84 



Proceedings of the Royal Irish Academy. 



casual irregularities is easily seen when the lower parts of the curves are 

 examined more closely. We will consider in detail the examination of the 

 positive curve. 



If the region between 300 and 400 volts is examined working with reduced 

 capacity in the electrometer system, curve A of fig. 4 is obtained. Here we 

 find a sharp change of slope occurring at a voltage of 352. We deduce the 



presence of an ion of mobility tj^tt = 5-23. Curve B covers the range 



from 260 volts to 350 volts. Here we find another sharp change of slope 

 occurring at 299, corresponding to an ion of mobility 615. 











1 ^ 



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/ 



1 









/ 

 / 

 / 



/ 









1 



1/ 



1 



















/ 









/ 









/ 



/ 







/ 



/ 















Volts 



B 



I 









/ 











/ 









1 











/ 









J 









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/ 







?/ 



/ 















K>» 



A 



Fig. 4. 



There is a tendency for the upper part of the curve to be concave upwards 

 which is not so noticeable in the lower part of A, which covers the same 

 range. The scale of B is three times as open as that of A, so that it is natural 

 that the effect, if genuine, should be more noticeable with B. Now a concavity 

 in the curve must mean the access of new ions. It is possibly due to a 

 group of ions the critical voltage for which (as shown by the dotted line in B) 

 is 324. We may accept, then, with some reserve a subordinate group of 

 mobility 5-68. In fig. 5 the rest of the current-voltage curve is given in two 

 parts, C and D, plotted once more to different scales. Curve C gives an ion 



