Alembert, Jean le Rond d' (zhäN lərôNˈ däläNbĕrˈ) [key], 1717–83, French mathematician and philosopher. The illegitimate son of the chevalier Destouches, he was named for the St. Jean le Rond church, on whose steps he was found. His father had him educated. Diderot made him coeditor of the Encyclopédie, for which he wrote the "preliminary discourse" (1751) and mathematical, philosophical, and literary articles. Discouraged, however, by attacks on his unorthodox views, he withdrew (1758) from the Encyclopédie. A member of the Academy of Sciences (1741) and of the French Academy (1754; appointed secretary, 1772), he was a leading representative of the Enlightenment. His writings include a treatise on dynamics (1743), in which he enunciated a principle of mechanics known as D'Alembert's principle; a work on the theoretical and practical elements of music (1759); and a valuable history of the members of the French Academy (1787).
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