Foucault's measurements of the speed of light

Scientific instrument used to measure the speed of light

In 1850, Léon Foucault used a rotating mirror to perform a differential measurement of the speed of light in water versus its speed in air. Together with a similar measurement by Hippolyte Fizeau, this result confirmed the wave behavior of light. In 1862, Foucault used a similar apparatus to measure the speed of light in the air, obtaining a value within 0.6% of the modern value.

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