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 120
needle is perfectlystraight, and whether the pivot is exactly in the center. In Figs.137 and 138 both of these are represented as being excessively inerror. First, to examine if the needle be straight. Fix the pivottemporarily so that the ends of the needle may cut opposite de-grees—i. e., degrees… … as is shown by Fig. 138, in which the former position of the needleis indicated by a dotted line.* Now bend the needle, as in Fig.139, till it cuts divisions midway betwen those cut by it in itspresent and in its former position. This makes it certain that theneedle is straight, or that its two…
Surveying
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