Graves, John Thomas (1806–70), jurist and mathematician, was born 4 December 1806 at 12 Fitzwilliam Square, Dublin, eldest son of four boys and one girl of John Crosbie Graves, chief police magistrate of Dublin, and his wife Helena, daughter of the Rev. Charles Perceval, rector of Bruhenny, Co. Cork. Charles Graves (qv), mathematician and bishop of Limerick, was his youngest brother and the poet Helena Clarissa von Ranke (qv) was his sister. Some of his early education was spent at school in Westbury-on-Trym, Somerset. He entered TCD, in 1823 to study mathematics and classics and was awarded the classical gold medal at his degree examination (BA 1827). William Rowan Hamilton (qv) was a fellow student and became a lifelong friend. After graduating he went to Oriel College, Oxford, where he took an MA (1831). That same year he was called to the English bar by the Inner Temple and for a short time went on the western circuit, having previously entered the King's Inns, Dublin. In 1839 he was appointed professor of jurisprudence in University College, London, and was elected examiner in laws at the University of London soon after. He published twelve lectures on the law of nations, contributed to the Law Times (1845) and wrote two articles on Roman law and canon law for the Encyclopædia Metropolitana. Smith's Dictionary of Greek and Roman biography contains his contributions on four Roman jurists. In 1846 he was appointed an assistant poor law commissioner, then – through the influence of his fellow mathematician Sir John Shaw Lefevre – poor law inspector the following year (1847), a position he held until his retirement in 1870.
He was highly regarded as a mathematician in his time. His first paper, ‘An attempt to rectify the inaccuracy of some logarithmic formulae’, was published while he was in his early twenties (Royal Society, Philosophical Transactions, 1829). He considered that his results clarified the subject of logarithms of negative and imaginary quantities, a topic that had caused some controversy. His paper received a mixed response and much discussion. In a later paper defending his position he was supported by his friend W. R. Hamilton, who indicated that Graves's development had helped lead to his own theory of conjugate functions or algebraic couples. Both papers were published in the report of the British Association (1834). Graves published several more papers in the Royal Society's Transactions, the Philosophical Magazine, and the Transactions of the RIA, some of which are listed in the University College Gazette (1887). Throughout his life he continued an active correspondence with Hamilton, in which they discussed and developed mathematical ideas. His initial work on logarithms is said to have played an important role in the development of Hamilton's mathematical conception of quaternions. In his preface to the ‘Lectures on quaternions’, Hamilton expressed his indebtedness to his friend and to their fruitful correspondence.
In addition to mathematics and law, Graves retained his interest in classics and astronomy. He was a member of the Philological Society, the Royal Society of Literature, and the Royal Society (1839), serving on its council. He spent much of his life collecting a magnificent library of early scientific works, which was regarded as one of the most complete and valuable private libraries of its kind. The extensive collection of 14,000 books, manuscripts, and pamphlets was largely devoted to early mathematics (the Euclid collection being the most important), but also included works on the history of physics, applied mathematics, chemistry, and the biological sciences.
Graves was a sensitive and shy man; according to Lefevre, he carried out his dreary job faithfully, although it was far below his intellectual abilities and knowledge. He married (1846) a daughter of William Tooke, FRS, but they had no children. Within a month of his retirement he died 29 March 1870 at home in Cheltenham. He bequeathed to University College, London, his unique library, which is the college's most outstanding and valuable collection. It contains one of UCL's rarest volumes, a previously unrecorded copy of Lunarium ab anno 1490 ad annum 1550, a book of lunar tables printed in Venice c.1490.