POISSON, SIMEON-DENIS, a celebrated French geometer, was b. at Pithiviers, in the dep. of Loiret„Iune 21,1781; and displaying an aptitude for mathematics, he was received into the &Me polytechnique in 1798. The striking talent he thus early exhibited attracted the notice of Lagrange and Laplace, both of whonl anticipated for him a brill iant future. In 1802 he become a professor in the polytechnique; in 1&08 a member of the bureau des longitudes; in .1809 professor of mechanics to the faculty of sciences; member of the institute in 1812, etc.; and this list of distinctions was crowned in 1837 by his elevation to the dignity of a peer of France. He died in 1840. Poisson's Nvholo life was devoted to the prosecution of scientific research, and the fruits of his pen num ber about 300 memoirs, inserted in the publications of the ecole polytechnique, of the academy of sciences, and other scientific journals. A complete these labors
by Poisson himself is published by Arago (Notices Blographipes, vol. ii.). Of the sep arate treatises published by Poisson, the following are the chief: Traild de Meranique (2 vols.. 1883); Nouvelle Theoric de l'Action Capillaire ; Ththnr•ie Hatiremalique de 14 Clialeur (1835); Memoiresur le Youvement des Projectiles dans lair, eau aslant jgard d la Rotation de la Terre (1839); and lastly, the celebrated work, Sur PInvariabilite des livens Mouve limas des grands Axes Plan6taires. Poisson is fairly considered one of the chief founders of the science of mathematical physics, which was brought by him to great perfection, especially in what concerns statical electricity and magnetism. Many other ingenious discoveries and speculations are dispersed throughout his writings.