56 



Proceedings of the Royal Irish Academy. 



has been confined to a few volts. We shall now give the results of experi- 

 ments showing how the current varies with the E.M.F., both in the case of 

 fresh layers and of layers which have had their conductivity greatly increased 

 by the application of the transverse field. When measuring the current for 

 larger voltages, it was necessary to examine in the first place whether the 

 application of such fields along the layer produced an increase of conductivity 

 which would persist after the removal of the field — whether, in fact, the 

 same effect would take place as when the field was applied transversely through 

 the dielectric. It was found that the electromotive forces used in measuring 

 the current — up to 200 volts — produced no such effect, the current being the 

 same whether the E.M.F. was applied suddenly or in small steps. There is, 

 however, one exception to this statement. It was pointed out in section 5 

 that a layer which had been exposed to a large transverse field, and which 

 had been given time to lose most of its increased conductivity, was specially 

 sensitive when again exposed to a transverse field. We now found that such 

 a layer was sensitive also to fields applied along the layer, and the sudden 

 application of, say, 200 volts along the layer, gave a greater current than the 

 same E.M.F. applied in small steps. 



-9 



1*10 



^ 



Volts. 



Fig. 



The relation between current and E.M.F. is shown in fig. 5, curve A, for 



