A treatise on surveying, comprising the theory and the practice ; (1887)
Gillespie, W. M. (William Mitchell), 1816-1868, Staley, Cady, 1840- [from old catalog] ed · New York, D. Appleton and company · leaf 373
Fig. 372. … 525. Troughtons Level. In this the bubble-tube is perma-nently fastened in the top of the telescope-tube. It is adjusted bythe peg method, or some similar one, the cross-hair being movedup or down until the observation gives the true difference of heightof the pegs when the bubble is in the center.…
Surveying
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