PAPERS OX CHEMISTRY AXD PHYSICS 275 



or more ou the plate. The variation of signal intensity 

 with filament current is like that for high vaeumn tubes, 

 the intensity gradually increasing until the filament is at 

 very high temperature, and then gradually decreases. 

 The maximum received signal intensity seems to be from 

 3 to 5 times as great as for the same type of tube filled 



with argon or neon. This comparison was carefully made 

 and results were practically the same for the three tubes 

 tested. 



In all of the tests a variable grid condenser was used 

 in series with the grid together ^vith a grid leak of 2 

 megohms. This always gave at least as good audibility 

 as any applied negative grid potential, except for mer- 

 cury vapor filled tubes, in which a positive grid potential 

 was used. 



