Foucault pendulum, 1988.

UNITED KINGDOM - JANUARY 12: Made by Professor Brian Pippard in the workshops of the Cavendish Laboratory in Cambridge, Kent in 1988, this Foucault Pendulum has been demonstrating the Earth�s rotation at the Science Museum since 1988. Unlike its predecessor, this pendulum runs continually, thus avoiding the need to re-swing the pendulum each hour. Gently raising and lowering the pendulum pivot, using a motor in conjunction with a sensor, keeps the pendulum in motion. Known as �parametric amplification�, it uses the same principle which keeps a child�s swing in motion. The French physicist Leon Foucault (1819-1868) conceived the display and first demonstrated it at the Parisian Pantheon in 1851. (Photo by SSPL/Getty Images)