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Foucault's pendulum. 1902 illustration of the French astronomer Nicolas Camille Flammarion inaugurating Foucault's pendulum in the Pantheon, Paris, France. This apparatus was first erected by the French physicist Leon Foucault (1819-1868) in 1851. The experiment demonstrated the rotation of the Earth. A pendulum, hanging from the Pantheon's ceiling, was allowed to swing free in any vertical plane. The plane in which the pendulum swings rotates with time due to the Earth's daily rotation. This was the first time the rotation of the Earth had been demonstrated without using astronomical observations. The original pendulum was moved in 1855, with a copy installed in the Pantheon since 1995. Image from Le Petit Parisien newspaper, France, 2nd november (KEYSTONE/SCIENCE PHOTO LIBRARY/CCI ARCHIVES/SCIENCE PHOTO LIBRARY)