Foucault's pendulum, named after the French physicist Léon Foucault, was conceived as an experiment to demonstrate the rotation of the Earth. The experimental apparatus consists of a tall pendulum free to oscillate in any vertical plane. The direction along which the pendulum swings appears to rotate with time because of Earth's daily rotation.
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From Wikipedia: This is an animation of a Foucault pendulum at the Pantheon in Paris (48°52' North), with the Earth's rotation rate greatly exaggerated. The green trace shows the path of the pendulum bob over the ground (a rotating reference frame), while the blue trace shows the path in a frame of reference rotating with the plane of the pendulum.