Mathematician and French astronomer who developed the celestial mechanics, whose name remains attached to the so-called nebular theory of the origin of the solar system. Made some years before by the German philosopher Emmanuel Kant, who in turn had taken it from an idea of Descartes, the theory proposes that our solar system originated from a gaseous disk in rotation: the Sun was formed in the Center, and the planets in the periphery, by contraction of successive rotating rings. The theory has been recovered in our time, corrected and reformed, and today constitutes the most accredited theory on the origins of our solar system; It is collected in his exposition of the system of the world (1796) volume. He/She demonstrated that gravitational perturbations induced by one planet on the other have no immediate consequence the emergence of irregularities in their orbits, as Newton. He/She also devoted himself to studies of celestial mechanics and, together with Lagrange, was the greatest authority of his century. Between 1799 and 1825 he/she wrote a major work in five volumes, Treaty of celestial mechanics, which incorporated the new theories developed from the works of Newton, as well as their own contributions.