. Polarisation of light . the crystal. In every double refract-ing crystal there is at least one, and in many thereare two, directions in which no such separation takesplace. These directions are called optic axes. Therelations between the forms of crystals and their opticaxes, and optical properties arising therefrom, will beexplained later. Of such crystals Iceland spar is the most notableinstance. If we take a block of such spar split intoits natural shape, a rhombohedron, Fig. 9, and forconvenience cut off the blunt angles by planes perpen-dicular to the line joining them a b, it will be s
. Polarisation of light . the crystal. In every double refract-ing crystal there is at least one, and in many thereare two, directions in which no such separation takesplace. These directions are called optic axes. Therelations between the forms of crystals and their opticaxes, and optical properties arising therefrom, will beexplained later. Of such crystals Iceland spar is the most notableinstance. If we take a block of such spar split intoits natural shape, a rhombohedron, Fig. 9, and forconvenience cut off the blunt angles by planes perpen-dicular to the line joining them a b, it will be seenthat a ray of light transmitted perpendicularly to theseplanes, that is, parallel to the line joining the bluntangles, is not divided. In fact, the image either of c i8 POLARIS A TION OF LIGHT. [chap. the aperture of the lantern projected on a screen, or ofan object seen by the eye in the direction in question,appears single, as if passed through a block of direction in question (viz. the line a h itself, and.
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlondo, bookyear1874
