﻿668 Mr. G. H. Livens on the Electron 



and thus for the propagation o£ this wave-train to be possible 

 in the medium we must have 



which is the general relation to be satisfied between the 

 electric force and current components. 

 If we put 



n=fi— ik 



and assume that /jl and fc are real the exponential factor is 



-'-tA'-t) 



and thus — is the velocity of the disturbance in the medium, 



and therefore yu, is the ordinary refractive index. The 

 absorption is determined by k, which is therefore called the 

 absorption coefficient. 



8. The equations in the metal. — Now we know J x in terms 

 of E^, and can therefore at once proceed to an examination 

 of the equations as far as they concern the propagation in the 

 metal itself. 



If E x is, as above, of the form ~Ee ip \ «"/ then we know 

 that 



where C is used for the generalized form of the conductivity 

 which we have found to be 



C= — ^ \f *- n | u 3 X (v)e-^du } 



** o 



X(u) having the same significance as before • but 

 and P r = 



AE, 



1-aA 



as before, so that 





