fMCLENNAN-KEYS] 



ELECTRICAL CONDUCTIVITY 



49 



The curve it will be seen is in this case practically of the same form 

 as that obtained with the ionisation impressed by the rays upon liquid 

 air, and it would appear that here too the form of the curve has its 

 explanation: (1) in the formation of ions in the body of the air 

 by some unknown radiation of a more penetrating nature than 

 alpha rays from the polonium coated plate or by the diffusion of 



300 *so 



600 TJO 



Figure 5 



lOSO /SÛO IJSO 'SOO 



Field PolhntiAlltK.t^oZt^. 



ions from the thin ionised layer close to the one electrode into the 

 space between the two electrodes, and (2) in the gradual lessening 

 of recombination by the applied fields. As the numbers shew, the 

 currents with positive and negative fields just as in the liquid air 

 experiments were practically the same. In seeking for an explanation 

 of this result one must bear in mind the work of Kovarik* and of 

 Dempster f on the mobilities of ions produced by alpha rays in gases 

 at high pressures. 



In his paper Kovarik * has shewn that with the air used in his experi- 

 ments the mobilities of both kinds of ions varied inversely as the pressure 

 from one to seventy-five atmospheres, and that for the same range of 

 pressures the mobility of the negative ion was about 1«4 times greater 

 than that of the positive. Dempster's f results, too, shew that at 100 

 atmospheres the mobility of the negative ion in air was about twice 



*Kovarik, Proc. Roy. Soc. A. Vol. 86 p. 154. 

 fDempster Phys, Rev., Vol. XXIV, No. 1, 1912, p. 53. 



