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 76
etched across the opening on theother side, or a mark on the glass.The box is held in the hand overthe spot where the perpendicular isdesired (a plumb-line in the handwill give perfect accuracy), and theobserver applies his eye to the slitA, looking through the upper orunsilvered part of the glass,… … * The French call the narrow opening ceillelon, and the wide one croisee. 62 LAND-SURVEYING. parts of the glass, by reflection through the opening D, till hisrod, at E, is seen to coincide with, or to be exactly under, the ob-ject B. Then is the line DE at right angles to the line A B, bythe…
Surveying
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