44 Proceedings of the Royal Irish Academy. 



the second apparatus we used an accelerating field of ten times this value. 

 This we think is the real cause of the difference. Experiments on this 

 point are now proceeding. 



"We give below a table of all the mobility values in dry air. "We have 

 not included any of the results got by the second apparatus ; but, as will be 

 seen from the figures quoted above, they are in very good agreement, as far 

 as they go, with the results got by the first apparatus. On examining the 

 table it will be seen that there is some disagreement as to the correct value 

 for one of the ions. The positive values are 8-0, 8'32, and 8-6. A negative 

 value is S'll, and the second apparatus gave 7'9. Some of our observations 

 suggest that there are really two ions here, one of mobility about 8, and the 

 other having a value between 8-5 and 9. 



Mobilities in Dry Air. 













Positive. 







24-6 



12-3 



8-0 



5-56 



4'45 



2-91 2-53 



2-26 



2-0 1-82 1-60 1-40 



24-8 



12-3 



8-32 



5-61 



4-30 



3-II 2-60 



2-28 



2-05 1-82 I-oO 1-39 





12-4 



8-6 



0-73 





3-14 

 Negative. 



2-32 



2-02 1-78 



24-8 



12-1 



8-11 



5-56 



4-42 



3-0 2-5 



— 



_ _ _ _ 



24-1 



12-1 

 12-3 

 12-6 









3-02 2-5 

 3-09 







Mean values, Positive 



iind Negative : 



24-6, 12-3, 



8-2, 



5-61, 4-39, 304, 



Positiv 



e only : 



2-29, 



202, 



1-81 



, 1-55, an 



d 1-3E 



1 



2-53 



Possihility of the Presence of Free Electrons. 



In view of the great changes produced by long drying, it seemed to us 

 possible that free electrons might be present in the dry gas. "We have 

 therefore endeavoured to determine the exact voltage at which the current 

 begins to rise from zero values, using the second apparatus. At low voltages 

 the current values are very small, and it is difficult to obtain consistent 

 readings. Prom observations made on a number of occasions, when conditions 

 were fairly steady, we believe that the current begins to rise at some voltage 

 between 25 and 30. Two specially good observations give 27"5 and 28 volts. 

 As the constant Vu for this apparatus is 3,225, this would indicate a 

 mobility of about 115. "We consider it probable then that free electrons 

 are present in very small quantities. The mobility value which we find is, 

 however, much smaller than that usually quoted for gases such as nitrogen. 

 As the free electron in this apparatus, after passing through the perforated 



