. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. chap, xxiv.] REFRACTION. 309 medium into another of different density, is bent out of its path at the surface of separation of the two media. The deflection is called REFRACTION. Fig. 135 represents a ray of light passing from air into water. If the ray passed perpendicularly into the water, in the direction of the normal NN', its course would be un- affected by the water ; but when it strikes the water obliquely as in- dicated
. The elements of physiological physics: an outline of the elementary facts, principles, and methods of physics; and their applications in physiology. Biophysics. chap, xxiv.] REFRACTION. 309 medium into another of different density, is bent out of its path at the surface of separation of the two media. The deflection is called REFRACTION. Fig. 135 represents a ray of light passing from air into water. If the ray passed perpendicularly into the water, in the direction of the normal NN', its course would be un- affected by the water ; but when it strikes the water obliquely as in- dicated by the arrow, then it does not r Fig. 135.—Refrac- contmue a straight course as HB, but tiou of Light. is bent towards the normal as HC. Or suppose c to be a bright object in the water, and CH to be a ray of light reflected by it, when the ray emerged from the water it would not continue a straight course, but owing to the different density of the air it would be bent away from the normal, and would assume the direction of the line above H. An eye placed at the end of that line would, therefore, receive the rays proceeding from c ; since the eye always refers the luminous object in the direction of the rays which reach it, the eye would seem to see the object c at B, displaced from its true position. Thus, a ray of light passing from one, medium into another of greater density, is refracted towards the normal; and passing from one medium into another of less density, is refracted away from the normal. It is refraction that causes a stick plunged obliquely into water to appear bent, the immersed part being raised nearer to the surface. It is re- fraction also that causes the sun to appear still above the horizon when it has actually sunk below it, the rays from the sun being bent by the atmosphere sur- rounding the earth, the sun is caused to appear higher than it actually is. The mirage seen most commonly in hot climates is also an effect of refrac- tion. Fig. 136 shows how r
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