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Britannica Hong Kong > Encyclopedia Categories > Astronomy > Foucault, Jean (-Bernard-Léon)

Foucault, Jean (-Bernard-Léon)

(born Sept. 18, 1819, Paris, France—died Feb. 11, 1868, Paris) French physicist. Though educated in medicine, his interests lay in physics. In 1850 he measured the speed of light with extreme accuracy. He invented the Foucault pendulum and used it to provide experimental proof that Earth rotates on its axis. He also discovered the existence of eddy currents (Foucault currents) in a copper disk moving in a strong magnetic field and invented (1859) a simple but extremely accurate method of testing telescope mirrors for surface defects.

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