Fig. 2 will evidently be much flattened, so that we can safely assume the portion of itthat we are considering to be plane. Imagine such a plane wave-front,R R R, (Fig. 3) striking a plane surface of glass obliquely. Then the lighttraveling along the ray P R will enter the glass sooner than that… … Fig. 3 retarded or commence to travel slower, before that along P R does. Duringthe time the light has traveled from R to S in air, it has only traveled fromR to S in glass. Now experiment has shown, and mathematical analysis has demon-strated, that a ray falling thus obliquely on a glass surface…
Lenses · Eyeglasses
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