Newcomb, Simon, 1835-1909 · New York Harper & brothers · leaf 139
c; that is, an arm moving around this circle would always point towards some part of the equator or the ecliptic, according to the way the instrument was set. The circle in question, being divided into degrees, served the pur- pose of measuring the angular distance of any two bodies in or near the… … Fig. 27.—Armillary sphere, as described by Ptolemy, and used by him and by Hipparchus. The circle El is set in the plane of the ecliptic, the line PP being directed towards its pole. The circle ApMp passes throngh the poles of both the ecliptic and the equator. The inner pair of circles turn on the…
Astronomy
Internet Archive · University of Illinois Urbana-Champaign · Public domain (published before 1931). Free to use for anything.
