LAPLACE, PIERRE SIMON, MARQUIS DE French mathematician and astronomer, was born at Beaumont en-Auge, in Normandy, on March 28, 1749. His father was a small farmer and Laplace owed his education to the interest taken in him by some rich neighbours. He attended the military school at Beaumont, where he became mathematical teacher. In 1767 he went to Paris with letters of recommendation and ap proached D'Alembert, who was then at the height of his fame.
These producing no result, he wrote a letter on the principles of mechanics which evoked the reply : "You needed no introduction, you have recommended yourself ; my support is your due." Ac cordingly D'Alembert obtained for him an appointment as pro fessor of mathematics at the Ecole Militaire in Paris. Laplace had a mastery of analysis, which he proceeded to apply to problems in celestial mechanics. In a paper read before the Academy of Sciences on Feb. 1 o, 1773 (Mem. presentes par divers savants, tom. vii.) he announced the invariability of planetary mean. motions. This was the first step in the establishment of the sta bility of the solar system. It was followed by a series of pro found investigations, contributed by Laplace and Lagrange alter nately, and ending in a brilliant memoir by Laplace (in three parts, vols. of the Academy, 1784-85-86). In various memoirs he demonstrated the cause of the long inequality of Jupiter and Saturn; completed the theory of the Jovian system; and an nounced the dependence of the lunar acceleration on the secular changes in the eccentricity of the earth's orbit.
The time had now come when the work of three generations of illustrious mathematicians on gravitation could be systematized. Laplace devoted himself to this task and produced his famous Mecanique celeste (5 vols., 1799-1825), a monument of mathe
matical genius. The declared aim of the author was to offer a complete solution of the mechanical problem presented by the solar system., In 1796 he published Exposition du systeme du monde, a more popular work; the summary of astronomical his tory with which it ends being one of the masterpieces of the French language. Laplace's nebular hypothesis made its ap pearance in a note in this work.
Laplace studied the figure of equilibrium of a rotating fluid mass, his first memoir on this subject being communicated to the Academy in 1773 and the last in 1817. The results of these papers are embodied in the Mecanique Celeste. In a celebrated memoir, "Theorie des attractions des spheroids et de la figure des planetes" (published in Paris, Memoirs, 1785), he gave a complete solution of the general problem of the attraction of a spheroid on an external particle, and introduces the potential function and Laplace's coefficients. (See SPHERICAL HARMONICS.) Laplace also displayed his genius in the theory of probabilities, publishing in 1812 his Theorie analytique des probabilites, and in 1814 Essai philosophique, a more popular exposition on the same subject.
He received many honours from various scientific societies, and during his later years retired to Arcueil where he was visited by distinguished people from all parts of the world. He died on March 5, 1827.
His complete works were published by the French Government: Oeuvres completes de Laplace (7 vols., • A second edition con taining additional matter was completed in 1912.