. Elements of astronomy: accompanied with numerous illustrations, a colored representation of the solar, stellar, and nebular spectra, and celestial charts of the northern and the southern hemisphere. ermined. 520. The Earths density has been determined in threeways:— I. By comparing the attractive force of a large metallicball of known size and density, with that of the Earth. II. By finding how much a large mountain will deflecta plumb-line, or draw it toward itself from the perpendic-ular. III. By determining the rate of vibration of the samependulum on the top and at the bottom of a mounta
. Elements of astronomy: accompanied with numerous illustrations, a colored representation of the solar, stellar, and nebular spectra, and celestial charts of the northern and the southern hemisphere. ermined. 520. The Earths density has been determined in threeways:— I. By comparing the attractive force of a large metallicball of known size and density, with that of the Earth. II. By finding how much a large mountain will deflecta plumb-line, or draw it toward itself from the perpendic-ular. III. By determining the rate of vibration of the samependulum on the top and at the bottom of a mountain, or at the bottom of a mineand at the Earths sur-face. C21. The CavendishExperiment.—It willhere suffice to describethe first-mentioned meth-od, adopted by Caven-dish in 1798. The weightof any thing is a measureof the Earths attrac-tion. Cavendish, there- Fig. 110.—The Cavendish Experiment. A B, r. ?, , ?.-, the small leaden balls on the rod G. D E, lore> tooK tw0 Small the suspending wire. F G, the large leaden leaden balls of knownballs on one side of the small ones. HE, , the large leaden balls in a position on the Weight, and fixed them otherside at the ends of a slender (H. be determined ? 519. What must we first find? Why is it not sufficient to. de-termine the Earths bulk ? 520. In what three ways has the Earths density been EARTHS MASS, HOW DETERMINED. 285 wooden rod six feet long, suspended by a fine wire. Whenthe rod was at rest, he placed two large leaden balls oneon either side of the small ones. If the large balls exertedany appreciable attractive influence on the smaller ones,the wire would twist to allow each small ball to approachthe large one near it; and a telescope was arranged tomark the deviation. Cavendish found there was a deviation. This enabledhim to calculate how great it would have been had eachlarge ball been of the size of the Earth. He then had theattraction of the Earth (measured by the weight of the smallballs), and the attraction of
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectastronomy, bookyear18
