Wentworth, G. A. (George Albert), 1835-1906 · Boston, Ginn · leaf 88
nstrument isequally distant from A and B, or nearly so, the curvature andthe refraction on the two sides of the instrument balance, andno correction for curvature or refraction is necessary. Several Settings of Instrument. When both places are notvisible from the same place, or when the difference… … Fig. 54 Find A A and BB, as in the preceding case, and record theformer as a backsight and the latter as a foresight. Selectanother intermediate station C, and in like manner find thebacksight BB and the foresight CC; and so continue untilthe place D is reached. The difference between the sum, of…
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