470 Mr. J. J. Lonsdale on the Ionization 



saturation current for the positive ionization was only 20 mm. 

 divisions in 20 seconds. The current due to the negative 

 ionization when the first electrode was earthed could not be 

 observed, yet when the field was put on the first electrode 

 a current of 5 divisions was found. This appears to show 

 that the field produces the ions from the doublets, if such are 

 present. The initial leak of the electrometer could not be 

 observed : it was certainly less than 1 mm. in 20 seconds. 

 Examining these results, if we presume that they are due to 

 slow ions, then from the dimensions of the apparatus the 

 mobilities of both the positive and negative ions must be 

 less than '0018 cm. per volt-cm. It is worthy of note that 

 no matter how largely the total current C may differ in a 

 given pair of observations for the positive and negative ions,, 

 c is practically the same for either sign. This is what we 

 should expect if the current is due to the breaking up of 

 doublets. 



The saturation curve with negative ions is shown on fig. % 

 curve B. No departure from the usual form of saturation 

 curve was found with these ions, but the smallness of the 

 current may account for this. The second flat part does not 

 always appear even with positive ions. Whenever this is 

 missing, then all the ions can be taken out on the first 

 electrode by a voltage of about 100 volts. 



The ionization currents vary with the height of the drop, 

 the other conditions remaining the same. The investigation 

 was made in the following way : — A definite height of drop 

 being taken, the current for positive and negative ions was 

 observed on the second electrode with the first earthed. 

 Then a voltage of 114 volts was placed on the first electrode. 

 As this voltage is on the flat part of the curve first occurring,, 

 the faster positives will be driven on to the first electrode. 

 If the highest voltage is then placed on the second electrode, 

 the ions giving rise to the upper part of the curve will be 

 driven on to the electrode. The results averaged and 

 reduced to a sensitiveness of the electrometer of about 

 1000 mm. per volt are given below : — 



Height of dropper H cms. 



Voltage on the first electrode V t 



Voltage on the second electrode V 2 



The total current due to negative ions N 



The total current due to positive ions P 



The positive current when the voltage Y 1 is on the 



second electrode p 



