Disintegration in a Vacuum Tube, 



419 



is negligible, and this assumption seemed to be justified 

 by some observations by the former on cathodes of different 

 size with which constant current density and cathode-fall 

 were maintained. 



The authors have confirmed this in two ways. In the 

 first place observations were made on the changes of pressure 

 during discharge from a given cathode at constant cathode- 

 fall (V), current (0), and duration (t). It was found that 

 the rate of disintegration was independent of the limits 

 between which the pressure varied during discharge. The 

 results taken alone, however, are not conclusive because, 

 owing to the conditions of experiment, the range of pressure 

 variation was necessarily very limited. A typical set of 

 results is given, however, in Table II. 



Table II. 



Platinum Cathode. 



V = 800. C = 3-08 milliamps. £ = 30 minutes. 



Pressure in mm. 



Disintegration in nigs. 



Initial. 



Final. 



•08 

 •OS 

 •07 

 •08 



•22 



•27 

 •35 

 •40 



3-5 

 33 

 34 

 35 



The strongest evidence, however, is obtained by the second 

 method, in which the duration of the discharge was altered. 

 These experiments are detailed below and show that the 

 direct effect of pressure is negligible over a very wide 

 range. 



(2) Experiments with both copper and platinum cathodes 

 showed that, provided constant cathode-fall was maintained, 

 the disintegration was the same within the limits of experi- 

 mental error (a) whether the wire had or had not been used 

 previously as a cathode, and (l>) whether it was discharged 

 from immediately after being placed in the tube or after a 

 lono- interval in vacuo. 



(3) As the result of the experiments of (1) and (2) it was 



