. 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. Fig. 34.—Hokizoxs of the Same Place, at Diffekent Heights. the only figure which, looked at from any external point,is bounded by a circle; and as the horizons of all placesare circular, the Earth is a sphere, or nearly so. 161. What is the Sensible Horizon ? What proof of the Earths roundness does 84 THE *°utm pourFig. 35.—Poles and Equator. 162. Poles, etc.—The Earth isnot only round, b
. 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. Fig. 34.—Hokizoxs of the Same Place, at Diffekent Heights. the only figure which, looked at from any external point,is bounded by a circle; and as the horizons of all placesare circular, the Earth is a sphere, or nearly so. 161. What is the Sensible Horizon ? What proof of the Earths roundness does 84 THE *°utm pourFig. 35.—Poles and Equator. 162. Poles, etc.—The Earth isnot only round, but it rotates orturns on an axis, as a top doeswhen it is spinning; and the namesof JSTorth Pole and South Pole aregiven to those points where theaxis would come to the surface ifit were a great iron rod instead ofa mathematical line. Half-way be-tween these two poles, there is animaginary line running round theEarth, called the Equator or Equinoctial Line. The line through the Earths centre from pole to pole,is called the Polar Diameter ; the line through the Earthscentre from any point of the equator to the opposite point,is called the Equatorial Diameter • and one of these, aswe shall see, is longer than the other. 163. Proofs of the Earths Rotation.—We owe to theingenuity of the French philosopher, Foucault, two ex-periments which render the Earths rotation visible to theeye. For, although it is made evident by the apparentmotion of the heavenly bodies and the consequent suc-cession of day
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectastronomy, bookyear18
