Schiehallion Experiment: How Astronomers Weighed The Earth

In the summer of 1774, a team of British astronomers working under the patronage of the Royal Society established camp at the foot of a lonely mountain in the Scottish Highlands to conduct one of the most ingenious scientific experiments of the 18th century. Armed with telescopes, pendulums, quadrants, barometers, and delicate measuring rods, these men were attempting to weigh the Earth.

The mountain they chose was Schiehallion, an isolated peak in Perthshire whose smooth, symmetrical shape made it ideal for the audacious experiment. The project became known as the Schiehallion experiment, and it represented one of the first serious attempts to determine the planet’s mass using Newtonian physics.

The Schiehallion in Perthshire. Credit: Tim Hayes

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