between Plates for small Distances. 



151 



It was found that the apparent resistance of the dielectric 

 depends in a measure upon the manner in which the potential- 

 difference is established. A sudden rise in potential from 

 zero up to a definite amount will cause a spark to jump 



Fiffs. 1 & 2. 



a considerably greater distance than if the potential were 

 built up gradually. This is perhaps what might be expected ; 

 for if we regard the energy due to the presence of the 

 electrified bodies as existing as a strain in the separating 

 medium, then the sudden application of such a strain would 

 cause the medium to break down more readily than if the 

 strain were applied gradually. The readings given in the 

 table are those in which the potentials are built up gradually, 

 or, what amounts to the same thing, a given difference of 

 potential being established, the plates were made to approach 

 one another gradually, thus confining the strain to a more 

 limited portion of the dielectric. It is for this reason that 



