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COLOURS IN STILL WATER 63 where it enters the water. The angle of refraction, as explained in the note above, bears a certain definite relation to the angle of incidence. That which at present concerns us is, however, not the relation of these angles, but the amount of light that passes Írom air into water compared with the amount that is reflected at the surface; and again, the amount that passes out of water from a point beneath the surface compared with the amount that is reflected down Fig. 25 (1). Fig. 25 (II). again into the water. We shall find that the more obliquely the ray falls on the surface, the more of it will be reflected and therefore the less refracted, and vice versd, the more perpendicularly it falls on the surface, the more will enter the water and the less be reflected. This principle is roughly illustrated in Fig. 25 by the relative thicknesses of the lines representing the rays of light. For example, in Fig. 25 (1) almost the whole of the ray AO (inclined at an angle of 40°) is refracted along OD, only a very small fraction of the light (about one-fiftieth) being reflected, whereas in (II), where the ray @O strikes the surface very
