Profession: astronomer

Arago taught Le Verrier, and encouraged the mathematical research that led to his prediction of Neptune’s existence. Le Verrier wrote to Galle, who found the planet after an hour’s observation. Adams had reached the same mathematical conclusion earlier but without publishing the results; public controversy over who was first did not stop Le Verrier and Adams becoming good friends. Arago proposed the new planet be named ‘Leverrier’ (sic) before ‘Neptune’ prevailed, Airy having done what he could to dissuade Le Verrier from the idea, which was in fact his own. Babbage was among Le Verrier’s correspondents.

A letter to d’Alembert on mathematical principles got Laplace a professorship at the École Militaire. He taught Fourier (who however thought Lagrange and Monge better teachers), and encouraged Cauchy. Lagrange was a professional rival, but both gained from the mutual flow of ideas. Laplace and Berthollet founded the influential Société d’Arcueil, whose members included Arago, Poisson, Biot, Gay-Lussac, Malus and Humboldt. With Lavoisier, he showed that respiration was a form of combustion. Biot helped prepare his work for publication, but said that Laplace often forgot his original reasoning, substituting the line “it is easy to see.”

Unknown to Adams, Le Verrier had reached the same mathematical conclusions as him about the existence of a new planet (Neptune). Adams had already left a paper with Airy, the Astronomer Royal, asking for observations to be made to test for the predicted planet’s existence, but Airy fatally delayed his response, and when a row erupted over the truth of the discovery of Neptune, cold-shouldered Adams. Le Verrier became a good friend to Adams, despite getting all of the credit. Stokes was a professional collaborator and frequent correspondent; Babbage also corresponded with him.

Bolyai was a fellow-student, and Gauss’s only real friend — they corresponded for life. Humboldt inspired Gauss’s researches into magnetism, and sought his help towards a global grid of magnetic observatories. His collaboration with Weber led to the first electric telegraph. Jacobi’s youthful work impressed him, and Dedekind, Cantor and Riemann were among his students, though he disliked teaching. Dirichlet carried his ‘Disquisitiones Arithmeticae’ with him all his life. Germain (under a male pseudonym) conducted a substantial mathematical correspondence with him: other correspondents included Bessel and Olbers.