BAILLY, JEAN SYLVAIN French astron omer and orator, was born at Paris on Sept. 15, 1736. He cal culated an orbit for the comet of 1759 (Halley's), reduced Lacaille's observations of 515 zodiacal stars, and was, in 1763, elected a member of the Academy of Sciences. His Essai sur la theorie des satellites de Jupiter (1766), was followed up in 1771 by a dissertation Sur les inegalites de la lumiere des satellites de Jupiter and by a series of important works on the history of science.
The Revolution interrupted his studies. Elected deputy from Paris to the states-general, he was chosen president of the Third Estate (May 5, 1789), led the famous proceedings in the Tennis Court (June 20), and acted as mayor of Paris (July 55 1789, to Nov. 16 1791) . The dispersal by the National Guard, under his orders, of the riotous assembly in the Champ de Mars (July 17 1791), rendered him obnoxious to the infuriated populace, and he retired to Nantes, where he composed his Memoires d'un temoin (published by MM. Berville and Barriere, 1821-22), an incom plete narrative of the extraordinary events of his public life. Late in 1793, Bailly quitted Nantes to join his friend Pierre Simon Laplace at Melun ; but was there recognized, arrested and brought (Nov. 1o) before the Revolutionary Tribunal at Paris. On Nov. 12 he was guillotined.