A treatise on levelling, topography, and higher surveying (1876)
Gillespie, W. M. (William Mitchell), 1816-1868, Staley, Cady, b. 1840, ed · New York, D. Appleton and company · leaf 139
at the formerby reflection. If the brighter objects be to the left or below,hold the instrument upside down. If the angular distance of the object be more than therange of the sextant (about 120°), observe from one of them tosome intermediate object, and thence to the other. A good rest for a… … (191.) Parallax of the Sextant. The angle observed withthe sextant is that made by two lines : one, B I, passing fromthe reflected object to the index-glass, and which is thencereflected to the horizon-glass, and thence to the eye ; and theother, HE, passing from the object directly to the eye; i.…
Surveying
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