Foucault pendulum, 19th-century illustration. This apparatus was named for French physicist Leon Foucault (1819-1868), who first erected it in 1851. The experiment demonstrated the rotation of the Earth. A pendulum is 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. Famously demonstrated in the Pantheon, Paris, this was the first time the rotation of the Earth could be shown without astronomical observations. Illustration published in 1882.