466 Prof. F. Horton on the Application of Thermionic 



Suitable thermionic currents were obtained with this electrode 

 at temperatures of 900° C. to 1000° C. The thermionic 

 currents were measured by means of a sensitive d'Arsonval 

 galvanometer, which was arranged in the circuit as shown 

 in fig. 2. 



Fig. 2. 



A. Upper plate. B. Lower plate. G. Galvanometer. 



The galvanometer was insulated on paraffin blocks and was 

 connected to the movable plate A and to the positive terminal 

 of! a high potential battery, the negative terminal of which 

 was connected to earth. The lower plate B was also con- 

 nected to earth. It is desirable that the part of the glowing 

 filament which is exposed in the plane of the plate B should 

 be at the same potential as that plate. This equality cannot 

 be obtained along the whole length of the 1 mm. of strip 

 exposed, because the heating current has to be maintained, 

 and there was a drop of *05 volt along it due to this cause, 

 the total difference of potential between the two ends of the 

 strip being about *5 volt. The potential of the middle point 

 of the exposed portion of the hot strip was kept at zero by 

 shunting the strip with a high resistance and earthing this 

 resistance at its middle point. That the desired equality of 

 potential of the plate B and the spot of lime on the hot 



