Jean Bernard Léon Foucault (UK: , US: ; French: [ʒɑ̃ bɛʁnaʁ leɔ̃ fuko]; 18 September 1819 – 11 February 1868) 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, discovered eddy currents, and is credited with naming the gyroscope.