Jean Bernard Léon Foucault (French pronunciation: ​[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 (although he did not invent it).