30 



Proceedings of the Royal Irish Academy. 



With this measuring-tube three distinct bends on the current voltage 

 curve were determined, corresponding to mobilities -32, -092, and -043 cms. 

 per second. With the larger measuring-tube previously used the slower ions 

 were examined, and two groups were found with mobilities "0064 and '0022 

 cms. per second. With a third measuring-tube of intermediate size the 

 portion of the curve corresponding to mobilities between -043 and -0064 was 

 examined, but found to be free from bends, showing that there were no groups 

 of ions with mobilities between these values. 



We have, therefore, five distinct groups of ions with mobilities : — 

 •0022, -0064, -043, -092, and -32. 



The ratios of these mobilities are : — 



1, 2-9, 19-5, 41-8, and 145. 



These numbers are the means of several observations, which showed fairly 

 good agreement. 



VoU's 

 Fig. 4. 



As the ionization was greater under the present conditions, we were able 

 to make observations on both positive and negative ions, and in the case of 

 all the five groups the ions of different signs were found to have equal 

 mobilities. 



The mobilities given above are greater than the corresponding numbers 

 when a longer time interval was allowed. Probably even larger numbers 

 would have been found if the measurements had been made with a still 

 shorter time interval. 



