E. 31. Wellisch — Mobilities of Ions in Air. 593 



All the curves corresponding to the negative ion at pressures 

 below 8 cm were of the same type as that exhibited in tig. 5. ^ A 

 set of curves obtained is shown in fig. 7 ; the frequency of field 

 alternation was practically the same for each of these curves and 

 consequently a comparison can be readily instituted between 



Fig. 



20 



4(1 



60 



80 



100 



120 



Volts 



them. In order to avoid undue complication, the points from 

 which the curves were drawn are not given, but in every case 

 the curve was drawn smoothly through a large number of 

 points. For purpose of illustration, the actual observations 

 from which curve C (p = 1*69) was drawn are recorded below. 



