Cavendish experiment

Cavendish's diagram of his torsion pendulum, seen from above. The pendulum consists of two small spherical lead weights (h, h) hanging from a 6-foot horizontal wooden beam supported in the center by a fine torsion wire. The beam is protected from air currents inside a wooden box (A, A, A, A). The two large weights (W, W) attached to a separate suspension attract the small weights, causing the beam to rotate slightly. The rotation is read off of vernier scales (S) at either end of the rod. The large weights can be rotated to the other side of the torsion beam (w, w), causing the beam to rotate in the opposite direction.

The Cavendish experiment, performed in 1797–1798 by English scientist Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory and the first to yield accurate values for the gravitational constant. Because of the unit conventions then in use, the gravitational constant does not appear explicitly in Cavendish's work. Instead, the result was originally expressed as the relative density of Earth, or equivalently the mass of Earth. His experiment gave the first accurate values for these geophysical constants.