6l8 GENERAL THEORIES. 



if we take these directions as axes of co-ordinates, and call K x , 

 K 2 , and K 3 , the three principal values of the specific inductive 

 capacity, or a, &, and f, the three principal velocities of propagation, 

 we may write 



(24) 



In a non-conducting medium, where the electrical density is 

 constant at each point, the general equations of propagation become 

 then 



IT _AF-- 



1 a/2 3*~<j2 3/2 ' 



, ae 



(25 ) K = AG - 



ae 



If /, m, and are the cosines of the angles which the perpen- 

 dicular to a plane wave, moving with the velocity V, makes with 

 the axis, we may write 



Ix + my + nz- V/= o>. 



If we represent by F", G", H" the second differentials in respect 

 of a/ of the different functions F, G, and H ; equations (25) become 



/ V 2 - a 2 \ 

 ( + / 2 )F" 



V * 2 / 



/V 2 - tf \ 

 (26) ^- 





(V 2 -^ 2 

 - 

 ^ 2 



