Hamilton, Hugh (1729–1805), Church of Ireland bishop and scientist, was born 26 March 1729 at Knock, Co. Dublin, eldest of four sons of Alexander Hamilton, attorney and later MP for Killyleagh (1739–60), and his wife Isabella, a Maxwell of Finnebrogue, Co. Down; there were also two sisters, one of whom married Henry Caldwell (qv). Hugh was educated by Mr Garnett, probably in Belfast, entered TCD (17 November 1742), and graduated BA (1747) and MA (1750). He was elected to fellowship (1751) and was awarded the degrees of BD (1759) and DD (1762). His book De sectionibus conicis tractatus geometricus (1758) was well regarded by contemporary mathematicians; in 1759 he became Erasmus Smith professor of natural philosophy in TCD. Other learned works appeared, including Philosophical essays on vapours (1767) and an essay to prove the existence of God (1784); also papers in the Philosophical Transactions of the Royal Society and the Transactions of the Royal Irish Academy on the barometer and on food preservation using alkali salts; he was one of the founder members of the RIA and was FRS from 1761.
In 1764 he resigned his fellowship to take up the college living of Kilmacrenan, Co. Donegal, but was able to remain a professor till 1769. He was vicar (1767–8) of St Ann's, Dublin, then went to Armagh as dean and built a deanery there; he actively supported schemes for the improvement of Armagh city, including the establishment of a piped water supply and of a county hospital. He was appointed bishop of Clonfert 21 January 1796, and moved to the see of Ossory in January 1799; he never canvassed for preferment, which was unusual at that time. After the act of union in 1800, he received compensation of £15,000 when the borough of Irishtown was abolished. He married (6 August 1772) Isabella Wood of Rossmead, Westmeath, daughter of Hans Wood; her mother was a twin sister of Edward King, 1st earl of Kingston (1726–97). They had five sons, including the Hebraist and clergyman George Hamilton (d. 1830), and two daughters. Descendants include C. S. Lewis (qv), John Millington Synge (qv), and John Lighton Synge (qv); George Alexander Hamilton (qv) (d. 1871) was a relative. Hamilton died of fever in Kilkenny on 1 December 1805, and was buried in St Canice's cathedral there. A portrait and memoir appears in the first volume of his collected works, edited in two volumes by his eldest son (1809). A posthumous oil portrait (c. 1810) by William Cuming (qv), after an original by Gilbert Stuart (qv), hangs in TCD physics department.