. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. Chap, xxx.] POLARISATION OF LIGHT. 401 at right angles to the former it is extinguished. The ray, therefore, which exhibits these phenomena, when examined by a Nicol's prism, has peculiar characters. It is said to be plane polarised. Polarisation of light.—Ordinary light, ac- cording to the wave theory, is due to vibrations occurring transversely to the direction of propaga- tion of the wave, but the vibrations take place in all plan
. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. Chap, xxx.] POLARISATION OF LIGHT. 401 at right angles to the former it is extinguished. The ray, therefore, which exhibits these phenomena, when examined by a Nicol's prism, has peculiar characters. It is said to be plane polarised. Polarisation of light.—Ordinary light, ac- cording to the wave theory, is due to vibrations occurring transversely to the direction of propaga- tion of the wave, but the vibrations take place in all planes across the direction of the wave. Light is said to be plane polarised when the vibrations take place all in one plane. To put it in another way. The par- ticles of ether, whose vibrations produce light, all move in directions transverse to the direction of propagation, but in their vibrations they may de- scribe figures of various forms, straight lines, circles, etc. When light is polarised, however, the particles of ether are all made to vibrate in the same direction, in straight lines in the same plane. In. Fig. 181 let BA represent a ray of ordinary light. The ^ velocity of a body along the line BA may be decomposed into two velocities at right angles, one, namely, in the direction BY, the velocity in that , . , . -, V i j —Decoin- direction being represented by BA , and position of a the other in the direction BX, the ^o^^ht velocity being represented by BB'. Angles to one Similarly the velocity of a body along BC may be considered as compounded of a velocity BC' and BD, BC being, in short, the resultant of the two velocities. So, letting BA represent a ray of ordinary light, it may be considered as compounded of vibrations occurring in the direction By and , with different velocities represented by BA' and BB'. BA' and BB' will represent polarised rays. An ordinary ray of light may then be decomposed into two rays polarised in planes at right angles
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