McCi.KLLAND AND NoLAN — loHS Produced through Mercury. 29 



exist. The means of a number of observations of the type illustrated by these 

 curves gave the following mobilities : — 



•00034, -0013, -OO-i, -014 



The ratios of these mobilities are . — 



1 8-8 11-8 41. 



As stated above, all the observations in this section were with positive 

 ions, except in the case of the slowest group, in which ions of both signs were 

 measured, and found to have the same mobility. 



Dried Air. 



The air was now passed through drying tubes before reaching the 

 mercury, and the same time interval allowed between the bubbling and the 

 measurements as in the above experiments with undried air. 



One result of drying the air was to reduce the amount of ionization to 

 about one-sixth of its value with undried air. 



The mobilities were greater than with undried air, although the time 

 interval was equally long. Measurements of the mobilities made at different 

 times did not now show such a satisfactory agreement, possibly because the 

 degree of dryness on different occasions was not the same. One set of 

 experiments gave the following mobilities: — 



•00056, -0021, -0068, -024 cms. per sec. 



The ratios of these mobilities are : — 



1, 3'8, 12-1, 42-8. 



The observations to which these numbers refer were made with positive 

 ions only. 



The question arises as to whether these ions had reached constant 

 mobilities, or whether they were still decreasing in mobility towards the 

 values found in the preceding section. Our observations show that after the 

 interval of time allowed the mobilities, if not constant, were changing very 

 slowly. 



Dried Air. Mobilities measured before stable condition was reached. 



Continuing to use dried air, we now measured the mobilities as soon as 

 convenient after the air bubbled through the mercury. As higher mobilities 

 were now found, we used a measuring-tube with a shorter inner terminal. 

 The dimensions of the apparatus and air-blast were such that about 

 10 seconds interval occurred before the measurements were made. A 

 careful examination of the air showed that the fastest moving ion had a 

 mobility of ^32 cms. per second. 



