Jean le Rond d'Alembert

Born on November 16, 1717, in Paris, the illegitimate son of Madame de Tencin and the artillery officer Louis-Camus Destouches, the newborn child was abandoned on the steps of the church of Saint-Jean-le-Rond, from which he took his name. Rescued by his father and raised by a humble glassmaker's wife, Madame Rousseau—with whom he lived devotedly for nearly fifty years—d'Alembert received an exceptional education at the Jansenist Collège des Quatre-Nations, studying law and medicine before surrendering completely to mathematics. In 1743, at age twenty-five, he published his foundational 'Traité de dynamique', introducing d'Alembert's Principle, which reduced the complex dynamics of accelerating bodies to static equilibrium through the concept of inertial forces. In 1747, while analyzing vibrating strings, he formulated the wave equation and d'Alembert's formula, establishing the mathematical foundations of mathematical physics and partial differential equations. In 1745, d'Alembert joined Denis Diderot to create the monumental 'Encyclopédie, ou dictionnaire raisonné des sciences, des arts et des métiers'. D'Alembert authored the famed 'Discours préliminaire' (Preliminary Discourse, 1751)—a masterwork of Enlightenment epistemology tracing the genealogy of human knowledge through memory, reason, and imagination—as well as over a thousand articles on mathematics and physical sciences. A member of the French Academy from 1754 and its permanent secretary from 1772, d'Alembert was a close friend and intellectual sparring partner of Voltaire. He died in Paris on October 29, 1783, immortalized as one of the chief architects of the Age of Reason.