Armand-Hippolyte-Louis Fizeau

Born Sept. 23, 1819, in Paris; died Sept. 18, 1896, at the Château de Venteuil in Seineet-Marne Department. French physicist. Member of the Académic des Sciences (1860).

After graduating from college in Paris, Fizeau attended lectures given by D.-F. Arago and H. Regnault at the Ecole Polytechnique and studied the natural sciences without academic supervision. He was a professor at the Ecole Polytechnique in Paris from 1865 to 1867. He financed most of his own experiments.

Fizeau’s main works dealt with optics. Between 1844 and 1847, Fizeau, together with J.-B.-L. Foucault, detected Fraunhofer lines in the infrared region of the solar spectrum and proposed a method of observing interference at large path differences. In 1848, Fizeau showed how the Doppler effect could be used to measure the relative velocity of stars in the line of sight from the line shifts in the spectra of the stars. In 1849 he devised a method, called the Fizeau method, of determining the speed of light by experiments carried out on the earth’s surface. By means of the Fizeau experiment, he determined the effect of the motion of a medium on the speed of light in the medium. The results of the Fizeau experiment played an important part in the development of the electrodynamics of moving media. Fizeau devised interference methods of measuring the expansion coefficients of solids and determining the angular diameters of stars.

In 1875, Fizeau was elected a foreign member of the Royal Society of London.