LAPLACE, PIERRE-SIMON. – Astronomer and mathematician, b. at Beaumont-en-Ange (Calvados) on 23 March 1749, d. in Paris on 5 March 1827. He began his teaching career at the School of Artillery and at the École normale. Having won Bonaparte’s favor, he was first Minister of Public Education and then a senator. Compliant with circumstances, as soon as the Restoration took place he paid homage to Louis XVIII and was elected a member of the Académie française.
His scientific activity began with a study of the mutual perturbations between Jupiter and Saturn; this was followed by research on the secular acceleration of the moon, the discovery of the secular invariability of the mean distances of the planets, and the discovery of important theorems on determinants. He studied the attraction between spheroids, making use of the research he had conducted on the partial differential equation ΔV = 0, which took his name, and was the first to use the method of perturbations, still so fruitful today, which consists in solving a problem in two stages: first, to a first approximation, abstracting from elements of lesser importance, and subsequently, to a second approximation, bringing into play the elements previously disregarded.
L. published in 1796 the Exposition du système du monde, known as the theory of Kant and L., on the formation of the universe; now superseded, but nevertheless far from being concluded. In 1812 he wrote the Théorie analytique des probabilités, which is perhaps the first systematic treatise on this important and delicate subject.
He was a believer, as may be inferred from a letter of 1809 addressed by him to his son, in which he writes: «Je prie Dieu qu'il veille sur tes jours. Aie-Le toujours présent à ta pensée ainsi que ton père et ta mère», and from his Christian death. His complete works were published in 7 vols., in Paris 1843–47, and in 13 vols., ibid. 1878–1904.