Smith, Hamilton Lanphere, 1819-1903. [from old catalog] · Cleveland, M. C. Younglove and company · leaf 32
S from the object B. To observe this angle, or inclination* wemay use a small graduated circle thus. Let A C D be a circlegraduated into 360°, having a moveable index turning on itscentre, which index is furnished at each end with a sight-hole.First look with the index towards the object B, and… … the index towards S, observe where it makes the circle, say 20°,the difference 10°, is the angular distance of S from B. Theinstruments of Ptolemy were constructed upon this principlethough not so perfect, using shadows, and other contrivances,instead of simply observing through two vanes or sight…
Astronomy · Meteorology · Geology · Paleontology
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