Laplace, Pierre Simon, Marquis de

Laplace, Pierre Simon, Marquis de (1749-1827), French astronomer and mathematician, best known for his successful application of Newton's theory of gravitation to account for all planetary motion in the solar system. Laplace was born in Normandy and educated at the military school in Beaumont. In 1767 he became Professor of Mathematics at the École Militaire in Paris and in 1785 he was elected to the Academy of Sciences.

Laplace's great work was done in developing the mathematical analysis of the system of gravitational astronomy worked out by Sir Isaac Newton, English mathematician, physicist, and astronomer. Laplace proved that planetary motions are stable, and that perturbations produced by the mutual influence of the 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 (see Cosmology). In Traité de mécanique céleste (Treatise on Celestial Mechanics, 5 vols., 1799-1825) Laplace systematized all the mathematical work that had been done on gravitation. Exposition du système du monde (Explanation of the World System, 1796) contains a summary of the history of astronomy. He also worked on the theory of probability in his Théorie analytique des probabilités (Analytical Theory of Probability, 1812) and Philosophical Essay on Probabilities (1814; trans. 1905).