Pierre Simon, Marquis de Laplace (1749-1827), French mathematician and astronomer. Although from a poor family, Laplace's talent led him to become an assistant of the French chemist Lavoisier. He is better known as a talented mathematician and he mainly applied his skills to astronomical problems. Between 1799 and 1825 he collaborated with the French mathematician Lagrange, publishing Mecanique Celeste. The aim of the book was to improve the understanding of the motions in the Solar System by studying the gravitational perturbations between the Sun and the planets. In 1796 Laplace proposed that the Solar System was formed from a rotating disk of gas.