. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. TOTAL REFLECTION 41. Fig. 12. Total reflection in diamond when surrounded by air. which are incident at an is very small the incident ray will make a large angle with the normal before total reflection takes place. In diamond, which has a very high refractive index relative to air, the angle of total reflection is small, namely 24° 24', which is re
. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. TOTAL REFLECTION 41. Fig. 12. Total reflection in diamond when surrounded by air. which are incident at an is very small the incident ray will make a large angle with the normal before total reflection takes place. In diamond, which has a very high refractive index relative to air, the angle of total reflection is small, namely 24° 24', which is represented by the angle A-fiD in Fig. 12. A ray of light inclined to the normal at an angle slightly less than A^CD will be refracted and pass out into air in the direction CB^ while one inclined at a slightly greater angle will be totally reflected in the stone in the direction CB\. The ray A^C, making a still larger angle with the normal, will be totally reflected along CB^, while the ray Afi will pass out of the stone along CB^, not undergoing total reflection. If the optically denser body is, instead of diamond, glass, having, say, a refractive index of 1-538, then the angle of total reflection will no longer be 24° 24' but 40° 30', the body, as before, being surrounded by air. In this case, only those rays angle greater than 40° 30' will be totally reflected. Since the angle of total reflection increases when the difference between the refractive indices of the two media decreases, it follows that the angle of total reflection will be greater if the stone is surrounded by water instead of air. The angle of total reflection for a diamond placed in methylene iodide, the refractive index of which is 1-75, will be 46° 19', the angle A^CD in Fig. 13. Some of the rays, the obliquity of which causes them to be totally reflected when the diamond is surrounded by air, will be refracted when the surrounding medium is methylene iodide ; thus fewer rays will in this case be totall
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