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 487
d E betwo mirrors, perpen-dicular to the plane ofthe paper. Let a rayof light from the ob-ject A be reflectedfrom the mirrors Dand E to the eye at C,and B be the other object, looked at directly. Erect perpendicu-lars to the mirrors, and prolong them until they meet at F. Pro-long the line A D… … V-F THE SEXTANT. 473 then we have : DCE=ADE-DEC DCE = 2(GDE-DEF) DCE = 2DFE. 701. Description of the Sextant (Fig. 520). The frame is usuallyof brass, constructed so as to combine strength with lightness. The Fig. 520.
Surveying
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