John Playfair, a Scottish natural philosopher, born at Benvie, Forfarshire, March 10, 1748, died in Edinburgh, July 19, 1819. He was sent at the age of 14 to the university of St. Andrews to be educated for the Scottish church. Here he was occasionally selected by Prof. Wilkie to lecture to his classes on natural history. On the death of his father in 1772 he entered the ministry, and in 1773 he obtained his father's living of Benvie. In 1779 his "Essay on the Arithmetic of Impossible Quantities" was published in the 68th volume of the " Philosophical Transactions." In 1782 he resigned his living to become a private tutor; and in 1785 he became assistant professor of mathematics with Dr. Adam Ferguson in the university of Edinburgh. In 1805 he was appointed general secretary of the Edinburgh royal society, and in the same year became professor of natural philosophy. His literary productions comprise contributions to the "Transactions of the Edinburgh Royal Society" and the "Edinburgh Review," and a number of separate publications, of which a collected edition appeared in 1822 (4 vols. 8vo, Edinburgh). In 1795 appeared his well known edition of Euclid, under the title "Elements of Geometry," prepared for his university classes; in 1802 his "Illustrations of the Huttonian Theory of the Earth," and in 1812-'16 his "Outlines of Natural Philosophy" (2 vols. 8vo), containing the substance of his lectures.

In 1815-'16 he made an extensive geological tour in France, Switzerland, and Italy, to procure materials for an enlarged edition of the " Illustrations," which he did not live to complete. His last important work was a " Dissertation on the Progress of Mathematical and Physical Science," prepared for the " Supplement to the Encyclopaedia Britannica," and left by him incomplete.