September 15, 1736 – November 12, 1793
Jean-Sylvain Bailly was a French astronomer and orator, one of the leaders of the early part of the French Revolution. He was ultimately guillotined during the Reign of Terror.
Born in Paris, he was originally intended for the profession of a painter, but preferred writing tragedies, until attracted to science by the influence of Nicolas de Lacaille. He calculated an orbit for Halley's Comet when it appeared in 1759, reduced Lacaille's observations of 515 zodiacal stars, and was elected a member of the French Academy of Sciences in 1763. His Essai sur la theorie des satellites de Jupiter (Essay on the theory of the satellites of Jupiter, 1766), an expansion of a memoir presented to the Academy in 1763, showed much original power; and it was followed up in 1771 by a noteworthy dissertation Sur les inegalites de la lumiere des satellites de Jupiter (On the inequalities of light of the satellites of Jupiter). In 1778, he was elected a foreign member of the Royal Swedish Academy of Sciences.
Meantime, he had gained a high literary reputation by his Éloges of King Charles V of France, Lacaille, Molière, Pierre Corneille and Gottfried Leibniz, which were issued in collected form in 1770 and 1790; he was admitted to the Académie française on 26 February 1784, and to the Académie des Inscriptions in 1785, when Bernard le Bovier de Fontenelle's simultaneous membership of all three Academies was renewed in him.
From then on, he devoted himself to the history of science, publishing successively: Histoire de l'astronomie ancienne (A history of ancient astronomy, 1775); Histoire de l'astronomie moderne (A history of modern astronomy, 3 vols., 1779-1782); Lettres sur l'origine des sciences (Letters on the origin of the sciences, 1777); Lettres sur l' Atlantide de Platon (Letters on Plato's Atlantide , 1779); and Traite de l'astronomie indienne et orientale (A treatise on Indian and Oriental astronomy, 1787). The 1911 Encyclopædia Britannica remarks that "Their erudition was… marred by speculative extravagances."
The lunar crater Bailly is named in his honor.