330 .MACiNKTISM 



We may represent the general nature of the change in 

 l/^or M 2 by Fig. 244. 



This theory holds good in the clcctro-magm tit thcorv it we 

 suppose that the medium consists of mitral bodies round uhirh 

 electrons or small charged bodies are revolving, each with a pi-rind 

 or periods of its own. \Ve make the iiMinl supposition that the 



t 



I 



K+/3/N 

 K 



**7t N 



charge on each electron has the same n< iluc. NVe repi 



it numerically by f and the ma>s of the clc< tum by m. 



Now let a circularlx polarised beam of fr n travel 



through the medium. We suppose that it makes t: 

 whirl round the centres of their natural orbit- 

 frequency n, instead of the natural fiequencx N. the a\e di-- 

 turbance" calling into play a force which, added to m.in^N 1 ^ the 

 natural force of the s\stem, accounts lor the i 



When a field II is put on, let tix suppo-i 



coincides with the dirt ct ion in which > tiaxrlling. Il 



the distance of the electron < tiom it is %-jriid, 



and as it is moving transxciscly to t II idial : . 



to II, equal to girfi</Hr, will be called into )1.\. The 

 electron moving clockwise is equixah nt to a |>oit: 

 lating counter-ilockwisi-. 11 ix inwaids on an 



electron moving clockx\i>e and outw.-,- 



clockwise. If m \^ the i ion, th- n at 



distance d is 2ir</Hr/w. The total aco i due to the 



internal force and to this magnetic tone is 



and this is the natural acceleration wh< n the field ix on. 



Putting (1) in the form wV, we -ee that there are now two 

 different natural frequencies, gixui by w/2x, where <u has the 

 value 



