Pendulum

In 1851 French physicist Léon Foucault used, for the first time, a pendulum consisting of a brass-coated lead ball hanging from the ceiling by a long cable to show that the Earth rotates on its axis. Once set in motion, momentum caused it to swing back and forth. A stylus under the sphere inscribed its passage on a bed of sand. After a few minutes, "x" patterns appeared in the sand, but the pendulum's trajectory did not vary: the conclusion could thus be drawn that the Earth rotates. Foucault performed the experiment in the cellar of his house before presenting it at the Pantheon. A second ball, made of iron, was used at the Palace of Industry during the 1855 Universal Exhibition. Both spheres have been at Arts et Métiers since 1869.