134 Prof. W. M. Thornton on the 



If then, AC, BD take time to establish there is for a moment 

 a distribution of charge as in ii. fig. 5. In the end C moves 

 to C, D to D', for the viscous polarization has first to be 

 wiped out and then established in the opposite direction ; 



Fig. 5. 



"^k^^-s^— X,_J2- : 



F 



-3- 



ii c' a^ c Id „ B J> 



11. ^" [ , ' * i t • ■ — - 



but the condition at reversal is that the charges at C and D 

 are separated by a smaller amount than if there had been 

 no viscosity. The internal restoring force varies directly as 

 the separation of the charges and the displacement increases, 

 until when C and 1) are at their full outward positions a is 

 greater than it would have been if AC and BD could have 

 been also instantly reversed. In other words, because of a 

 viscous displacement AC superposed upon an elastic dis- 

 placement OA, a smaller field and less work produce the 

 limiting displacement, and breakdown eventually occurs at a 

 lower voltage. 



6. Intensity of Internal Field, 



From equation (2), v= —~ —a, or the breakdown voltage 



is less by the term representing interattraction. The value 

 of a is A/2B volts, since 



K — haj^irw^ and B = k 8irw. 



a is not the gradient but the equivalent applied voltage,, 

 that which would cause the same polarization as is in fact 

 produced by the interattraction. 



This inner field is in every case but paraffin greater than 

 the applied field, as shown by Table IX. 



The external breakdown voltage, therefore, although it 

 roughly differentiates between good and bad insulators, gives 

 no indication of the atomic forces under which a material 



