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 36
observer to ascertain with great exactness ASTRONOMY. *9 the time at which a star crosses theequidistant and parallel spider-lines are stretched across thefocus of the telescope, as shown inFig. 21. The observer notes thetime when the star crosses eachspider-line ; and the mean of allof these times…
Astronomy
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