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 88
to find B B we measure two diameters, 2 E and 2 r, and thedistance apart, h. SIMPLE ANGULAR LEVELLING. Then, B B = 69 B-r &4-] If the oblique distance I be measured instead of A, then E B^ [* +(B-*■)] [J-(B-*•)]. [1.5.] BB = When the spire is very aeute, then this method is inac-curate. , Fig.… … . Take some point, A, and observe zenith distances, 6, 6f\and d. Then: BB h. tang. {d» -6)cos.i(cf/-d + 6} [1.6.] (109.) Levelling by the Horizon of the Sea. From an emi-nence, as B, sight to the sea horizon, and measure 6°= angleABZ. Then: Fig. 87. Z/
Surveying
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