Foucault Pendulum
Earth's rotation causes the pendulum's plane to slowly rotate
Léon Foucault (1851, Panthéon, Paris): a 67m pendulum with a 28kg bob. The plane of swing rotates at Ω_eff = Ω_Earth × sin(latitude) rad/s. At the pole it completes a full turn in 24h; at the equator there is no rotation. This was the first direct laboratory proof that Earth rotates. The original Foucault pendulum still hangs in Paris.