Pierre Simon Laplace (28.03.1749-5.03.1827) was a French astronomer, physicist and mathematician and a member of the Paris Academy of Sciences (1785). He was born in Beaumont-en-Auge. He studied at a Benedictine school. In 1771 he became professor at the Military School in Paris, and in 1790 chairman of the Chamber of Weights and Measures. He took an active part in the reorganisation of the system of higher education in France, in particular in the creation of the École Normale and the École Polytechnique.
His main work was in celestial mechanics, in which he achieved outstanding results, summed up in the five-volume “Treatise on Celestial Mechanics” (1798 — 1825). He did almost everything his predecessors had been unable to do to explain the motion of the bodies of the Solar System on the basis of the law of universal gravitation. He solved difficult problems of the motion of the planets and their satellites and of the Moon, worked out the theory of the perturbations of celestial bodies, proposed a new way of calculating their orbits, proved the stability of the Solar System over a very long period of time and discovered the cause of the acceleration in the motion of the Moon. He proposed (1796) a hypothesis of the origin of the Solar System.
His research in physics was in the field of molecular physics, heat, acoustics, electricity and optics. In 1821 he established the law of the variation of the density of air with height (the barometric formula). In 1806—07 he worked out the theory of capillarity, using for the first time the idea that molecular attraction makes itself felt only at small distances, and gave a formula for determining capillary pressure (the Laplace formula). He derived (1816) the formula for the speed of sound in gases with a correction for adiabaticity. Together with A. Lavoisier he was the first to use a telescope to measure the linear expansion of bodies, and with the ice calorimeter they constructed he determined (1783) the specific heat capacities of many substances. He was an active opponent of the phlogiston hypothesis. He gave the Biot–Savart law its general form in electrodynamics. As chairman of the Chamber of Weights and Measures he actively put the new metric system of measures into practice.
In the philosophy of natural science he held the positions of spontaneous materialism, and his views were close to those of the French materialists. In mathematics he is known for the Laplace operator, the Laplace transform, the Laplace integral, Laplace's equation and Laplace's theorem, and he is one of the creators of the theory of probability.
A member of the St Petersburg Academy of Sciences (1802).