and Electromagnetic Theory. 315 



The tangential stress-component is not balanced until the 

 motional terms are taken into account. In the above they 



are u-Pj, ic~P 2 on the left, and — ^ on the right hand. For 



the other component Q takes the place of P. 



§ 17. The modification of the equations to include current 

 Ox ig ie) treated as a line-discontinuity is simple. In the 

 main we are concerned with the case of free aether, but tor 

 the present K and M are retained, and the work is written for 

 the non-aberrational form, i. e., translation is relative to the 

 dielectric. We have then, for the moving standpoint, 



v dX . ^ T (dy' d/3'\ „dct ^{dY' dZ'\\ 



X'=X + M(i>y-w/S)/V, a ' = a + K(wY-vZ)/YJ 



with P = KA and t+#=0. 



dx dt dx 



In terms of letters without dash, we have, if u v w are constant, 



, T>'_d d d d 



Dt dt dx dy dz 1 



From the standpoint of the dielectric itself, these equations 

 are 



TrdX t , . Tr Afy d/3\ ^da ^ T /dY dZ\ fKKX 

 K^ +pu + tz =Y{^-£), M dT =V(^- rf7 ).(55, 



The energy equation attaching to (53) contains terms in 

 i £ ... in addition to those found in §11; and we may also 

 write those which result from supposing u v to to depend on t. 

 Thus 



J+SPj+^ x X / + VS^(YV-Z'/S')=0, (56) 



with a term for Joule's effect, and one combining the 

 momentum of radiation with acceleration in translation. 



But if we set out from (55), i. e. take the standpoint of 

 the dielectric, and use E, we get with multipliers X ... a, 



^ + P tuX+tiJL = -VS~(Yy-Z8). 



