Astronomy for the use of schools and academies (1882)
Gillet, J. A. (Joseph Anthony), 1837-1908, Rolfe, W. J. (William James), 1827-1910 · New York : Potter, Ainsworth, & Co. · leaf 32
of the divisions on the circles, a device called avernier is often employed. It consists of a short, graduatedarc, attached to the end of an arm c (Fig. 17), which iscarried by the axis, and turns with the telescope. This arcis of the length of nine divisions on the circle, and it isdivided into… … Fig. 17. of a division to the leftoi 9. etc. Hence, when1 coincides with 7. owill be at 6-^ : when 2coincides with 8. o willbe at 6T-0- : when 3 coincides with 9. o will be at 6^. etc. To ascertain the reading of the circle by means of thevernier, we first notice the zero line. If it exactly…
Astronomy
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