PLAY'FAIR, JOHN (1748-1819). An lish mathematician and geologist, born at Benvie. Be was taught by his father until he was 14 years cf age, when he was sent to Saint Andrews, where he made rapid progress, especially in math ematics and natural philosophy, graduating in 1765. He entered the ministry in 1770, but still devoted his leisure time to mathematical studies, and in 1779 he contributed to the Transactions of the Royal Society a paper the Arithmetic of Impossible In 1785 he became professor of mathematics, jointly with Dr. Adam Ferguson. in the University of Edinburgh. He became secretary of the physical class in the Edinburgh Royal Society in 1789, and later gen eral secretary, which post he held till his death. In 1805 he exchanged the chair of mathematics for that of natural philosophy. In 1807 he be came a fellow of the Royal Society. A few years before his death he traveled through France, Switzerland, and Italy, for the purpose of study ing the geological and mineralogical features of these countries. From 1804 onward he was a
frequent contributor to the Edinburgh Review. Among the subjects reviewed are "_Nudge's Trigo nometrical Survey" (1805) ; "Meehain and De lambre, Base du systeme metrique decimate" (1808) ; "Le Compte rendu par l'Institut de "Lambton's Indian Survey" (1S13) : "Laplace. Essai philosophique sur les probabilit6s" (1S14) ; "Baron de Zach, Attrac tion des montagnes" (ISIC) ; "hater on the Pendulum" (ISIS). AU of these were reprinted in the fourth volume of the collected edition of his works, edited by James 0. Playfair (4 vols., 1s22). lle also contributed several articles to the Encycloiardia Britannica. For the Transac tions of the Royal Society of Edinburgh he wrote among other memoirs: On the Origin and Inves tigations of (1794) ; "On the Trigonom etry of the Brahmins" (1798). He also edited Euclid's Elements (1795), and wrote Outlines of Natural Philosophy (2 vols., 1812-16), and Illustrations of the Huttonian Theory of the Earth.