FIZEAU, ARMAND HIPPOLYTE LOUIS (1819 1896), French physicist, was born at Paris on Sept. 23, 1819. As he was wealthy he was able to follow his inclinations and devote himself to experimental work in physics. Between 1845 and he worked in conjunction with Foucault (q.v.). They investigated the infra-red portion of the solar spectrum, and made other ob servations, in heat and light. In 1849 Fizeau published the re sults of his experiments on the velocity of light (q.v.) ; he gave the first reliable value of this velocity by a terrestrial method, and the correct explanation of the Doppler principle (see LIGHT : Waves and Interference), as applied to the light coming from a star (q.v.), and showed how it could be used to measure the rela tive velocities of stars in the line of sight. In 1851 he carried out a series of experiments on the velocity of light in a moving me dium, and measured the shift of interference fringes due to light passing through a column of moving water. These experiments were designed to see if any relative motion of aether and matter could be detected (see ETHER). Later experiments describe the use of a condenser for increasing the efficiency of an induction coil and the application of interference methods for measuring the ex pansion of crystals. He became a member of the French Academy in 186o and of the Bureau des Longitudes in 1878; in 1863 he was appointed inspecteur de physique at the >?cole Polytechnique, Paris. He died at Venteuil on Sept. 18, 1896.