Elements of theoretical and descriptive astronomy, for the use of colleges and academies (1901)
White, Charles J · New York: J. Wiley & sons · leaf 40
Fig. 8. … Fig. 9. the threads of the screw, thus making the number of teeth passedover by the spider threads equal to the number of complete revolutions made by the screw. The central notch is taken as thepoint of reference, and is distinguished by a hole opposite to it.There is a fixed index at i, to which…
Astronomy
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