Jean Le Rond d'Alembert (November 16, 1717 - October 29, 1783) was a French mathematician, mechanician, physicist and philosopher. He was also one of the editors of the Encyclopédie, an early French encyclopedia. D'Alembert's method for the wave equation is named after him.
Born in Paris, d'Alembert was the illegitimate child of the writer Claudine Guérin de Tencin and the chevalier Louis-Camus Destouches (an artillery officer). Destouches was abroad at the time of d'Alembert's birth, and a couple of days after birth his mother left him on the steps of the Saint-Jean-le-Rond de Paris church. According to custom he is named after the protecting saint of the church. d'Alembert was placed in an orphanage but was soon adopted by the wife of a glazier. Destouches secretly paid for the education of Jean le Rond, but didn't want his parentage officially recognised.
D'Alembert first attended a private school. The chevalier Destouches left d'Alembert an annuity of 1200 livres on his death in 1726. Under the influence of the Destouches family, at the age of twelve d'Alembert entered the Quatre-Nations jansenist college (the institution was also known under the name Mazarin). Here he studied philosophy, law, and art, graduating as bachelier in 1735. In his later life d'Alembert scorned the Cartesian principles he had been taught by the Jansenists: "physical premotion, innate ideas and the vortices".
The Jansenists steered d'Alembert toward an ecclesiastical career, attempting to deter him from pursuits such as poetry and mathematics. Theology was, however, "rather unsubstantial fodder" for d'Alembert. He entered law school for two years, and was nominated avocat in 1738.
He was also interested in medicine and mathematics. Jean le Rond was first registered under the name Daremberg, but later changed it to d'Alembert. In July of 1739 he made his first contribution to the field of mathematics, pointing out the errors he had detected in L'analyse démontrée (published 1708 by Charles René Reynaud) in a communication addressed to the Académie des Sciences. At the time L'analyse démontrée was a standard work, which d'Alembert himself had used to study the foundations of mathematics.
In 1740 he submited his second scientific work from the field of fluid mechanics Memoire sur le refraction des corps solides, which was recognized by Clairaut. In this work d'Alembert theoretically explained refraction.