323 ANNALS NEW YORK ACADEMY OF SCIENCES 



To make use of the "valve" action between hot and cold electrodes for 

 the detection of high-frequency oscillations a connection as shown in Fig. 

 13 is used. In this case a condenser C^ is inserted somewhere in the 

 circuit between the grid and filament to prevent the flow pf a continuous 

 current between them, and the grid is therefore left free to assume a 

 potential determined by its position with respect to the filament and 

 wing. Usually this will be somewhere near the center of the operating 

 part of the curve in Fig. 1 ; that is, near point P. ISTow the action for 

 incoming oscillations, as far as the closed oscillating circuit, filament, 

 grid and condenser C2 are concerned, is identical with the rectifying 

 action of the Fleming valve. An incoming wave train sets up oscilla- 



/^/e/ff/a/of 

 Grid with „ 



resfiecttS* 



rirament 



\N^r-^'^\s\^' 



^^ "Vv.-/'^^.^ 



Te/e/jhom 

 Current 



Fig. 14 



tions in the closed circuit LG which are rectified by the "valve" action of 

 the filament and grid, and the rectified current is used to charge the con- 

 denser Cg. Electrons pass readily enough into the grid, but cannot easily 

 escape therefrom, and a negative charge is built up on the side of the 

 condenser connected to the grid. The negative charge thus imparted to 

 the grid cuts down the flow of electrons from the filament to the wing, 

 producing a decrease in the wing and telephone currents. At the end of 

 a wave train the charge in Cg gradually leaks off and the wing current 

 returns to its normal value. The charge and discharge of this condenser 

 take place in the manner indicated in Fig. 14. 



One group of oscillations produces a single low-frequency variation 

 (decrease) in the telephone current and a series of wave trains produces 

 a corresponding series of low-frequency variations in the telephone cur- 

 rent. In Fig. 15 is shown an oscillogram of the behavior of the audion 

 when the "valve" action is employed for the detection of oscillations. 



