Arago, (Dominique) Fran�ois (Jean) 1786-1853
French scientist and politician

Born in Estagel, in the Pyr�n�es Orientales region, he went to the �cole Polytechnique, Paris, at the age of 17. In 1804 he became secretary to the Observatory and in 1830 its chief director. He took a prominent part in the July Revolution (1830) and as a member of the Chamber of Deputies voted with the extreme left. In 1848 he became a member of the provisional government, but refused to take the oath of allegiance to Napoleon III after the events of 1851-52. His achievements were mainly in the fields of astronomy, magnetism and optics. He developed a polar-imeter, which he used to observe the polarization of cometary light, concluding that comets are not selfluminous, but simply reflect sunlight. Arago encouraged Urbain Jean Joseph Leverrier in his mathematical studies to discover Neptune. He is especially remembered for his great compendium of astronomy, Astronomie populaire ('Popular Astronomy'), which did much to extend the scientific enlightenment of the European middle classes. In studies of magnetism he gave an early demonstration of the magnetic field produced by the flow of an electric current round a conducting coil. He also speculated on the nature of light, propounding first the particle theory and later the wave theory of Augustin Fresnel.