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 357
ly on a level, and mark where the plumb-line comes to on the bottom of the rod. Turn the instrument around and sight again, and note the place of the plumb-line. The midway point is the right one. 342 LEVELING. A modification of the last form is to fasten a common carpen-ters square in a slit in… … 501. Reflecting Levels. In these, theperpendicular to the direction of gravityis not an actual line, but an imaginaryreflected line. It depends on the optical principle that a ray of light whichmeets a reflecting plane at right angles is reflected back in thesame line. When the eye sees itself in a…
Surveying
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