530 



E 

 vector E. The current density is then — . \i t be the time, the 



fundamental equations of the problem are : 



divH=0 curl H — ^ E (1) 



<j 



dH 



div E=0 curl E= — ^- (2) 



ot 



d\ 4:71 



Hence 



('■-4,) 



and in tlie case of cylindrical symmetry, H being parallel to the 

 axis, the distance from which is r 



( 



d' Id d , 



(31) 



If only small penetrations from the surface are investigated the 

 approximate form 



d'H dH 



= B — 



dr' dt 



(311) 



may be used. The equations (3), (3^), (3^^) are analogous to equations 

 in heat condiiclions and it is therefore of interest to follow out this 

 analogy somewhat closer. In the case of cylindrical symmetry and 



H parallel to the axis the electric 

 intensity is by symmetry directed 

 along a system of coaxial circles 

 having the axis of symmetry for 

 their common axis as shown on 

 the figure (Fig. 1). Dropping now 

 the meaning of E and H as 

 vectors and denoting forthwith 

 by E and H the absolute magni- 

 tudes of the electric and magnetic 

 intensities, we have from (1) 

 and (2) 



dH 



— —- — ^E. . 



1 d 



/>« /. 



{tE} = 



dH 

 'dt' 



(5) 

 (6) 



