Lockyer, Norman, Sir, 1836-1920, Seabroke, G. M. (George Mitchell), 1848-1918 · London, Macmillan and co. · leaf 237
ding edge of the pointer cuts the diagonalline at three-fourths of its length, as shown by the thirdcircle ; so the reading in this case is seven and three-quarters ; but that is, after all, a very rough method,although it was all the astronomer had to depend uponin some important observations. The… … FiG. 102.—The Vernier. ciple in this way. Suppose for instance we want tosubdivide the divisions marked on the arc of a circle,Fig. 102 a h, and say we wish to divide them intotenths, what we have to do is this—First, take a lengthequal to nine of these divisions on a piece of metal, c,called the…
Astronomy · Telescopes
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