Foucault pendulum

Foucault's pendulum in the Panthéon, Paris The Foucault pendulum or Foucault's pendulum is a simple device named after French physicist Léon Foucault, conceived as an experiment to demonstrate the Earth's rotation. If a long and heavy pendulum suspended from the high roof above a circular area is monitored over an extended period of time, its plane of oscillation appears to change spontaneously as the Earth makes its 24-hourly rotation. This effect is greatest at the poles and diminishes with lower latitude until it no longer exists at Earth's equator.

Foucault introduced his pendulum in 1851 in the first experiment to give simple, direct evidence of the Earth's rotation, which he further demonstrated in 1852 with a gyroscope experiment. Foucault pendulums have become popular in science museums and universities.