48 



THE ROYAL SOCIETY OF CANADA 



It is of interest in connection with these readinfjs to note that the 

 conductivit}' obtained with the negative fields was practically the same 

 as that with the positive. This agrees with the results obtained by 

 Greinacher in the ionisation of petrol ether by alpha rays. As pointed 

 out before, Greinacher in the case of his experiments has drawn the 

 conclusion from his results that the positive and negative ions taking 

 part in the conductivity impressed upon petrol ether l)y alpha rays 

 have to a very close degree the same mobility. But from some experi- 

 ments to be described later, it will appear that this conclusion can 

 scarcely be drawn from the results obtained in the licjuid air experiments 

 just described. 



IV. Ionisation in Air at High Pressures by Alpha Rays. 



In another set of measurements the system MH, LE, and KD 

 with the polonium coated plate AB in position, Fig. 3, was placed in 

 a receiver with thick steel walls and air was pumped into it until a 

 pressure of 101 atmospheres was reached. A set of readings similar 

 to those obtained when the above system was immersed in liquid air 

 was then taken, ]3Ut in this case, owing to the much greater conductivity 

 which was obtained, a set of sulphur condensers was connected in series 

 with the free quadrants. The whole capacity in this case including 

 quadrants, electrode, condensers, and leading wires was 3635 e.s.u. 

 The readings taken with both positive and negative fields are given 

 in Table IV and the curve corresponding to them is shewn in Fig. 5. 



TABLE IV. 



Conductivity impressed upon air at 101 Atmospheres by the Alpha Rays from 



Polonium. 



