Foucault, Jean Bernard Léon
Jean Bernard Léon Foucault (1819-1868), a French physicist who, in 1850, measured the speed of light within about 0.6% of the currently accepted value. He invented the Foucault pendulum that demonstrates the rotation of the Earth by changing the plane of its oscillation as the Earth rotates underneath it. Foucault also discovered the existence of eddy currents (Foucault currents) in a copper disk moving in a strong magnetic field. In 1859, he invented a simple but extremely accurate method of testing telescope mirrors for surface defects. Foucault also invented the gyroscope, which is essentially a wheel on an axle that resists change in its orientation while spinning. The gyroscope is used to measure orientation based on the principle of conservation of angular momentum.
Further Reading
The Foucault Pendulum (University of New South Wales, School of Physics)
