The French mathematician and encyclopedist Jean Le Rond d'Alembert was the illegitimate son of Madame de Tencin and the artillery general Destouches-Canon. He was abandoned by his mother on the steps of the baptistry of Saint-Jean-Le-Rond in Paris, from which he received his name. Shortly afterward his father returned from the provinces, claimed the child, and placed him with Madame Rousseau, a glazier's wife, with whom d'Alembert remained until a severe illness in 1765 forced him to seek new quarters. Through the Destouches family, Jean Le Rond was placed in the exclusive Jansenist Collège de Mazarin and given the name of d'Aremberg, which he later changed to d'Alembert, no doubt for phonetic reasons. At the college an effort was made to win him over to the Jansenist cause, and he went so far as to write...