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Jean le Rond d'Alembert

Jean le Rond d'Alembert, pastel by
Jean le Rond d'Alembert, pastel by Maurice Quentin de la Tour

Jean Le Rond d'Alembert (November 16, 1717October 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 did not 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 submitted 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. He also wrote about what is now called D'Alembert's paradox: that the force on a body immersed in an inviscid fluid is identically zero.

While he made great strides in mathematics and physics, d'Alembert is also famously known for incorrectly arguing in Croix ou Pile that the probability of a coin landing heads increased for every time that it came up tails. In gambling, the strategy of decreasing ones bet the more one wins and increasing one's bet the more one loses is therefore called the d'Alembert system , a type of martingale.

D'Alembert died in Paris in a Duel.

In France, the fundamental theorem of algebra is known as the d'Alembert/Gauss theorem.

See also D'Alembert's principle.


With Denis Diderot, d'Alembert edited a groundbreaking encyclopedia.


  • Jean d'Alembert by Ronald Grimsley. (1963)

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Last updated: 05-07-2005 04:25:38
Last updated: 05-13-2005 07:56:04