He was a French astronomer who predicted the existence of Neptune by mathematical means. He worked at the Paris Observatory for most of his life and switched from his first subject chemistry to teach astronomy at the Ecole Polytechnique. His main activity was in celestial mechanics. He calculated the position of Neptune from irregularities in Uranus’ orbit. When he asked the German astronomer Johan G. Galle to look for Neptune, he discovered Neptune after only an hour of searching, within one degree of the position that had been computed by Le Verrier. He gave the most striking confirmation of the theory of gravitation propounded by Newton. He also initiated the meteorological service for France.