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Show Old Experiment Measures Weight of the Earth The measuring of the mass or weight of the earth is a familiar astronomical problem. Other bodies bod-ies are weighed by measuring the attraction of the earth upon them; the same end is accomplished in the case of the earth, by comparing the attraction which this globe exerts upon some body on its surface with the attraction exerted upon the same body by a known mass at a known distance. There have been several methods tried to accomplish this, the simplest of which is that of observing the deviation de-viation from the vertical of a plumb-line plumb-line near an isolated mountain. The volume of the mountain must first be found, of course, by accurate survey, and its density calculated from the geological structure and density of its component rocks. But this plan, though simple, is not nearly near-ly as accurate in result as that of computation by means of the torsion tor-sion balance. This method is known to astronomers as the "Cavendish experiment," from the scientist who first applied it in 1789. Cavendish's methods consists of measuring very accurately the attraction at-traction exerted by two large j spheres of metal, on two much smaller metal balls. Two globes of lead are attached to the extremities extremi-ties of a large horizontal bar, movable, mov-able, horizontally, upon a center. Above this center a light horizontal rod, having on its ends two very small balls of lead, is supported by a fine wire. When the rod bearing the small balls is in equilibrium, the ball having the globes of lead is moved until these globes are brought nearly in contact with the small balls. The force of their attraction then tends to draw the small rod from its position of equilibrium, and the amount of torsion thus produced is measured carefully. This experiment is repeated several sev-eral times, and the average of its results re-sults takpn, so as to be as nearly accurate. s possible. It is plain that the attraction of the large globes on the small ball is to the attraction of the earth upon the small balls i. e., their weight as the mass of the large balls is to the mass of the earth. The result of these experiments has given the weight of the earth approximately approx-imately as 6,000,000,000,000,000,000,-000 6,000,000,000,000,000,000,-000 tODS. |