2-913-906 - The Print Collector/Heritage Images

Mouth of the Harton Coal-Pit, South Shields, 1854. Mr. Airy['s] grand object was to arrive at the weight of our globe...it being necessary to know this before we can proceed to determine the weight or mass of the sun, moon, and planets, which is of the utmost importance to practical astronomy...[in order to] ascertain whether the centre of the globe was a mass of matter, [Mr Airy]...saw that...it would be most easily settled by observing the number of vibrations made by a pendulum swung at the surface of the earth and at the bottom of the deepest mine. The number of vibrations...is a correct measure of the power of gravitation; and, as we penetrate the comparatively light super-strata or crust of the globe, and approach the much denser and heavier mass forming the interior, the attraction of gravitation will be considerably increased, and the effect will be to accelerate the vibration of the pendulum'. From "Illustrated London News", 1854.