Elements of natural philosophy (Volume 2-3) . the second, or denser medium in reference to the first, Equationsapplicable to tbodeviations; sin <p =sin <p == m sin <p m sm <p n 1 (7) it Multiplying these Equations together, there will result Result ofoperations; tt m m = — r^\ m (T) Rule. Example; Result That is to say, to find the index of refraction in the caseof a ray passing from any one medium to another, dividethe index of the second by that of the first referred to avacuum. The index thus obtained is called the relativeindex. Example. What is the relative index of air and cr
Elements of natural philosophy (Volume 2-3) . the second, or denser medium in reference to the first, Equationsapplicable to tbodeviations; sin <p =sin <p == m sin <p m sm <p n 1 (7) it Multiplying these Equations together, there will result Result ofoperations; tt m m = — r^\ m (T) Rule. Example; Result That is to say, to find the index of refraction in the caseof a ray passing from any one medium to another, dividethe index of the second by that of the first referred to avacuum. The index thus obtained is called the relativeindex. Example. What is the relative index of air and crownglass, the light entering the latter from the former? Thetabular index of crowm glass is 1,52, and that of air is1,0003, whence 1,5200 At^ = 1,52. 1,0003 ELEMENTS OF OPTICS. 179 § 21. If a ray pass from amedium to another more dense,the index m will be greaterthan unity, and from equation(7), we shall haveisin sin <p; and if sin <p be taken a maxi-mum, or the angle of incidencebe 90°, equation (7) will give, Fig. Light passingfrom rarer todenser medium; Angle ofincidence taken90°; J- * A ft — = em m (8) from which results a maximum limit to the angle of Maximum limitrefraction. If m be taken equal to 1,52 for the atmos-to angle of x refraction; phere and crown glass, sin 0 = 0,657, or 0 = 41° 5 30, nearly; Example, atmosphere andcrown glass; for air and water, m = 1?33, and Atmosphere andwater; 0 = 48° 15; that is to say, the greatest angle of refraction which canexist when light passes from air into crown glass, is 41°5 30; and from air into water, 48° 15. If the ray pass from a medium to another less dense, 180 NATURAL PHILOSOPHY Light passing m will be less than unity,from denser to an(j eqUal to the reciprocal rarer medium; _ of its former value ; Equa-tion (7) will then give sin sin <p ; Angle of taking the maximum value refraction taken . .. 1 90°; for sin <p = 1, we shall ob- tain from the same Equation, Fig. 10.
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