. Light, a textbook for students who have had one year of physics. away. The substitution of water for air, as the mediumin contact with the cornea, alters the refraction so that it isimpossible, at least without extreme eye-strain, to focus uponthe retina. Therefore human vision with the eyes in contactwith water is very much blurred and indistinct. 26. Deviation through a prism.—We shall now considerthe deviation of light by a prism (figure 27) ; and since, inthe actual use of prisms for the production of spectra, thelight waves are practically always first made plane by the useof a lens, we
. Light, a textbook for students who have had one year of physics. away. The substitution of water for air, as the mediumin contact with the cornea, alters the refraction so that it isimpossible, at least without extreme eye-strain, to focus uponthe retina. Therefore human vision with the eyes in contactwith water is very much blurred and indistinct. 26. Deviation through a prism.—We shall now considerthe deviation of light by a prism (figure 27) ; and since, inthe actual use of prisms for the production of spectra, thelight waves are practically always first made plane by the useof a lens, we shall take only the case of plane waves. Ateach surface of the prism, not only refraction occurs, but alsoreflection; but in this discussion we shall ignore the reflectedlight. For the sake of symmetry,Ave call ij the angle of incidenceat the first surface, i\ the corre-sponding angle of refraction, r3the angle of incidence at the sec-ond surface and i2 the correspond-ing angle of refraction; so thati, and i2 are angles in air, r, andr. angles in glass. Then. sin. l n = sin. r, sm. i2sin. r, / glass Figure 27 where n is the index ofwith respect to air. The drawingshows a series of wavefronts sup-posed to be just one wavelength apart (for instance the lines of the crests) both in theair and in the glass, though of course the actual length of the 60 LIGHT Light waves, as compared to the dimensions of a practicableprism, is enormously exaggerated in the figure. It will benoticed that the wavelength is shorter in glass than in this must be so, for the following reasons: The period,or time of one vibration, must be the same in glass as in air,for only so many waves can in a given time leave the surfacetoward the glass side as come up to it on the air side. Also,since a train of waves advances the distance of one wavelengthduring the time of one vibration, . ., wavelength velocitv — :—-— period Therefore, since the period is the same in the two media, wavelength i
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectlight, bookyear1921
