ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY ROYAL ASTRONOMICAL SOCIETY / SCIENCE PHOTO LIBRARY
Gravity experiment, Greenwich, 1888. This reversible swinging pendulum apparatus, in the Safe Room at the Royal Observatory Greenwich, is part of an experiment carried out from 8-14 November 1888 by Commandant Gilbert Etienne Defforges (1852-1915). Defforges, from the Paris Observatory and the geographical section of the French Army, worked from 1884 on using pendulums to determine the intensity of the Earth's gravitational field at different points in western Europe and northern Africa. He carried out 41 determinations at 35 different locations. Gravity can be calculated from the period of oscillations of a pendulum.
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