1819-1868

French physicist who demonstrated the earth's rotation using a pendulum. Foucault made important discoveries in many areas, including the understanding of crystals, inventing the gyroscope (used in inertial navigation systems today), and better processes for silvering telescope mirrors. Foucault's most famous discovery, however, was the pendulum named after him. Attached to a nearly frictionless pivot, the Foucault pendulum swings in a constant plane while the earth rotates beneath it, making the plane of the pendulum seem to rotate.