The elements of theoretical and descriptive astronomy, for the use of colleges and academies (1872)
White, Charles J. (Charles Joyce), 1839-1917 · Philadelphia, Claxton, Remsen & Haffelfinger · leaf 41
e is a fixed index at i, to which the divisions on the head ofthe screw are referred. When any division of the limb does notcoincide with the central notch, the spider threads are movedfrom the central notch to the division, and the number of revo-lutions and fractional parts of a revolution which… … 86 FIXED POINTS. divisions, then will one revolution of the screw correspond to anarc of 1; and if we further suppose that the head of the screwis divided into 60 equal parts, then each division on the headwill correspond to an arc of 1. In such a case, the completereading of the limb is obtained…
Astronomy
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