ARMSTRONG, OPERATING FEATVREi^ OF THE WD] ON 217 



rent. Investigation sliowecl that this was due to the charge accumulating 

 on the grid when exposed to bombardment by the electrons passing fro'itL- 

 the filament to the wing. The electrons pass readily enough into the 

 grid but cannot easily escape from it, and as a consequence of this, nega- 

 tive electricity piles up on the grid. The potential assumed by the grid- 



es 



Fbtent/alof 

 Qridmth . 

 respectto 

 Filament 



Wing 

 Current 



Fig. 4 



when exposed to this bombardment may be several volts ■ negative with, 

 respect to the negative terminal of the filament, it ma}^ be the same aS 

 the negative terminal, or it may be positive with respect to the negative 

 terminal, but it will always be negative with respect to the potential of 

 the field in the plane of the grid which would exist if the grid were re- 

 moved from the bulb. The uegative charge on the grid, therefore, 



.^I'd-js^^likL^^. 



y/tn<f Ctirrrrtf 



Pig. 6 



impedes the flow of electrons from filament to plate, causing the decrease 

 in the wing current. The placing of a positive charge on the grid from 

 an external source tends to neutralize the negative charge on the grid, 

 thereby permitting an increase in the wing current. The addition of a 

 negative charge to the grid increases the deflection of the electrons aiid 

 produces a further decrease in the wing current. 



