Fizeau, Armand Hippolyte Louis (ärmäNˈ ēpôlētˈ lwē fēzōˈ) [key], 1819–96, French physicist. The first to measure (1849) the velocity of light in air, he also determined its speed in water. He made valuable discoveries on the polarization of light and the expansion of crystals, explained the Doppler effect, and devised a method of increasing the permanency of daguerreotypes. With Léon Foucault he took the first clear photograph of the surface of the sun.
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