Nolan — Ions prodvccd in Air hi) Rudio-Active Bodies. i\ 



Eesults. 

 'I'he type of curves obtained in lliis wink will be clear from an inspection 

 of lig. '1 and fig. 3. Figure 2 is an example of the first part of the current- 

 voltage curve, starting at zero voltage. Instead of a smooth slope upwards, 

 we find a curve broken by four slight but unmistakable "nicks" or changes 

 of direction. This indicates the presence, in small quantities, of four distinct 

 classes of ions. The mobilities of these ions can be calculated from the 

 formula Fw = QalLb, where V is the " critical voltage," ?t the mobility, 

 Q the volume of air per second, a the distance between the plates, L the 

 length of the upper plate, and h the width of the apparatus. In all the 

 experiments for which graphs are given, Vu had the value 250. The critical 

 voltages on this curve are 2, 3-75, 6, and 8-35, and these values correspond to 



Fig. 2. 



ions of mobilities 12'5, 6'66, 4'16, and 3'0 cm. /sec. The graph given refers to 

 negative ions. Similar graphs ai-e obtained with positive ions, and, as far as 

 investigation has gone, there seems to be no striking difference between the 

 nature of ihe ionization of the different signs ; certainly the ion of the 

 highest mobility (12'5) is present in the positive ionization. 



With regard to the curve given, it may be as well to state — and this 

 applies equally to tiie other two curves— (1) that all the points plotted are 

 direct experimental numbers, and are not the result of taking means ; and 

 (2) that every observation taken has been plotted. 



In fig. 3 are given two examples, negative and positive, of the continua- 

 tion of the current-voltage graph. Here, instead of the rather slightly 

 marked "nicks" of the first part of the curve, we find in each case four dis- 

 tinct and well-marked steps. This indicates the presence, in considerable 



