Léon Foucault
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Jean Bernard Léon Foucault was a French physicist who invented the Foucault pendulum, a device demonstrating the effect of Earth's rotation. He also made an early measurement of the speed of light, di
Photograph by Bertall & Cie
Grave of Jean Bernard Léon Foucault in Montmartre Cemetery
Speed of light
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The speed of light is the speed of electromagnetic waves. Light travels at slower speed inside materials like glass or water; its highest speed is in a vacuum. The speed of light in vacuum is a univer
Léon Foucault
…a French physicist who invented the Foucault pendulum, a device demonstrating the effect of Earth's rotation. He also made an early measurement of the speed of light, discovered eddy currents, and is credited with naming the gyroscope. The son of a publisher, Foucault was born in Paris on 18 September 1819. After…
One of the last and most accurate time of flight measurements, Michelson, Pease and Pearson's 1930–1935 experiment used a rotating mirror and a one-mile (1.6 km) long vacuum chamber which the light beam traversed 10 times. It achieved accuracy of ±11 km/s.
Hendrik Lorentz (right) with Albert Einstein (1921)