. A treatise on diseases of the eye . e of the lightpasses through it. A portion of the incident wave is reflected, and theremainder is absorbed. PRISMS 89 Law of Refraction.—Wlien liglit, having passed through one medium,enters a second medium whose density is greater than that of thefirst, any ray which meets the separating surface ohlicjuely is refractedor bent toicard the normal to this surface, hut the ray which meets tliesurface perpendicularly undergoes no change of direction (Fig. 53).When the second medium is rarer than the first, the opposite conditionprevails; that is, the ol)li(jue
. A treatise on diseases of the eye . e of the lightpasses through it. A portion of the incident wave is reflected, and theremainder is absorbed. PRISMS 89 Law of Refraction.—Wlien liglit, having passed through one medium,enters a second medium whose density is greater than that of thefirst, any ray which meets the separating surface ohlicjuely is refractedor bent toicard the normal to this surface, hut the ray which meets tliesurface perpendicularly undergoes no change of direction (Fig. 53).When the second medium is rarer than the first, the opposite conditionprevails; that is, the ol)li(jue rays are refracted awai/ from the is a consecjuence of the wave motion of light, ihe degree ofrefraction which a ray undeigoes depends upon the obli(|uity of theray, being greater as the obliquity is greater, and upon the difference indensity of the two media. The relative density—or, to be more exact, the relative power of thesubstances to retard the progress of light—constitutes the rrfrartiveindex. Fig. 53. Illustrating the law of refraction. The angle formed by the incident ray with the normal to the surfaceis called the angle of incidence (i, Fig. 53). The angle formed by therefracted ray with the normal to the surface, is called the amjle of refrac-tion {r, Fig. 53). The index of refraction is determined by dividing the sine of theangle of incidence by the sine of the angle of refraction. The index is usuallv expressed by the letter n. Therefore, ?? = . ^ sm. ?• Passage of Light through a Body with Parallel Plane Surfaces.— When liiiht passes througli a medium bounded by parallel j)lane surfaces,and reenters the original medium, the deviation of any ray wiiich occursat the first surface is exactly neutralized by that wliich occurs at thesecond surface, for the angle of incidence at the first surface is e(|ual tothe angle of refraction at the second surface (Fig. 54). Hence the finaldirecti(jn of any ray wiiich j)asses through such a body is th
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecteyediseases, bookyear
