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 36
at X.They are moved by means of the screws shownat B B. A A are screws used for centring theeye-piece. C C are screws used for centringthe object-glass. At D D are rings, or collars,of exactly the same diameter, turned very truly,by which the telescope revolves in the wyes. The telescope shown in… … (29.) The Cross-hairs. These are made of very fine pla-tinum wire or of spider-threads. They are attached to a short, thick tube, placedwithin the telescope-tube, through which passloosely four screws whosethreads enter and takehold of the cross-hairring, as shown in Fig.21. In some instruments,one…
Surveying
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