54 



Proceedings of the Royal Irish Academy. 



Table He were obtained working at a pressure of 7 cms. of mercury, and 

 those in Table IK with a pressure of 11 cms. 



Table Ha. 





•04<J 



•020 





•0074 







•056 



020 





•0076 







050 



■014 





0067? 







055 



■014 P 





0071 







•040? 



■016 :• 









Mi i\-. 



- 



•018 



■0074 









Table [16. 











•016 





•0072 



0032 











■0071 



0040 













•0037 



Mian-. 



•043 



■"17 



0072 



•0036 



A few curves svitli .i pressure oi 4 cms. of mercury were taken, and the 

 ace "i -in i"ii of mobility - '12cm./sec. was observed. 



I : ■ :■ i results n i- seen that the division into types of ions is further 

 justified, and that change ol pressure does nol change the mobility of any of 

 these ions. [n< reasing the pressure causes the appearance of types of ions of 

 lowei mobility iu<\ the disappear. mee "f the faster ions. 



Iln' t"t.il ionisation, as de Broglie has found, increases as the pressure 

 increases. From these measurements of mobilities at different pressures, it 

 appears thai this increased eli in is due to the increased production 



of slower ions. The disappearance of the faster ions may be only apparent. 

 rhey in. iv be present at the higher pressures in much the same quantity as 

 the lower pressure, but the large increase in the total quantity of ionisation 

 may conceal them. It is difficult to decide on this point. With this method 

 of measuring mobiliti ially when there are so many classes of ions, it 



is difficult to determine accurately the fraction of any particular class present, 

 I he fraction of the ionisation due to any particular ion is got by producing 



two straight lines on the current-voltage curve, whose intersection 



rmines the saturation voltage of the ion, to meet the current axis. The 

 i by these lines on the current axis is the current clue to the 



