La Place, Pierre-Simon, marquis de

(1749-1827)

   astronomer, mathematician, physicist

   Best known for his successful application of Newton's theory of gravitation to account for all planetary motion, Pierre-Simon, marquis de La Place was born in Beaumont-au-Auge, Normandy. In 1767, he became professor of mathematics at the École militaire in Paris. He entered the Senate in 1799, served as its vice president (1803), and was named a count of the Empire by napoléon i (1806). He later supported King louis XV III, who made him a marquis and peer of France. La Place's most important work in astronomy concerned a study of the movements of Saturn and Jupiter. It was in describing these movements that La Place made his important mathematical discoveries: that planetary motions are stable, and that perturbations produced by mutual influence of planets or by external bodies, such as comets, are only temporary. He attempted to give a rational theory of the origin of the solar system in his nebular hypothesis of stellar evolution. In his Traité de mécanique céleste (five volumes, 1799-1825), he systematized all the mathematical work that had been done on gravitation. His Exposition du système du monde (1796) contained a summary of the history of astronomy. La Place also worked on the theory of probabilities in his Théorie analytique des probabilités (1812). La Place was named to the Academy of Sciences in 1773 and to the Académie Française in 1816.