. The principles of physics. PATH dislandc Fig. 305. wh^n it has two such axes. A plane parallel to this axis andperpendicular to one of the rhombic faces of the crystal iscalled a principal section. The two rays travel with unequalspeeds in the crystal in all directions except in the directionof the optic axis of the crystal. The property of double refraction may be imparted per-manently or transiently to certain substances which do notnaturally possess it. Glass may be given this power byheating different parts unequally, and also by compressionand 404 ETHER DYNAMICS. 364. Nicol pr
. The principles of physics. PATH dislandc Fig. 305. wh^n it has two such axes. A plane parallel to this axis andperpendicular to one of the rhombic faces of the crystal iscalled a principal section. The two rays travel with unequalspeeds in the crystal in all directions except in the directionof the optic axis of the crystal. The property of double refraction may be imparted per-manently or transiently to certain substances which do notnaturally possess it. Glass may be given this power byheating different parts unequally, and also by compressionand 404 ETHER DYNAMICS. 364. Nicol prism. For certain purposes, such as are indicated in § 371, it is best toallow only one of the two rays to leave the prism (that, namely, inthe direction of the incidejit light), and to elimi-nate the other. The Nicol prism consists of acrystal of Iceland spar divided diagonally, asa h (Fig. 306), the two surfaces being cementedtogether with Canada balsam. All the facesof the prism are painted black except the twoend faces. The extraordinary ray, fallingupon the transparent balsam at an angle lessthan the critical angle, passes through it, butthe more refracted (or ordinary) ray meets thebalsam at an angle greater than the criticalangle,^ and is therefore totally reflected,thrown to one side of the prism, and absorbedby the black paint. 365. Polarization of light hy double refraction. — On exami-nation of the two rays resulting from splitting a single rayby double refraction, it is found that each is unlike a ray ofcommon light, that each has propert
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectphysics, bookyear1895
