780 



Mr. S. G. Lusby on the 



In fiof. 2 the logarithms of the currents are plotted against 

 the corresponding temperatures. It will be seen that the 

 linear relation connecting these two coordinates is very close. 



Fijr. 2. 

 Current and Temperature. 

























2 

 1-5 































































0-5 





o 



o 





































1000 



1400 1500 1600 1700 



TEMPERATURE ABSOLUTE. 



1800 



1900 



This suggests that the current increases with the temperature 

 according to an exponential law. The values for the current 

 at the two lowest temperatures do not lie on the curve. This 

 is due to the fact that these two values were obtained with a 

 different cathode, whose mesh was finer than in the other 

 case. 



(5) Determination of Potential Gradient. 



The minimum potential gradient in the flame was deter- 

 mined in the way indicated previously *. In most cases a 

 quadrant electrometer of low sensitiveness was used. A 

 constant potential-difference was maintained between the 

 quadrants, whilst the search-wire in the flame was joined to 

 the needle. The instrument used gave deflexions directly 

 proportional to the potential up to 120 volts. 



The readings were remarkably constant for the salted flame, 

 but not quite so good for the pure flame. The potential- 

 difference applied between the two electrodes in the flame was 

 that found experimentally (see fig. 1) ; it was the minimum 

 required to drive back the positive ions against the flame 

 gases. 



* Proa Camb. Phil. Soc. i. p. 26 (1910). 



