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 206
nd the silver then re-moved by nitric acid. Silk threads from a cocoon are sometimesused. Spiders threads are, however, the most usual. If a cross-hair is broken, the ring must be taken out by removing two op-posite screws, and inserting a wire with a screw cut on its end,or a stick of suitable… … Fig. 205.
Surveying
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