Fizeau, Hippolyte

(1819-1896)

   physicist

   Born in Paris, Hippolyte Fizeau, who was interested in photography with léon FOucAULT,pro-duced a daguerreotype of the surface of the sun (1845). He also put in place the first method (without recourse to astronomical observation) to measure the speed of light. He did this in 1849 by sending a beam of light between gear teeth in the edge of a rotating wheel. The beam then traveled a distance to a mirror and came back to the rapidly spinning wheel, where a tooth would block the light, allowing the speed to be calculated. He brought, too, to optics the effect discovered by Christian Doppler (Doppler-Fizeau effect) in the case of sonar waves, which allow the measurement of the radical speed of stars (he also discovered double stars). Fizeau, who additionally did work on dilatation and the optical properties of solid bodies, was named to the Academy of Sciences in 1860.