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HADLEY, JOHN, M.D. (1731–1764), professor of chemistry at Cambridge, eldest son of Henry Hadley (brother of John Hadley, mathematician [q. v.]) and Ann Hoffman (?), was born in London in 1731, and entered Queens' College, Cambridge, in May 1749. He was fifth wrangler, was elected fellow of Queens' in January 1753, and proceeded B.A. in the same year, M.A. in July 1756, and M.D. in 1763. He became professor of chemistry in 1756, and published the 'Plan of a Course of Chemical Lectures,' 1758. He also wrote 'An Introduction to Chemistry, being the Substance of a Course of Lectures read two years successively at the Laboratory in Cambridge,' 1759; the manuscript is in possession of Professor Cumming of Cambridge. In 1758 he became F.R.S., and became, in 1760, assistant physician at St. Thomas's Hospital. In 1763 he was elected physician to the Charterhouse, and also became fellow of the College of Physicians. He died of fever at the Charterhouse 5 Nov. 1764.

The fifty-fourth volume of the 'Philosophical Transactions' contains an account, which Hadley drew up, of 'a mummy inspected in London in 1763,' communicated to Dr. William Heberden. This paper was read 12 Jan. 1764, and on 2 Feb. 'he presented to the society an elegant drawing of the left foot of the society's mummy, the sole of the foot, with the bulbous root applied to it, being presented to the view.' He is mentioned in the 'Gentleman's Magazine' (1814, pt. i. p. 427) as an intimate friend of the poet Gray. Dr. Plumptre, president of Queens' College, in recording the vacancy of the fellowship caused by his death, adds: 'He was an ingenious, worthy, and agreeable man, and died much lamented by all that knew him.' There is a portrait of Hadley, engraved after his death in mezzotint by Fisher, from a painting by B. Wilson, dated 1759.

[A Biographical Account of John Hadley, esq., V.P.R.S., the Inventor of the Quadrant, and of his brothers George and Henry (no date); Munk's Coll. of Phys. 1878, ii. 259.]

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