Newcomb, Simon, 1835-1909, Holden, Edward Singleton, 1846-1914, joint author · New York, H. Holt and Company · leaf 113
Fig. 41. the mirrors, since B G and D G are perpendicular to B and A. Tomeasure the altitude of a star (or the sun) at sea, the sextant is heldin the hand, and the telescope is pointed to the sea-horizon, whichappears like a definite line. The index-arm is then moved untilthe reflected image of the… … Fig. 42.—artificial horizon. image of the sea-horizon seen directly. When this occurs the timeis to be noted from a chronometer. If a star is observed, the read-ing of the divided limb gives the altitude directly ; if it is thesun or moon which has been observed, the lower limb of these isbrought…
Astronomy
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