Léon Foucault

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The physicist who demonstrated the Earth's rotation with a pendulum in 1851, discovered eddy currents, and gave the gyroscope its name.

The pendulum is what he is remembered for and the eddy currents are what the industry actually pays for. Currents induced in a conductor by a changing magnetic field are the loss that every transformer and motor is designed to minimise, and the effect that induction heating, metal detectors and magnetic braking are designed to exploit - the same phenomenon counted as waste in one application and as the product in another. He also belongs to a pattern this catalogue keeps finding: he built his own instruments, including the knife-edge test still used on telescope mirrors, and people who make their own tools tend to see what the users of those tools cannot.

Also known as: foucault, foucault pendulum, eddy currents, gyroscope

Sources

Léon Foucault, 18 September 1819 to 11 February 1868, French physicist at the Paris Observatory: inventor of the Foucault pendulum demonstrating the Earth's rotation in 1851, an early measurement of the speed of light, the discovery of eddy currents, and credited with naming the gyroscope; Copley Medal 1855, Fellow of the Royal Society 1864

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