23 Proceedings of the Hoyal trish Academy. 



separate iu itself, if the process of foUowing up the chain from the slowest to 

 the fastest ion had not been carried out, we should come to the same conclusion. 

 All these measurements, made under widely different conditions with regard 

 to time, fall into a certain limited number of distinct groups. There cannot, 

 therefore, be any gradual changing of mobility from one group to another ; 

 there is no change from .013 to -0043 (Group 4 to Group 8), for if such a 

 change occurred, intermediate values must have been observed in some of 

 the experiments. These conclusions have special force in the slower groups 

 (Group 2 excepted), because their strength depends upon good agreement 

 between the values for mobility within the groups and the absence of inter- 

 mediate values. With the exception of Group 2, these conditions are 

 satisfied in the case of the slower ions. In the more mobile groups the gaps 

 between the groups arc small, and for some of the groups satisfactory obser- 

 vations have not been obtained in great numbers. The occurrence, therefore, ' 

 of the mobilities '67, "8, 23, &c., tends to weaken the group system. There 

 may be a special reason for the occurrence of these anomalous mobilities. 

 Furtlier investigation by a more accurate and rapider method than that 

 employed in this work should clear up the point. The group system has been 

 well established in the case of the slower ions, and, in spite of the anomalies ~ 

 that have been mentioned, it may be considered as hardly less firmly established 

 in the case of the more mobile ions also. 



The results obtained from these observations of the ionisation produced 

 by spraying distilled water bear a very close relation to those obtained from 

 experiments on the bubbling of mercury, which are gi^'en iu the paper 

 immediately following by Professor il'Clelland and Mr. P. J. Nolan. 

 Consideration of the results of this paper are therefore deferred. A joint 

 discussion of the combined results is given at the end of the next paper. 



[Summary of Kesults. 



