A text-book of general astronomy : for colleges and scientific schools (1888)
Young, Charles A. (Charles Augustus), 1834-1908 · Boston ; London : Ginn & Company · leaf 105
ined. Erect upon a level plain threerods in line, a mile apart,and cut off their tops atthe same level, carefullydetermined with a sur-veyors levelling instru-ment. It will then befound that the line AC,Fig. 44, joining the ex-tremities of the two terminal rods, passes about eight inches below B,… … Fig. 44.— Curvature of the Earths Surface. BD 2 BD whence Now BA is one mile, and BD— § of a foot, or 7J2Jj of a mile. I2Hence 2R — ——, or 7920 miles : a very fair approximation. 7920 On account of refraction, however, the result cannot be made exact byany care in observation. The line of sight,…
Astronomy
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