EFFECTS OF RADIANT ENERGY ON THE EYE. 



G33 



radiation can enough energy be communicated into interior layers to 

 affect them in a similar manner. To put the thing in another way, it is 

 only relatively inactive rays that through consequent lack of absorp- 

 tion penetrate a medium easily. With sufficient incident intensity, 

 however, enough energy may penetrate the outer layers to produce 

 definite action within them. 



In ordinary transparent media the loss of energy by real absorption 

 in the substance is less than the loss at the surfaces by reflection. 

 This loss depends on the refractive index of the medium with respect 

 to the entering or emerging ray, and for nearly normal incidence the 

 coefficient of reflection, that is the proportion of the ray transmitted 



through a single reflecting surface is K = 



(n - 1) 



— . This coefficient 



is the same for each successive surface of transition, so that for rn 

 surfaces the coefficient of transmission are Km = K™. Thus, if 

 a glass plate has an index of refraction n the light transmitted is K^ 



1.0 I.l 1.2 1.3 1.4 1., 



n 



Figure 1. Transmission of glass surfaces. 



for the two surfaces. In case of an optical system having several 

 lenses, the reflection losses may be severe, particularly if some of the 

 glasses are of high index. Figure 1 shows in curve a the transmission 

 of a single surface for various indices of refraction, and in curve b 

 transmission of a double surface like that presented by a transparent 



