Foucault's Pendulum lecture. This lecture, 'On the Rotation of the Earth', was delivered at the Royal Institution, London, in 1851 by the British mathematician and Savilian Professor of Geometry Baden Powell (1796-1860). This lecture was one of many prompted by the initial demonstration of Foucault's Pendulum, carried out in Paris, France, in February 1851, by French physicist Leon Foucault (1819-1868). The experiment involves a heavy pendulum swinging on a long arm. The vertical plane in which the pendulum swings rotates with time due to the Earth's daily rotation. Only part of the full circular rotation is shown here.