John O’Hart (1824 -1902) is probably the single best-known writer on Irish genealogy. His most widely-available work is Irish Pedigrees (or the Origin and Stem of the Irish Nation), first published in 1878, with at least eight subsequent expanded editions.
O’Hart had an extraordinary appetite for work and appears to have read and absorbed every single Irish pedigree published before the 1870s. He was also a passionate nationalist, and this passion shaped and distorted what he wrote. The primary aim of Irish Pedigrees, as its subtitle shows, was to demonstrate the homogeneity and racial purity of the Irish. To this end, O’Hart takes the legendary Milesian origins of the Gaels, extends them back to Adam, via Magog, Japhet and Moses, grafts onto this root every published medieval Irish genealogy, including all of the descents listed in the Annals of the Four Masters, and then extends them all into the 17th, 18th and 19th centuries.
The result is extraordinary. Every Gaelic Irish family is shown to descend from a single forebear, but only by constant jumbling of sources, unacknowledged guesswork and judicious omissions. And as a piece of wonderful inverted Gaelic snobbery, he even demonstrates the Milesian descent of the British royal family.
If this was all the book consisted of, it would merely be a historical curiosity, about as interesting as phrenology. The real tragedy is that it includes much information based on sources that no longer exist.
As the scope of the work expanded through its various editions, O’Hart began to incorporate material relating to the non-Gaels, taken from the original sources in the Public Record Office that were destroyed in 1922. But since he gives no details of the sources, it is almost impossible to sort fantasy from fact. If ever there was an object lesson in the importance of academic citation, Irish Pedigrees is it.
Approach with caution.