PAPERS OX CHEMISTRY AND PHYSICS 



273 



miitiial conductances and amplification constant of three 

 of these tubes were measured by Van der Bijl's methods 

 for varying plate voltages and the results plotted in Figs. 

 7 and 8. It should be noticed that the mutual conductance 

 is high for low plate voltages and falls off gradually 

 (See Fig. 7) as plate voltage increases. This constant in- 

 creases gradually with filament temperature. The sam- 



■-•j^ -S -i. -/ O / 2, 5 7- S 6 7 8 



pie curves A and B of Fig. 7 show the variation of this 

 constant for gas content tubes and high vacuum tubes re- 

 spectively. For a discussion of mutual conductance see 

 Van der Bijl, ''The Thermionic Tube". It is usually the 

 case that the tubes with high values of this constant are 

 good detectors, although they should also have high am- 

 plification constants and large change in the slope of the 



