Laplace, Pierre Simon, Marquis de (1749-1827), the Newton of France, was a native of Beaumont-en-Auges, in Normandy. His abilities gained him the help of some neighbours of position, and at the age of eighteen he went to Paris with letters of introduction to D'Alembert. A letter to the philosophe on the principles of mechanics gained for Laplace his life-long support. The immediate result was an appointment as professor of mathematics at the Ecole Militaire. In 1773 he read a paper before the Academie des Sciences, of which he became a full member in 1785, in which he demonstrated the invariability of planetary mean motions. He continued to investigate the subject, upon which also Lagrange was engaged, during the succeeding years, and in 1787 communicated to the Academie in two theorems his discovery of the cause bf the inequalities of Jupiter and Saturn, and in relation, to the former the "laws of Laplace." In the same year he showed the dependence of lunar acceleration upon the secular changes in the eccentricities of the earth's orbit. The Mecanique Celeste, which was further supplemented, and the Exposition du Systeme du Monde (1796), a note to one of the later editions of which contained the nebular hypothesis, formed Laplace's contributions to mathematical astronomy. In the department of pure mathematics he produced a Theorie Analytique des Probabilites (1812-20). Bonaparte made him Minister of the Interior, but was obliged to replace him by his own brother Lucien after six weeks, as he had no business capacity. He was soon, however, made a senator, and in 1803 became Chancellor of the Senate and a Grand Officer of the Legion of Honour. Although he had been made a count by the new emperor, he voted for his deposition in 1814, and was rewarded with a marquisate by the Bourbons in 1817. Ten years later he died at Arcueil.