Contact with. Dielectrics. 



493 



reduction of thickness due to the heavy load. It was If cwts. 

 on a 5-J inch disk. 



The next experiment was made with a view to testing the 

 resistance with tinfoil electrodes, as nearly as possible under 

 the same conditions as those adopted by Mr. Rayner. For 

 this purpose the sheet was allowed to rest for 17 J hours. It 

 was then put into the apparatus, and the weights on the disk 

 area of 153'3 cm. 2 were adjusted to give a mean load of 

 400 grammes per cm. 2 Five minutes was then allowed, as 

 in Mr. Rayner' s experiments, for the conditions to become 

 steady, before applying the voltage. Only one minute was 

 allowed between the successive voltages. The readings and 

 results were as follows : — 



Table VI. 

 Tinfoil Electrodes. 



1 



Volts. 



Shunt, 

 ohms. 



Deflexion, 

 1 min. 



Deflexion, 

 2 min. 



Megohms. 



+ 150 



1000 



266-5 



266-5 



17 6 



+ 750 



140 



240-0 



238-0 



149 



+ 150 



1000 



284-5 



283-5 



16-5 



+750 



140 



237-0 



235-5 



150 



The results are fairly uniform, but the diminution of re- 

 sistance with increase of volts is still marked. 



For purposes of comparison, the dielectric sheet was then 

 immediately placed in the mercury apparatus, and tested in 

 precisely the same way, with the following results : — 



Table VII. 

 Mercury Electrodes. 



Volts. 



Shunt, Deflexion, 

 ohms. 1 min. 



Deflexion, 

 2 min. 



Megohms. 



150 

 750 

 150 

 750 



1000 342 



140 259 



1000 332 



140 255 



1 



339 

 255 

 331-5 

 252-5 



13-7 

 138 

 14-1 

 140 



A comparison between Table VI. and Table VII. seems to 

 indicate that although the tinfoil electrodes under a load of 

 400 grammes to the cm. 2 , and with an allowance of 5 minutes 



