420 Dr. Tyndall and Mr, Hughes on Cathode 



a simple, matter to obtain disintegration-time curves £01* 

 constant current and cathode-fall by varying resistance and 

 pressure accordingly. With copper electrodes the oxidation 

 trouble mentioned above prevented the work being carried 

 very far, and from this point onwards only platinum cathodes 

 were used. Three experiments were carried out with cathode- 

 falls 500, 600, and 800 volts respectively, the current in each 

 case was 3*08 milliamps. 



The results given in Curves 1 show conclusively that, 

 provided constant cathode-fall and current are maintained, 

 the rate of disintegration of a given cathode is constant from 

 the commencement of discharge. The apparent lag in the 



Curves 1, 



Ti M € {\rn minaiu) 



start of disintegration observed in many cases and cited 

 above is thus due to the relatively low value of cathode-fall 

 in the early stages of discharge under ordinary uncontrolled 

 conditions : it must, therefore, be regarded as a secondary 

 effect. In these experiments the pressure change during 

 discharge varied enormously (from 0*05 to 1*72 mm.) for 

 different readings, and the closeness with which the points 

 lie on straight lines may therefore be taken as confirming 

 the conclusions of (1) over a wide range. 



