Note:  Do not rely on this information. It is very old.

Cavendish Experiment

Cavendish Experiment, a method devised by Michell, and improved by Henry Cavendish, to determine the constant of gravitation; that is, the force with which unit mass attracts unit mass when the two are placed at unit distance apart. A knowledge of this enables us to calculate the mass of the earth. Two spheres of equal mass are suspended from the ends of a thin horizontal rod, supported at its centre by a fine vertical wire. Two larger spheres are placed so as to turn the horizontal rod by attracting the smaller masses, and the time of oscillation of the rod is observed. This and a few data of the different positions of the rod are sufficient to determine the required constant. Baily's experiments gave it the value 6.48 x 10-8 with the ordinary absolute units; the mass of the earth is then 6.14 x 1027 grammes, or about 5 x 1024 tons, and its mean density 5.67 as compared with water. The Cavendish experiment is being repeated with much greater accuracy and on a much smaller scale by Professor Boys.