Jean le Rond d'Alembert was a mathematician and physicist who applied his considerable genius to solving problems in mechanics. This is the branch of physics that deals with the effect of forces on matter, either at rest or in motion. His most important contribution was d'Alembert's principle, which states that the forces in an object that resist acceleration must be equal and opposite to the forces that produce the acceleration. D'Alembert was a pioneer in the development of calculus. He also served as science editor of Denis Diderot's Encyclopédie.

D'Alembert was born in Paris on November 17, 1717. He was the illegitimate son of Claudine-Alexandrine Guérin, Marquise de Tencin, an intelligent and unprincipled woman who broke her vows as a nun and became the mistress of many powerful men. D'Alembert's father was the Chevalier Louis-Camus Destouches, a military officer. D'Alembert's mother apparently regarded her pregnancy as...