Wentworth, G. A. (George Albert), 1835-1906 · Boston, Ginn & company · leaf 232
t the rodman now record the height AAof the target. In like manner find BB. The difference be-tween A A1 and BB will be the difference of level required.If the instrument be equally distant from A and B, or nearlyso, no correction for curvature will be necessary. If the instrument be set up at one… … THE Y LEVEL. LEVELLING FOR SECTION. 61 To find the difference of level of two places, one of which cannotbe seen from the other, and both invisible from the same place; or,when the two places differ considerably in level, Let A and D (Fig. 44) represent the two places. Place thelevel midway between…
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