ARMAND HIPPOLYTE LOUIS FIZEAU (1819–1896), French physicist, was born at Paris on the 23rd of September 1819. His earliest work was concerned with improvements in photo-graphic processes; and then, in association with J. B. L. Foucault, he engaged in a series of investigations on the interference of light and heat. In 1849 he published the first results obtained by his method for determining the speed of propagation of light (see LIGHT), and in 185o with E. Gounelle measured the velocity of electricity. In 1853 he described the employment of the con-denser as a means for increasing the efficiency of the induction-coil. Subsequently he studied the expansion of solids by heat, and applied the phenomena of interference of light to the measurement of the dilatations of crystals. He died at Venteuil on the 18th of September 1896. He became a member of the French Academy in 186o and of the Bureau des Longitudes in 1878.