Jean Le Rond d’Alembert

Jean le Rond d'Alembert was a French mathematician, mechanician, physicist, and philosophe whose work helped shape both eighteenth-century mathematics and the French Enlightenment. He was born on November 16, 1717, in Paris, France, and died on October 29, 1783, in the same city.

He was the illegitimate son of the writer Claudine Guérin de Tencin and the chevalier Louis-Camus Destouches. Abandoned on the steps of the Saint-Jean-le-Rond chapel beside Notre-Dame de Paris, from which he took his given names, he was raised by a glazier's wife, Madame Rousseau, with whom he lived for nearly fifty years. Destouches paid for his education at the Collège des Quatre-Nations.

D'Alembert's 1743 Traité de dynamique stated what is now called d'Alembert's principle, recasting the laws of motion in a form that simplified problems of constrained mechanics. He went on to study fluid dynamics, the precession of the equinoxes, and the wave equation, and he made early contributions to the theory of partial differential equations and to limits in the foundations of calculus.

From 1751 he served, with Denis Diderot, as co-editor of the Encyclopédie, the great Enlightenment reference work. His Discours préliminaire to the first volume mapped the relations among the sciences and the arts and became a manifesto of philosophical method. He withdrew as editor in 1759 after political pressure but continued to contribute mathematical and scientific articles.

The given name Jean is the French form of John, from the Hebrew Yochanan, meaning God is gracious. He carried it together with le Rond, taken from the chapel where he was found as an infant.