Smith, Hamilton Lanphere, 1819-1903. [from old catalog] · Cleveland, M. C. Younglove and company · leaf 125
his twilight fades when the sun has sunkbelow the horizon a certain distance ; thus, let C be the positionof a spectator upon the earth, encompassed with its atmosphere,and SAB the lowest ray of the sun after sunset, B C being thehorizon, The suns rays would now illluminate the portion ofatmosphere… … or one-fortieth of the whole circle. The angle B C O is evident-ly a right angle, or 90°, consequently, from the well known prin-ciple that the square of the longest side of any right angled tri-angle, as B O C, is equal to the sum of the squares of the othertwo sides; the square of B O, is equal…
Astronomy · Meteorology · Geology · Paleontology
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