Lockyer, Norman, Sir, 1836-1920, Seabroke, G. M. (George Mitchell), 1848-1918 · London, Macmillan and co. · leaf 251
rom any object, that object appears doubled. There is,however, a certain direction in the crystal, along which,if the light travel, it is not divided into two rays, andthis direction is that of the optic axis of the crystal,A A, Fig. 110; if therefore two prisms of this sparare made so that in one… … Fig. 110.—Crystals of Iceland Spar showing, A a, the optic axis. the first one without being split up, since it passesparallel to the axis, but on reaching the second one it isdivided into two rays, one of which proceeds on in theoriginal course, since the two prisms counteract eachother for this…
Astronomy · Telescopes
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