JAMIN ON METALLIC REFLEXION. 



Mirror-metal. — Square root of the intensities of light reflected 

 perpendicularly to the plane of incidence. 



In the fourth column of the preceding tables are given the 

 numbers as calculated, between which and those furnished by 

 experiment there is a satisfactory agreement : these numbers are 

 given by formulee due to M. Cauchy. This geometer, guided by 

 the experiments of Sir David Brewster, has treated the problem 

 of metallic reflexion theoretically, and we shall soon see that he 

 has completely solved it. As his labours on this subject have not 

 been published as a whole, we think fit to give here an abstract 

 of the theoretical principles on which they are founded, and to 

 state the formulae at which he has arrived. 



When light passes from vacant space into a homogeneous 

 body, there exists between the lengths of the incident and re- 

 fracted waves, a ratio which has been named the index of refrac- 

 tion, and which is constant when the body is homogeneous and 

 not crystallized. If this body is transparent, the index of refrac- 



tion is its sole characteristic, and the knowledge of this constant 

 is sufficient to calculate in every case the action exerted by the 



