François Arago, the first to show in 1810 that the surface of the Sun and stars is made of incandescent gas and not solid or liquid, was a prominent physicist of the 19th century. He used his considerable influence to help Fresnel, Ampere and others develop their ideas and make themselves known. This book covers his personal contributions to physics, astronomy, geodesy and oceanography, which are far from negligible, but insufficiently known. Arago was also an important and i