135 

 rot H = - b , 



rot E = H . 



c 



(H magnetic force, c velocity of iiglit in tlie aether). 



We sliall, in the usual way, represent tlie vibrations of the system 

 by means of complex expressions, so that, if n is the frequency, 

 all variable quantities contain the factor 



Introducing 



». =!/'-• 



y^ m 



the frequency of the free vibrations, we tind from (1) and (2) 



P=S r- E . 



»«(n„"— n') -j- hig 



A beam of light travelling in the direction of the axis of ,v, may 

 be represented by expressions for E, DandH, containing the factor 



where (ft) may be called the "complex index of refraction." Fortius 

 quantity we find from the above equations 



^ 2. !f novv we put 



ich 



(m) = M (4) 



n 



(I will be the real index of refraction and h the index of absorption. 

 The meaning of the latter is, that the intensity of a beam of light 

 travelling over a distance ö, is diminished in the ratio of 1 to 



t'-2W (5) 



By means of (3) jt and h may be determined for each frequency 

 of the light. 



If the values of ?2„ for the diiferent groups of electrons are suffi- 

 ciently different from each other, there will be a certain number of 

 separate maxima of absorption. In this case we may treat the phenomena 

 belonging to each of these maxima with sufïicient approximation by 

 supposing only one group of corpuscles to be present. 



Thus (3) becomes 



10* 



