﻿344 Prof. Trouton and Mr. Searle on Leakage Currents 



took place so as to bare the glass the angle of polarization 

 should alter. No such effect was observed. 



The second method depended on the relative alteration in 

 path o£ two interfering beams of light. If the rays are 

 arranged to pass through the grid one near, say, the positive 

 electrode and the other near the negative, then on putting the 

 current on a change in path should be observed. In this case 

 also no effect was found to occur. 



Ohm's Law examined for Surface Conductivity of Condensed 

 Moisture on Glass. 



The occurrence of the great differences in value of the 

 currents obtained on reversal might be due, as some have 

 supposed *, to a back-E.M.F. comparable in amount with the 

 impressed potential-difference, or C= (E — e)/R, where e is 

 comparable with E. 



With the view of tracing the matter out, experiments were 

 undertaken to determine the relation between E and C. 

 Various electromotive forces were applied to a grid and the 

 corresponding currents observed. As much care as possible 

 was taken not to leave the current on longer than was abso- 

 lutely necessary to make a reading, so that the grid might 

 remain as nearly as possible in the one state of sensitiveness 

 throughout the determinations. In spite of all, variations 

 occurred ; this could not be helped, for the testing current of 

 course must in some manner alter that state of sensitiveness. 

 In interpreting the results this variation must be allowed for. 



Two hundred small accumulator-cells were used and were 

 arranged so that 400, 350, 300, &c. down to 50 volts could 

 be quickly switched on to the grid. The results are shown 

 in Table IV., and are plotted in fig. 4. The first six curves 

 were obtained one after the other by switching on the cells 

 always in the above order. The resistance is seen to increase 

 slowly from curve to curve. This could not be prevented, 

 as already mentioned. But there is also, apart from this, a 

 greater resistance, or ratio of E/C, shown for the smaller 

 currents along any one curve. 



To further test this result, the cells were now applied in the 

 reverse order so that, as the resistance on the whole is creeping 

 up, the alteration in sensitiveness would act in the opposite 

 direction to the effect of this departure from Ohm's law. 

 Curves VII. and VIII. so obtained confirm the sign of the 

 departure from linearity, and show that within the range of 

 the voltages used the ratio of E/C diminishes as the current 

 increases. 



* Electrician, vol. lvi. p. 952. 



