Mathematical and physical astronomer, b. in Beaumont-en-Auge, near Caen, department of Calvados, France, in March (dates given 28, 25, 23, 22), 1749; d. in Paris, 5 March, 1827. The son of a small farmer, he became connected with the military school of his town, first as pupil, then as teacher. At the age of eighteen he went to Paris, and, after convincing d'Alembert of his talents by a letter on the principles of mechanics, obtained a professorship at the military school of the capital. Later he became examiner of the royal artillery (1784) and professor at the Ecole Normale. During the political changes in France he sought favour with Revolution, consul, emperor, and king. In 1799 he accepted from the consul the post of minister of the interior, but, after six weeks, was removed for administrative incapacity. He was a member and even chancellor (1803) of the Senate, and great officer of the Legion of Honour and of the new Order of Reunion. After the downfall of Napoleon (1814) he was nominated Peer of France, with the right of a seat in the Chamber, and in 1817 was raised to the dignity of marquis. His last years were spent in his villa of Arcueil, which became a centre of learned visitors and studious young men (Biot, Poisson, etc.). The Société d'Arcueil was founded with his co-operation. Whereas he remained in undisturbed friendship with his great scientific rival Legrange, other scientists, like Young and Legendre, complained of him for not acknowledging their work. Laplace married at the age of thirty-nine, and a son was born to him in 1789. His scientific discoveries were made between the twentieth and fortieth years of his life. The succeeding thirty-eight years were spent in composing the immortal works: "The System of the World" (1796) and the "Mechanics of the Heavens" (1799-1825).

Analysis owes to Laplace mainly the full development of the co-efficients, of the potential and of the theory of probabilities. In the line of celestial mechanics his glory was made by the discovery (announced in 1773) of the invariability of the planetary mean motions and the consequent stability of the solar system. The "Exposition du Système du Monde", in which the results are presented without mathematical deductions, showed such linguistic excellence that it secured him a seat among the Forty of the French Academy (1816) and for a time the presidency of that body (1817). The five volumes of the "Mécanique Céléste" made him the Newton of France. He was admitted to the French Academy of Sciences, first as associate (1773) and then as member (1785), and took a prominent place in the Institute, into which the Academy developed (1796). He was one of the founders of the Bureau of Longitudes and for a while its president. The Royal Society of London and the principal academies of Europe honoured him with membership. Great scientists, like Berthollet, Cuvier, Humboldt, dedicated their works to him. The collected works of Laplace were printed twice: by the Government in seven volumes (1843-47), the Chamber granting forty thousand francs; and again, at the expense of General Laplace (who left seventy thousand francs for the purpose) and his niece the Marquise of Colbert, in thirteen volumes (1878-1904), under the auspices of the Academy of Sciences. An English translation of the "Mécanique Céléste" by Dr. Bowditch appeared in Boston (1829-39) in four volumes.

Laplace was born and died a Catholic. It has been asserted that to Laplace the Creator was an hypothesis. The origin of this assertion lies in the misinterpretation of a passage of the "Système du Monde" (Oeuvres, VI, 1835, p. 480), where it is evident that by "vain hypotheses" Laplace meant the Deus ex machina of Newton and the "perpetual miracle" of Leibniz's Harmony. It is true that Laplace indulges in a frivolous remark against Callistus III both in the "Theory of Probabilities" (Introduction, also separately as "Essai Philosophique") and in the "System of the World" (IV, iv). He partly atoned for it by omitting the remark in his fourth edition of the "Essai". Death prevented him from doing the same in the sixth edition of the "Système du Monde", the correcting of which he had commenced during his last illness. He died at his home in Paris, Rue du Bac, attended by the curé of the Foreign Missions, in whose parish he was to be buried, and the curé of Arcueil, whom he had called to administer the last comforts of religion (de Joannis, p. 27).

POISSON, Discours pononcé aux Obsèques de M. le Marquis de Laplace in Connaissance de Temps pour l'an 1830; FAYE,Sur l'Origine du Monde (Paris, 1884); DE JOANNIS, Formation Mécanique du Système du Monde (Amiens, 1897), reprinted from Etudes, LXXI (Paris, 1897); FOURIER, Eloge historique de Laplace in Mèmoires de l'Acadèmie des Sciences (Paris, 1831).

John G. Hagen.