French physicist (1819-1868) best known for the invention of the Foucault pendulum, a device demonstrating the effect of the Earth's rotation; he also made an early measurement of the speed of light, discovered eddy currents, and is credited with naming the gyroscope. Untranslated ALS in French, signed “L. Foucault,” one page, 4.75 x 7.25, October 11, 1860. In fine condition.
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