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 146
ig. 160, the supplement of the zenith distance. Otherwise. Fix behind the horizon-glass a piece of whitepaper with a small hole in it, and with a black line on it per-pendicular to the plane of the arc. Then look into the mercury, so as to see in it the imageof the line. Your line of sight is then… … horizontal line. Mark two points equally distant from theeye. Measure, by the preceding method, the angles j3 and j3,which C A and C B make with the vertical CD. Then willhalf the difference of these angles equal the angle which theslope makes with the horizon. • Demonstration. Continue the…
Surveying
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