oberon
Titania
Ariel
Umbriel
Oberon
Titania
Ariel
Umbriel
Oberon
Titania,
<span style="color:red;">(From the Connaissance des Temps, 1st)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)
(From the Connaissance des Temps, 2nd)

SOME STATISTICS OF THE PLANETS.

Name or Number:

Inclination Eccen- tricity:

Sidelock Mean Daily:

Mass:

The Moon:

SatelliteS of THE EARTH:

SatelliteS of JUPITER:

SatelliteS of SATURN:

SatelliteS of URANUS:

SatelliteS of NEPTUNE:

SatelliteS of PLUTO:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

SatelliteS of Eris:

SatelliteS of Makemake:

SatelliteS of Haumea:

SatelliteS of Orcus:

SatelliteS of Quaoar:

Description: A table listing various celestial bodies and their characteristics. APPENDIX II. CATALOGUE OF CELESTIAL OBJECTS EASY FOR SMALL TELESCOPES. The following Catalogue includes, with objects already men- tioned, others which may be seen without difficulty in small telescopes; though, to bring out their specially attractive features, large telescopes may often be necessary.
MERCURY. PLANETS. CERES.
VENUS. JUPITER. SATURN.
MARS, PLUTO. NEBULAE.
DOUBLE STARS, CLUSTERS, AND NEBULAE.¹ No. Name. R.A. Decl. Description. 1 47 Tucanae. h. 30 m. 56 s. + 4° 38' Superb globular cluster. 2 31 M Andro. h. 30 m. 56 s. + 4° 38' The Great Nebula. 3 2 Cassiopeia. o 37 m. 56 s. + 4° 38' Double star, mags. 4+. o 47 m. 56 s. + 4° 38' Double star, mags. 4+. ¹ Extracted from The Cycle of Celestial Objects by Smyth and Chambers, and edited by J. H. Latham, and published at every telescope. 39
APPENDIX.
No. Name. R.A. Decl. Description.
4 Nubecula Minor b, m, n -73 55 Mass of clouds.
5 Arietis . . . 148 2 -57 18 Clouds, figs. 41;
6 y Andromedæ 17 54 +41 51 Double star, figs. 35;
7 33 VI Persei. 2 12 +56 41 Doubie cluster in fine
8 e Ceti 2 14 -32 5 Celebrated variable,
9 a Ceti 2 57 +33 0 variable, with red,
10 b Persei . . . 3 39 +40 34 invisible at night.
11 Tauri . . . 31 43 +23 47 Famous star, figs. 41;
12 e Orionis 26 53 -02 22 Famous star, figs. 25;
13 m Tauri . . . 28 27 +23 57 Famous star, figs. 41;
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . .
e Arcturus . . ..
e Arcturus . ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus ..
e Arcturus..		The Great Nebula in the star <sup>6</sup>, figs. <sup>6</sup>, <sup>7</sup>, <sup>8</sup>, <sup>9</sup>, <sup>10</sup>, <sup>11</sup>, <sup>12</sup>, <sup>13</sup>, <sup>14</sup>, <sup>15</sup>, <sup>16</sup>, <sup>17</sup>, <sup>18</sup>, <sup>19</sup>, <sup>20</sup>, <sup>21</sup>, <sup>22</sup>, <sup>23</sup>, <sup>24</sup>, <sup>25</sup>, <sup>26</sup>, <sup>27</sup>, <sup>28</sup>, <sup>29</sup>, <sup>30</sup>, <sup>31</sup>, <sup>32</sup>, <sup>33</sup>, <sup>34</sup>, <sup>35</sup>, <sup>36</sup>, <sup>37</sup>, <sup>38</sup>, <sup>39</sup>, <sup>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...&g...
No.Name.R.A.Decl.Description.
APPENDIX.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Name.R.A.Decl.Description.
APPENDIX.
4
5
6
7
8
9
10
11
12
13
Nubecula Minor.Arietis. y Andromedæ. VI Persei. Ceti. Ceti. Persei. Tauri. Orionis. Tauri. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis. Orionis.m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n, b, m, n,-73 55,-57 18,+41 51,-32 5,+40 34,+23 47,-02 22,+23 57,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -00,+00 -...Mass of clouds.Fine cluster of stars.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Famous star.Arietis y Andromedæ VI Persei Ceti Ceti Persei Tauri Orionis Tauri Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orionis Orin...
APPENDIX.
4
5
6
7
Nubecula Minor.Arietis y Andromedæ VI Persei Ceti Ceti Persei Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri Tauri.m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b...-73 55,-57 18,+41 51,-32 5,+40 34,+23 47,-...Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Mass of clouds.Arietis y Andromedæ VI Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Ceti Persei Ceti Cei...
APPENDIX.
4
Nubecula Minor.Arietis y Andromedæ VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Persei VI Perpei Vi...m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,n,b,m,...b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b.m.n.b...-73 55,-57 18,+41 51,-32 5,+40 34,+...Mass of clouds.Arietis y AndromedæVIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivIPerseivI...
APPENDIX.
4
Nubecula Minor.Arietis y AndromedæVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIVIV...m,n,b,m,...b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b....b........-73 ...+4 ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+ ...+

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APPENDIA: APPENDIX. 327 ; ;
No. Name. R.A. Dectl. Description.
25 54 Leonis m. a.
10 50 28		 25 17 Double star, mags. 4j and 7; d.e. 63°
26 a Crucis 12 21 0 -68 33 Quintuple star, mags. 1j, 2j, 3j, 4j and 5j;
27 c Crucis 12 25 6 -58 33 Star, mag. 2, Companion, mags. 4j and 5j;
28 y Virginis 12 36 6 -54 Binary star, both mag.
4: dit. 67;
29 c Crucis 12 47 42 -59 45 Bright globular cluster.
30 a Canum Venet. 12 51 00 -55 41 Doubler star, mags. 2j and 3j;
31 f Urse Majors I 12 51 00 -55 47 Doubler star, mag. 3;
32 e Centauri 13 09 45 -66 26 Magnificent double, mag.1 and mag.2;
33 e Centauri 14 32 47 -66 26 Magnificent double, mag.1 and mag.2;
34 b Bootis 14 36 20 -66 00 Doubler star, mags. 3;
d.e. dit.;
dit. dit.
dit.
dit.
dit.
dit.
dit.
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dit.;A star diagram showing two stars in a double star system with magnitudes indicated by different colors (green for the primary star and red for the secondary star).
Bright globular cluster.
Double star, mags. 3j and
mags.4j;
d.e. dit.;
d.d. dit.;
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Double star, mags.4j and
mags.5j;; d.e.63°;

Doubler star, mags.2j and
mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.68°;

Doubler star, mags.3j;; d.e.

No.
INDEX. A Achromatism of telescopes, 35 Adams, J. C., 102; remarks as to Neptune, 103; sector comets, 188 Astrometry, 176 Age of the Moon, 27 Albion, 172 Algol, 8 Petrol, 222 Alhazen (Alhazen), 38 Altazimuth mounting, 260 Andromeda (constellation), 310, 335 metres of, 174; Great Nebula in, 41 Annular eclipses of the Sun, 115 Aperture, 176 Apophysis, 59 Apparent movements of the planets, Appendix I. Directions respecting the Appendix II. The orbits of the planets. Logic of Celestial Objects, 321 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Metaphysics of the Heavens, 321-327 metres in, 174 Bally's Bands, 145 Bernardi's Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law), Law (Bernardi's Law),Law (Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'),Law(Bernardi'). Bernardo', L., his observatory, Biddle's Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet', Biddle Comet'. Bernoulli' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory, Bessel' L., his observatory， xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx xxx **INDEX.** A Chromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Achromatism of telescopes. Astronomy: Different branches of astronomy: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomical observations: Astronomicall Observations: Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two different sciences. Astrology and astronomy are two不同科学。 Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy Astronomy 330 INDEX. Broun's Periodical Comets, 139, 160 Buchanan, R. W., ed. Calvino, Rafael, of 185 Caloricai rays of the Sun, 85 Cantor, (contestation), 311, 315 Cantor, (contestation), 311, 315 Cantor, (contestation), 311, 315 Cantor, (contestation), 311, 315 Cantor, (contestation), 311, 315 Cantori, J. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Cassini, D. J., Bk. Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestation), 317 Calvinus (contestion) INDEX. 334
H Gladiator, 50
Earth, 13 Gladiator's chamber, 230
Earth-killer, 36 Glasmakern on the Sun's surface, 7
Eccentricity of orbit, 60 Grecian, 189
Eclipse of the Sun, 127 Grecian Observatory, 205
Eclipse expeditions, 129 Grecian telescope, 157
Eclipse of the Moon, of, 1331 Grecian telescope, 157
futures, 127 Grecian telescope, 157
Fulgence of Jupiter's satellites, 143 Grecian telescope, 157
Eclipses of the Sun, 124, 125: ob- Grecian telescope, 157
Observations of, 126 Grecian telescope, 157
Eclipses of the Moon, 116 Grecian telescope, 157
Earth's shadow on the Moon, Grecian telescope, 157
Ellipsis, Propertie of, o6: how to draw ellipses by hand, o8 Grecian telescope, 157
Ephelid nebulae, 227, x23 Hale, G. E., o9
Ephelid Nebulae, o8: how to draw ellipses by hand, o8 Hale's Observatory, o90
Elipsoide nebulae, x27, x23 Harvard Observatory, o96
Elongation of Mercury, o8: Hale's Observatory, o90
Elipsoide nebulae, x27, x23 Hale's Observatory, o90
Elipsoide nebulae, x27, x23 Hale's Observatory, o90
Elipsoide nebulae, x27, x23 Hale's Observatory, o90
Elipsoide nebulae, x27, x23 Hale's Observatory, o90
Elipsoide nebulae, x27, x23 Hale's Observatory, o90
Elipsoide nebulae, x27, x23 Hale's Observatory, o90
Elipsoide nebulae, x27, x23 Hale's Observatory, o90

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(continued)                                                                           <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img> <img>Observatory building</img>&nb 332 INDEX.
H.Hale's Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,o96: Harvard Observatory,
o90: Harvard Observatory,
Latte-Mercureal plants, 66
Iron, Meteoric, 189
Isle of Wight, Tides around, 51		 Minutude of stars, 196, 200; list of
stars of the first magnitude, 249
Magnitude of the star system, populat
ion of, 249; number of stars, 250
Maga, Astronomical, 445
Nasa, 478; Nasa's space station, 478
on, 81; meteors of, 103; see also Nasa
Johnson, R.C., J. 27
Johnson, W.R., K., 50
Jupitier, 84		 Mann distance of a Planet, 353
Mean distance of a Planet, 353
Mercurial meteorites, 190
The Warner Prize, 146
Meteors and meteorites, 190
Mercury, 68; phases of, 57; transits
of, 57; transit of the Moon by, 57
Messier, his catalogue of nebulae, 219
Meteors: stonies, 190
Meteors: stony meteorites, 190
Milky Way, 749
K Mills Cirl, 232; 236
Moonlighting: his researches on twinkl-
ing stars, 236
Keller's Laws, 59
Kibler, H.J., his duties, 146
Kullman's Survey diagrams, 447		 Moonlighting: his researches on twinkl-
ing stars, 236
L Moons: their motions about the Sun and Earth, 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), 278; their motions about the Sun and Earth (continued), INDEX. 353
Nebulose stars, 207
Nicolella, Magnesia, variation in the inclination of, 16
Synodical, 18
New stars, 218
Newcomer stars, 205, 302
Newcomer telescopes, 237
November stars, 189-190, increasing, 85
November meteorites (Lecointe), 186, 197
Nebulosity, 207
Nebulosity, Minor, 741
Nocturna of a Sun of opus, 12; of a comet, 11
O
Glittering stars, 208
Observations of eclipses, 299
Observatory, 384; construction of, 385
Oculatissima, IIx., 104
Oculatissima, IIIx., in Chryseis Sobolevskii, 104
Ocypus, 259
Ophionites, 329; new star IIx., 320
Ophionites, IIIx., new star IIx., 320
Ophionites, IVx., new star IIx., 320
Ophionites, Vx., new star IIx., 320
Ophionites, VIx., new star IIx., 320
Ophionites, VIIx., new star IIx., 320
Ophionites, VIIIx., new star IIx., 320
Ophionites, IXx., new star IIx., 320
Ophionites, Xx., new star IIx., 320
Ophionites, XIx., new star IIx., 320
Ophionites, XIIx., new star IIx., 320
Ophionites, XIIIx., new star IIx., 320
Ophionites, XIVx., new star IIx., 320
Ophionites, XVx., new star IIx., 320
Ophionites, XVIx., new star IIx., 320
Ophionites, XVIIx., new star IIx., 320
Ophionites, XVIIIx., new star IIx., 320
Ophionites, XIXx., new star IIx., 320
Ophionites, XXXIIx., new star IIx., 320
Ophionites, XXIx., new star IIx., 320
Ophionites, XXXIv., new star IIx., 320
Ophionites, XXXIx., new star IIx., 320
Ophionites, XXXVIIv., new star IIx., 320
Ophionites, XXXVIIIv., new star IIx., 320
Ophionites, XXXIXv., new star IIx., 320
Ophionites, XLVIIv., new star IIx., 320
Ophionites, XLVIIIv., new star IIx., 320
Ophionites, XLIXv., new star IIx., 320
Ophionites, LIVv.
Orbital diameters of comets (see Comets), p. 154; of planets (see Planets), p. 154; of asteroids (see Asteroids), p. 144; shooting stars (see Shooting stars), p. 17
Periods of the planets, p. xiii; of comets, p. xiii; of meteors (see Meteors), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novae (see Novae), p. xiii; of novne A diagram showing the orbits and positions relative to each other for several celestial bodies.
Quadrature - Marsilea (constellation) meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , meteors , me A diagram showing the orbits and positions relative to each other for several celestial bodies. 334 INDEX. II. Raduiti points of meteors, 174 Bastille-voyeur of a planet, 150 Rainfall and snow-storms, 17 Rumour of a comet, 186 " Red Flames" in eclipses of the Sun, 88 Red spot on Jupiter, 85 Red spots on Saturn, 100 Refraction telescope, 256 Refracting telescope, 256 Right ascension, 213 Right ascension of the Sun, 213 Roberts, J., 233 Rosse's telescope, on a log, 90 Rouand's Comet, 168 Rose, Third Earl of, 233 Rossi's Comet, 107 Sir of the planets, 233 Sagittarius (constellation), 321; 301; Sahara in, 238 Saturn (planet), 89; in Jupiter, 87; Saturn's rings, of Uranus, 100; Saturn's rings in Jupiter, 87; Saturn's rings in Neptune, 100; Saturn's rings in Uranus, 100; Saturn's rings in Venus, 100; Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Saturn's rings in the Solar System, Sun (star), 29 Secchi, A., 203; bin Star types, 204; semi-major-axis of a planet' s orbit, 64 Shadow bands in eclipses of Sun, 174 Shadow cast by Venus, 74; of Moon at full moon, 74; of Mercury at transit, 135 Shortest-asterism, 173 Shortest-asterism of Mars, 173 Silvered-glass reflectors, 357 Silvered-glass reflectors of Mars, 256 Smith, Admiral W. B., 395 Smithsonian Institution, Washington D.C., U.S.A., 427 Spectroscopic Telescope, Tant. - Astronomical - Alkali - Spectrum analysis, 301 Spectroscopic Telescope for Transit Spectra, 379 Spuriously periodic meteors, 256 Spuriously periodic meteors on Jupiter, 84; on Saturn, 69 Spuriously periodic meteors on Uranus, 205 Spuriously periodic meteors on Venus, 205 Stable stars (of Sun), 256; doublet-, 205; binary-, 206; multiple-, 205; single-star-, 205; triple-star-, 205 Star-finder: Kullman', s' map - doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet-, doublet- Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Index - Star-colour index of Sun (photometer), Tant. - Astronomical - Coloured - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. - Star-colour index of Sun (photometer), Tant. Tables for Eclipses and Satellite(s) Tandem telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 Telescope for Transit Spectra, 379 INDEX. 335
TELESCOPES, 336 V
Teléscopes, various kinds of, 258 Variable nebulae, 170
plans as to the purchase of, 259 Variable stars, 211
various sizes of, 259 Vigour of light, 290; of the tidal wave,
use of, 260 Wave-lengths, 290
Teléscope, 147 Venus, 731; transit of, of, 143; sun-
Teléscopic motors, 173 position of, with respect to the sun, 142;
Transit of Venus, 173 phases of, 142; transit of, of, 143;
Tempest's Periodic Comet, c. x8 Voyage to the Planeti, 107
Terminator of the Moon, 30 Voyages to the Moon, c. x8; x9; x91;
Termination of the Sun's Rotation, see Rotation of the Sun; see also Sun's Rotation; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun; see also Rotation of the Sun;
Terminator (definition) of, 44 Dumb-bell Nebula, p. i49
Time and its Measurement, p. i49 Dumb-bell Nebula (see), p. i49
Timothy's Comet, p. i50 Dumb-bell Nebula (see), p. i49
Tinumius, g3 Dumb-bell Nebula (see), p. i49
Tinumius' Comet, p. i50 Dumb-bell Nebula (see), p. i49
Tinumius' Comet (see), p. i50 Dumb-bell Nebula (see), p. i49
Tinumius' Comet (see), p. i50 Dumb-bell Nebula (see), p. i49
Tinumius' Comet (see), p. i50 Dumb-bell Nebula (see), p. i49
Tinumius' Comet (see), p. i50 Dumb-bell Nebula (see), p. i49
Tinumius' Comet (see), p. i50 Dumb-bell Nebula (see), p. i49
Tinumius' Comet (see), p. i50 Dumb-bell Nebula (see), p. i49
Tinumius' Comet (see), p. i50 Dumb-bell Nebula (see), p. i49
Tinumius' Comet (see), p. i50 Dumb-bell Nebula (see), p. i49
Tinumius' Comet (see), p. i50 Dumb-bell Nebula (see), p. i49
WINDS AND WEATHER.
Weather influences imposed to the Moon, &c., &c., &c., &c., &c., &c., &c., Moon, &c., &c., &c., &c., &c., &c., &c., Moon, &c., &c., &c., &c., &c., &c., &c., Moon, &c., &c., &c., &c., &c., &c., &c., Moon, &c., &c., &c., &c., &c., &c., &c., Moon, &c., &c., &c., &c., &c., &c., &c., Moon, &c., &c., &c., &c., &c., &c., &c., Moon, &c., &c., &c., &c., &c., &c., &c., Moon, &c., &c., &c., &c., &c., &c., &c., Moon, &c., &c., &c., &c., &c., &c., Moon, &c., Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Moon, Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Month Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year. Year.
VARIABLE STARS.
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
Variable stars in our Solar System,
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