CH. IX] INDEX OF REFRACTION AND VELOCITY 



277 



I have followed the more common definition which makes it the greatest angle 

 ?t which a ray can emerge into the rarer medium; the emerging angle will then be 

 90 and its sine i.ooo. 



450. Table of refractive indices. (From Chamot). 

 (Temperature 20 to 22 C.) 



451. The sine law and the velocity of light in different media. 

 In the ether of space all wave lengths of light move with equal velocity, 

 but on the earth the velocity depends on the wave length. While all 

 wave lengths are retarded by shortening the waves, the shorter the 

 original wave the greater the retardation. As the refraction of the 

 light is one of the phenomena of this retardation it follows that 

 the shorter the wave the greater the bending. This is shown by the 

 action of the prism (fig. 145, 2), in which the blue is more deviated 

 than the red. 



The retardation of any given wave length (i.e. the relative shorten- 

 ing of the waves) follows the sine law in passing from one transparent 

 substance to another. For example, in passing from the ether to 



water the speed in water would be represented by: - - or 1.334 for 



sin r 



