hy Hot Platimim in Air at Low Pressures. 



93 



+ve Leak cc . 



Time. 



154 



inin. sec. 

 15 



18 



4 U 



9 



8 



6 



11 15 



4 



22 



It appears from these numbers that the rate o£ foiling off 

 is greater than at higher pressures. The difference may, 

 however, be due to a difference in the temperature o£ the 

 wire in the two cases. 



Activity induced hy the Luminous Discharge. 



In making experiments to see if the induced activity was 

 increased by increasing the potential-difference between the 

 two wires, it was found that an extraordinarily big effect was 

 ■obtained with —400 volts on the first wire. When the 

 experiment was repeated it was found that an ordinary 

 vacuum-tube discharge had been passing between the two 

 electrodes. Further experiments were therefore made with 

 both electrodes cold in order to see if the discharge produced 

 the effect even when the second spiral was not heated. 



The first wire was heated in the usual way until it gave no 

 leak with +200 volts and a heating-current of '35 ampere. 

 It was then allowed to cool, and raised to a potential of 

 — 400 volts^ the second wire being earthed. This difference 

 of potential was sufficient to produce a discharge which was 

 allowed to pass between the two electrodes for 60 seconds. 

 After waiting a few minutes the first wire was heated to the 

 same temperature as that at which it had been tested before, 

 and the leak was measured with + 200 volts on the first 

 wire. An induced activity of 500 divisions in 30 seconds 

 was observed. 



It was evident, as in the former case, that this effect was 

 not due to ions left in the gas by the discharge, since there 

 was no leakage of electricity from the first wire until it was 

 heated. 



An experiment was next made to see if the induced activity 

 would persist for 40 minutes if the wire was kept cold after 

 passing the discharge. As before, the wire was tested and 

 fomid not to leak with '35 ampere of heating-cui-rent. It 

 was then cooled and the discharge passed for 60 seconds. 



