Sir John Leslie, a Scottish mathematician, born at Largo, Fifeshire, April 16, 1766, died at Coates, in the same county, Nov. 3, 1832. He was educated at the universities of St. Andrews and Edinburgh, and while a student in the latter institution was employed by Adam Smith as tutor to his nephew, afterward Lord'Reston. In 1788-'9 he was absent in America as tutor to two young Virginians of the Randolph family; and in 1790 he went to London, intending to establish himself there as a lecturer on natural philosophy. Disappointed in this project, he translated Buffon's "Natural History of Birds," published in 1793 in 9 vols. Subsequently he travelled in the capacity of tutor to Thomas Wedgwood, and, after being an unsuccessful candidate for professorships at St. Andrews and Glasgow, obtained in 1805 the chair of mathematics in Edinburgh. In 1819 he succeeded Prof. Play-fair in the chair of natural philosophy, which he filled until his death, a few months previous to which he was knighted. His scientific publications commenced with an " Essay on the Resolution of Indeterminate Equations," printed in the " Edinburgh Philosophical Transactions" for 1788; and in 1799 he contributed a description of a hygrometer and photometer invented by himself to Nicholson's "Philosophical Journal." His "Experimental Inquiry into the Nature and Propagation of Heat," published in 1804, gained him the Rum-ford medal of the royal society.

His " Course of Mathematics" (2 vols. 8vo, 1809-'22) comprises "Elements of Geometry," "Geometrical Analysis," "Plane Trigonometry," and "Geometry of Curve Lines;" an abridgment of a portion of this work was published in 1828, entitled "Rudiments of Plane Geometry, including Geometrical Analysis and Plane Trigonometry." He also published in 1817 "The Philosophy of Arithmetic," founded upon an article contributed to the "Encyclopedia Bri-tannica." In 1810 he discovered the process of artificial congelation, by which he was enabled to freeze water and even mercury at pleasure, and three years later published in connection with the subject " A Short Account of Experiments and Instruments depending on the Relations of Air to Heat and Moisture." He also produced " Elements of Natural Philosophy," vol. i., "Mechanics and Hydrostatics" (1823; 2d ed., enlarged, 1829); and "The Progress of Mathematical and Physical Science during the Eighteenth Century," one of the preliminary dissertations of the " Encyclopaedia Britannica."