Page:Popular Astronomy - Airy - 1881.djvu/301

Rh vibration of a pendulum at the top and bottom of a mine be found, the ratio of the force of gravity at the top to that at the bottom may be calculated, and thence the ratio of the mean density of the earth to that of its surface.

This mode of determining the mean density was put in practice by the Astronomer Royal, at the Harton Coal Pit, near South Shields, in the year 1854. The mean density deduced from his observations is 6·565: a value considerably exceeding that found from the Schehallien and Cavendish experiments.