How many things can be named after one person? In some cases, a huge number of physical things like roads, bridges, and monuments, but let’s instead concentrate on cases where each thing is different. I think a good candidate for the champion of that category is Jean le Rond d’Alembert, who was born November 16, 1717 in Paris. He became a mathematician, a physicist, a music theorist, and something that used to be called a “mechanician,” which was a sort of physicist concentrating on force and motion.
D’Alembert had a difficult start in life. When he was just a few days old, he was left on the steps of a church. That sort of thing was not unheard of, and there was even a tradition about it; the baby was named “le Rond” after the patron saint of the church. Although he was placed into an orphanage, his parents are now actually known; his father was a “chevalier,” sort of a knight, and fairly wealthy. He found the baby in the orphanage, moved him to the home of a family named Rousseau, and supported him (including private school), but since he wasn’t married to the baby’s mother, kept his parentage secret.
It’s not clear whether d’Alembert himself knew his father, but if he did he kept the secret. At school he excelled as a student, and started doing original math by the time he was just 21. He was still living with Madame Rousseau — in fact he stayed in her household for nearly 50 years — but she wasn’t very encouraging. He wrote later that whenever he told her about some new discovery or formulation she’d say something like: “You will never be anything but a philosopher—and what is that but an ass who plagues himself all his life, that he may be talked about after he is dead.” Evidently he didn’t take her comments to heart.
And back to the things named after him. He became a preeminent mathematician and scientist, published widely (over 1,000 articles), and is still known for the d’Alembert…criterion, force, operator, reduction, system, formula, equation, functional equation, paradox, principle, theorem, and “form of the principle of virtual work,” as well as the d’Alembert-Euler condition, the Tree of Diderot and d’Alembert, and the d’Alembert/Gauss theorem. Frederick the Great of Prussia proposed naming a moon of Venus “d’Alembert,” but d’Alembert refused. That was a good idea; it turned out there wasn’t any such moon. But in South Australia Ile d’Alembert is really there. It’s a small island that’s now a conservation area, and also known as Lipson Island.
