Question of Valency in Gaseous Ionization. 



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the vast majority of all chancres of charge which the oil 

 drops experienced corresponded to the advent upon the drop 

 under observation of a single elementary electrical charge, a 

 few changes were observed, even when the field ivas on, which 

 corresponded to the advent of two or three such charges. 



It was of course recognized from the first that it is very 

 difficult to distinguish between the practically simultaneous 

 advent upon a drop of two or three separate ions and the 

 advent of a doubly or trebly charged ion, but a consideration 

 of the frequency with which ions were being formed in the 

 experiments under consideration seemed to render it impro- 

 bable that the few double or treble catches observed when 

 the field was on could represent the simultaneous advent of 

 separate ions. It was obvious, however, that the question 

 could be conclusively settled by working with smaller and 

 smaller drops ; for the proportion of double to single catches 

 made in a field of strength between say 1000 and 6000 volts 

 per centimetre should be independent of the size of the drops 

 if the doubles are due to the advent of doubly charged ions, 

 while this proportion should decrease with the square of the 

 radius of the drop if the doubles are due to the simultaneous 

 capture of separate ions. 



Accordingly, in the work herein described, we suspended 

 by the method detailed in the papers referred to, a very 

 small positively charged drop in the upper part of the field 

 between C and D (fig. 2), adjusting either the charge upon 



Fig. 2. 



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the drop or the field strength until the drop was nearly 

 balanced. We then produced beneath the drop a sheet of 

 X-ray ionization. With the arrangement shown in the 

 figure, in which C and D are the plates of the condenser 

 previously described, and L and 1/ are thick lead screens, 

 the positive ions are thrown practically at the instant of 

 formation to the upper plate. When one of them strikes 

 the drop it increases the positive charge upon it, and the 



