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 116
line from thoeye of the observer passes above the former, and in the same verti-cal plane, the angle is called an angle of elevation. When the latter line passes below the horizontal line,and in the same vertical plane, the angle is called an angleof depression. When the two lines which form an… … THE COMPASS. 168. The Needle. The most essential part of the compass isthe magnetic needle. It is a slender bar of steel, usually five orsix inches long, strongly magnetized, and balanced on a pivot, sothat it may turn freely, and thus be enabled to continue pointingin the same direction (that of…
Surveying
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