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ANNALS NEW YORK AVADL'ilY OF SCIENCES 



potential of the grid with respect to the filament was varied in step be- 

 tween — 10 and +^^ volts, by means of the potentiometer P, correspond- 

 ing readings of the grid voltage and wing current being taken in order 

 to jjlot the curve of Fig. 1. The characteristic shows that, starting with 

 the grid and filament at zero potential difference, a negative charge im- 

 parted to the grid produces a decrease in the wing current and a positive 



GRID POTENTIAL 



Fig. 1 



charge imparted to the grid produces an increase in the wing current. 

 This is the fundamental action of the audion when used either as an 

 amplifier or a detector. The reason for this action will appear upon ex- 

 amination of the beha\'ior of an audion of the type shown in Fig. 3. 

 The wings of the audion were placed symmetrically with respect to the 



8.:= 



= B2 



wing Current = 

 4 Miliiamperes 



Wing Current 

 = 08 M)iliamperes 



Fig. 2 



Fig. 3 



filament, but only one grid was employed. It was found that, under 

 similar conditions of filament temperature and voltage of the battery B^, 

 a considerably smaller current was obtained between the filament and 

 plate on the side in which the grid was inserted. In both measurements 

 the grid was left entirely free of any connection with the rest of the ap- 

 paratus. Obviously the grid obstructed the flow of the thermionic cur- 



