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 515
a horse-shoe nail, with a hole through the head large enough to take theline of a plumb-bob or plummet-lamp. The spud is driven in acrack in the roof, or in a wooden plug which is driven in a holethat has been previously drilled. The objections to this methodare, the length of time it takes to get… … the plugs out of sight with the ends of their drills. Probably, assatisfactory a way as any to mark the point is to drill a shallow hole, about one eighth of an inchin diameter, in the center of apainted -}-, or a circle about sixinches in diameter. Fig. 559shows a very convenient devicefor marking…
Surveying
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