D'ALEMBERT, JEAN LE BOND (cid lon-bar'), a French mathematician and encyclopmdist; born in Paris, Nov. 16, 1717; was the natural son of Madame de Tencin and the Chevalier Destouches; and was brought up by the wife of a poor glazier; but his father, without publicly acknowledging the paternity, secured to him an allowance of 1,200 francs a year. At 12 the boy entered the College Ma zarin, where he soon showed his lifelong passion for mathematical studies. His first distinction was admission at 23 to the Academy of Sciences. Two years later appeared his "Treatise on Dynam ics," which reduces all the laws of motion to the consideration of equilibrium, by marking an epoch in mechanical phi losophy. Later works were : "General Cause of Winds," which gained the prize of the Academy of Berlin, 1746, and which contains the first conception and use of the Calculus of Partial Differ ences; "Equilibrium and Movement of Fluids" (1744) ; "Precession of the Equi noxes and Change of the Axis of the Earth" (1749) ; and "The Several Im portant Points in the System of the World" (1754). His "Mathematical
Works" (8 vols. 1761-1780) contain an immense number of memoirs, some on new subjects, some containing develop ments of his previous works.
D'Alembert did not confine himself to physical science. For the great "Ency clopedia" planned by Diderot he wrote the famous "Preliminary Discourse," a noble tribute to literature and philos ophy. Besides numerous articles in the "Encyclopedia" (the mathematical por tion of which he edited), he published books on philosophy, literary criticism, the theory of music, and a treatise "On the Destruction of the Jesuits" (1765), which involved him in controversy. He became secretary to the Academy in 1772, and thereafter he wrote the lives of all the members deceased between 1700 and that year—one of the most pleasing of his works. His literary works have been published by Bossange (5 vols., 1821). He died Oct. 29, 1783.