[mclennan-keys] 



ELECTRICAL CONDUCTIVITY 



45 



voltages , in the current through the presence of the polonium 

 in the liquid air. In this particular set of measurements the 

 capacity of the electrode and the system connected with it was 

 about 200 e.s.u. and the distance between the electrodes A and B was 

 about 5 mm. 



From the form of the curve it will be seen that even with the 

 highest voltages used saturation was not obtained. There is, however, 

 a distinct bend shown in the curve in the region corresponding to 

 about 150 volts. 



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Fieié Potent,!,! 



Figure 2 



It is difficult to give a complete explanation of this bend; but in 

 all probability the phenomenon has to do either with a volume ionisation 

 produced in the liquid air by some unknown radiation of a penetrating 

 type from the polonium, or by beta rays due to some active impurity 

 in the polonium. Possibly too it may have been due in part at least 

 to a diffusion of ions into the body of the liquid air from the thin layer 

 of ionisation produced by the alpha rays close to the plate B. It is 

 clear that moderate fields would in all probability suffice to remove 

 all such ions from the field and so account for the bend. The gradual 

 rise in the curve obtained with fields about 200 volts was no doubt due 

 to the increasing influence exerted by the field in overcoming recom- 

 bination in the ionised layer of liquid. 



