List, C, Hall, T. G. (Thomas Grainger), 1803-1881 · Philadelphia : Thomas Cowperthwait & Co. and Carey & Hart · leaf 54
really describe a curve, on account of the refrac-tion of the atmosphere being different at differentaltitudes. For refraction wholly depends on thedensity of the atmosphere, and the density dimi-nishes as we ascend from the earth. In the figure,let the interior sphere represent the earth, the… … 50 OUTLINES OF ASTRONOMY. density al a is greater than that at b, and that atb greater than that at c. That a star apparently rises before it actuallyreaches the horizon, may be seen by attending tothe figure. Let a be the place of a spectator, a ta plane touching the earth at a, and…
Astronomy
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