Jean Bernard Léon Foucault (UK: FOO-koh, US: foo-KOH, French: [ʒɑ̃ bɛʁnaʁ leɔ̃ fuko]; 18 September 1819 – 11 February 1868) was a French physicist best known for his demonstration 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.