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64 LIGHT AND WATER obliguely (at an angle of 80"), a much larger portion (about one-third) escapes at the surface and is reflected along Oe.! Figs. 25 (III) and (IV) are similar to (1) and (II) respectively, the light now travelling in the direction of the arrows from a source below the surface, and here in the same way a much larger proportion of the beam CO passes out of the water than of the more oblique beam ¢QO, which is nearly all reflected down again to a. Fig. 25 (III). Fig. 25 (IV). If Figs. 25 (1) and (III) were placed one on the top of the other, the point O on the point O, and the line MN on the line MN, then the lines OE, OD, in each diagram would also coincide. A combination of the two diagrams would therefore represent the light coming to the eye, if placed at E and directed . The following figures are taken from " Light,” by Professor Tyndall. At perpendicular incidence, (ze, at 0") water reflects 18 rays per 1,000 : at 40. ,9 99 22 99 9 3? at 60 )) )) 65 )) 9) )) at 80 99 99 333 ” ,) whilst at 891 9 ‘3 721 ,, ) 3
