Jean le Rond d'Alembert

Left on the steps of the church of Saint-Jean-le-Rond in Paris in 1717, d'Alembert grew up as the illegitimate son of an artillery officer and a salon hostess. He trained in law, medicine, and finally mathematics, teaching himself analysis from borrowed books.

In 1743 his Traité de dynamique reformulated Newtonian mechanics in terms of what is now called d'Alembert's principle: the force of inertia opposing motion can be treated as a real force, turning every dynamics problem into a statics problem. Three years later, in a memoir to the Berlin Academy, he wrote down the partial differential equation for a vibrating string and proved its general solution is a right-moving plus a left-moving waveform — an insight that would structure the theory of every wave in physics.

He co-edited the Encyclopédie with Diderot, writing its mathematical articles. He fought with Euler, Bernoulli, and Clairaut about everything from the shape of the Earth to the three-body problem. He worked out the precession equations for the Earth's axis. He refused Frederick the Great's offer to preside over the Berlin Academy. He died, respected and tired, in 1783.