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 145
he sun is the object observed, to determinewhether it is his upper or lower limb whose altitude has beenobserved, proceed thus: Having brought two limbs to touch, push the index-armfrom you. If one image passes over the other, so that theother two limbs come together, then you had the lower limbat… … (201.) To observe very small altitudes and depressions withthe artificial horizon: THE PKACTICE. 127 Stretch a string over the artificial horizon. Place yourhead so that you see the string cover its image in the mercury.Then the eye and string determine a vertical plane. Then observe, looking at…
Surveying
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