Davies, Charles, 1798-1876 · New York, Cincinnati [etc.] American book company · leaf 96
67we see that the needle at S, instead ofbeing parallel to the needle at P (asindicated by the dotted needle) as itshould be, has been deflected by localattraction (as shown by the full needle),so that its south end is moved 2° to the W., and its north end 2°to the E. of its proper position. Hence… … Fig. 67. 90 ELEMENTS OF SURVEYING. [book III. If 110 buck-sight and its fore-sight agree, then take the meanof the back-sight and fore-sight which differ least; or seek someground at a distance, free from local attraction, and then workinto the plot to be surveyed, correcting each fore-sight onthe…
Surveying
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