Nolan and Harris — lonisation in Moist and Dry Air. 39 



curves obtained are given in fig. 4. For voltages less than about 50 the 

 current is zero. Then it begins to rise, the slope increasing sharply at four 

 points, indicating the existence of ions of four mobilities. These four mobi- 

 lities correspond, within the limits of experimental error, to the four ions 

 present in greatest quantity in saturated air, as determined by the other 

 method. The fact that the curves begin to rise at about 50 volts (the exact 



Fig. 4. 

 lonisalion curves in iindiied atmospheric air, altei'nating-field method, showing positive 



and negative ions of mohilities 2-5, 204, 1-73, l-o4, and 1-42. 

 (negative) for saturated air does not show ion of mobility 2'5. 



Upper cnvve 



determination of this voltage is somewhat difficult) shows that there are 

 also present ions of mobility about 2-5 or 2-6. The fact that no current is 

 obtained at lower voltages shows that the faster ions found by the other 

 method are absent, or perhaps present only in very small quantities. The 

 negative curves rise much more steeply than the positive. The agreement 

 between the different curves is fairly good. 



