Foucaults gyroscope demonstration apparatus, c 1883.

FRANCE - NOVEMBER 20: Made by Parisian instrument makers Dumoulin-Froment, this apparatus was used to demonstrate the rotation of the Earth. Acquired by the Science Museum in London in 1883, it uses spinning gyroscopes. These devices were first conceived in 1852 by the French Physicist Leon Foucault (1819-1868), following his success, a year earlier, in using a pendulum to detect the Earth�s rotation. In operation, the disc of the gyroscope is made to spin at high speed using the mechanism in the middle. Once spinning, it is transferred to the frame on the right and suspended by a fine silk thread with a thin pointer attached. The subsequent horizontal motion of the gyroscope can then be detected using the fine scale and microscope on the left. (Photo by SSPL/Getty Images)