Armand Hippolyte Louis Fizeau (1819—1896), French physicist, was born at Paris on September 23, 1819. 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 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 French Academy in 1860 and of the Bureau des Longitudes in 1878.

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The original text for this article was based on the 1911 Encyclopaedia Britannica.