Armand Hippolyte Louis Fizeau (September 23, 1819-1896), French physicist, was born in Paris. His earliest work was concerned with improvements in photographic 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 1848, he discovered the Doppler effect for electromagnetic waves. In 1849 he published the first results obtained by his method for determining the speed of light (see Fizeau-Foucault apparatus), and in 1850 with E. Gounelle measured the speed of electricity.
In 1853 he described the employment of the capacitor (then called the condenser) as a means for increasing the efficiency of the induction coil. Subsequently he studied the thermal expansion of solids, and applied the phenomena of interference of light to the measurement of the dilatations of crystals. He died at Venteuil September 18, 1896. He became a member of the Académie française in 1860 and of the Bureau des Longitudes in 1878.