The outlines of physics: an elementary text-book (1897)
Nichols, E. L. (Edward Leamington), 1854-1937 · New York, The Macmillan Company; London, Macmillan & Co., Ltd. · leaf 448
Fig.39a !ommonly a fixed cross hair to mark;he middle of the field of view, andsometimes the moving hair is sup-planted by two crossing each other atan oblique angle. In the latter =F^ Fig. 401. Fig. 400. case the appearance of the field is that represented in Fig. 400.This is a more elaborate…
Physics
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