LESLIE, Sir JOHN, a celebrated natural philosopher, was b. in Largo, Fife, April 16, 1766. While a boy, showing a strong bias for the exact sciences, he was sent to St. Andrews university in 1779. In 1785 lie entered the Edinburgh divinity hall, but devoted most of his time to the sciences, particularly chemistry. In 1788 he left Edin burgh, and after being two years in America, as tutor to the sons of a Virginian planter, he returned to London in 1790. From that time till 1805 he was employed as tutor to the family of Mr. Wedgewoodt at Etruria, Staffordshire, in traveling on the continent, in contributing to the press, and in making experimental researches: the fruits of his labors were a translation of Buffon's Natural Ilis.tory of Birds (1793), the invention of a differential thermometer, a hygrometer, and a photometer, and the publication of an Experimental Inquiry into the Nature and Propagation of Heat (1804), a most ingenious work, constituting an era in the history of that branch of physical science, and for which the royal society awarded him the Rumford medals. In Mar., 1805, be was, after a great deal of opposition from the Edinburgh clergy, elected professor of mathematics in the university of Edinburgh, and soon after commenced the publication of his Course of .ifuthematics. In 1810 Leslie invented the process of artificial congelation, performed
the experiment in the folloiving year before the royal society of London, and in 1813 published a full explanation of his views on the subject ; subsequently be discovered a mode of freezing mercury: In 1819 he was transferred to the chair of natural philoso phy, a position better adapted to his peculiar genius, and in 1823 published one volume of Elements of Natural Philosophy, never completed. In 1832 he was created a knight of the Guelphic order; and on Nov. 3 of the same year expired at Coates, a small estate which he had purchased near Largo. Besides the instruments above mentioned, lie invented an cethrioscope, gyroscope, and atmometer, and contributed many articles to various periodicals on heat, light, metcorolog , the theory of compression, electricity, atmospheric pressure, etc. His last .important work was his discourse on the Progress of Mathematical and Physical Science during the Eighteenth Century, which constitutes the fifth dissertation in the first volume of the Encyclopadia Britannica, 7th and 8th editions.