LESLIE, Sir JonN (1766-1832). A British natural philosopher and mathematician. He was horn in Largo, Fife, and was educated at Saint Andrews University. In 1785 he entered the Edinburgh Divinity Hall. but devoted much of his time to the sciences, particularly chemistry.
In 1788 he left Edinburgh, having given up all idea of following the Church, and after being two years in America as tutor to the of a Virginia planter, he returned to London in 1790. From that time till 1805 he was employed in private teaching, traveling, writing, and making experimental researches. His most important work during this period was a translation of Ituffon's Natural History of Birds (1793), the invention of a differential thermmeter, a hy grometer, and a photometer, and the publication of an Experimental Inquiry into the Nature and Propagation of Heat (1804). in which were con tained his discoveries in the radiation of heat. For this research lie became noted. and the Roval Society awarded him the Rumford medals. In
March, 1805, after much opposition from the Edinburgh clergy, he was elected professor of mathematics in the University of Edinburgh, and soon after commenced the publication of his Course of Mathematics. In 1810 Leslie invented the process of producing cold artificially and froze water by using an air-pump and acid. (See LIQUEFACTION OF GASES.) In 1813 he published a full explanation of his views on the subject; subsequently he discovered a method of freezing mercury. In 1819 he was transferred to the chair of natural philosophy, a position better adapted to his peculiar genius, and in 1823 published one volume of Elements of Nat ural Philosophy, never completed. In 1832 lie was knighted, and on November 3d of the same year died at Coates, a small estate which lie had purchased near Largo. Besides .the instru ments above mentioned, he invented an :rthrio scope, a pyroscope, and an atmometer.