The chief contribution by the French mathematician and physicist Jean le Rond d'Alembert (1717-1783) is D'Alembert's principle, in mechanics. He was also a pioneer in the study of partial differential equations.

Jean le Rond d'Alembert was born on Nov. 16, 1717, and abandoned on the steps of the church of St-Jean-le-Rond in Paris. He was christened Jean Baptiste le Rond. The infant was given into the care of foster parents named Rousseau. Jean was the illegitimate son of Madame de Tencin, a famous salon hostess, and Chevalier Destouches, an artillery officer, who provided for his education. At the age of 12, Jean entered the Collège Mazarin and shortly afterward adopted the name D'Alembert. He became a barrister but was drawn irresistibly toward mathematics.

Two memoirs, one on the motion of solid bodies in a fluid and the other on integral calculus, secured D'Alembert's election in 1742 as a member of...