The theory and practice of surveying. Designed for the use of surveyors and engineers generally, but especially for the use of students in engineering (1886)
Johnson, J. B. (John Butler), 1850-1902 · New York, J. Wiley & sons · leaf 577
5 2100 090 3100 .197 4100 •345 5100 533 9 46.275 1200 .030 2200 099 3200 .210 4200 .362 5200 554 10 57-130 399. Formulae for an observed Angle of Depression toa Sea Horizon.—In Fig. 148 let A be the point of observa-tion and 6* the point on the sea-level surface where the tangentfrom A falls. Then… … then and or 2 ^ If the observed angle of de-pression h^ h^= C — mC^ C = h I — ifC 2 \\ — m (13) H^A- 2\i ~ in.where h is expressed in seconds of arc. tan \, (14) Log — tan \ r= 6.39032 for distances in feet.400. To find the Value of m we have whence or or Z = 90° — k-\- mC, Z^Z - 180°+ (7= \Zo° - h…
Surveying
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