French physicist. A graduate of the École Polytechnique, professor at the Collège de France, member of the Académie Royale des Sciences of Paris, and astronomer of the Bureau des Longitudes. Researched such topics as double refraction, Fraunhofer lines, and the influence of the Earth's motion on the interference of light. Invented many instruments, including a polariscope, an optical goniometer, and a hygrometer. Prolific author of articles and scientific treatises.