Section III., 1914 [177] Trans. R.S.C. 



Notes on the Thermionic Current in a Carbon Filament Lamp. 

 By A. S. Eve, D.Sc, F.R.S.C, McGill University. 



It has been shown* that a lighted carbon filament lamp, having 

 two loops, is affected by the movement of an electrically charged con- 

 ductor in a manner which proves that the current is mainly unidirec- 

 tional and is conveyed by electrons from the glowing filaments. 



In order to study this phenomenon further, Dr. Johnson was kind 

 enough to open a lamp, and affix a glass tube so that the globe could 

 be silvered inside by Mr. Pye; a platinum wire was passed through 

 the side of the globe and sealed hermetically, after which the lamp was 

 exhausted and sealed by Dr. Johnson. The lamp worked perfectly 

 well, except that it tended to heat rapidly when lighted, owing to the 

 silver deposit absorbing the heat. 



The platinum wire made good connection with the silver deposit on 

 the inside of the globe, but the silver did not make contact with the 

 leads to the carbon filament. 



Various experiments could be made with this lamp, many of 

 them analogous to those made by Fleming when he investigated the 

 thermionic current, or Edison effect. 



For example, if the silver deposit within, and the platinum wire 

 through the glass globe, were connected to a delicate galvanometer, 

 and thence to earth, a slight current was shown when the carbon 

 glowed red. When the voltage was 110, and the carbon was at a 

 white heat, the current increased several hundred-fold. 



If connection was made between the platinum wire and the 

 charged gold leaf system of an electroscope, the insulation remained 

 good; but when the lamp was lit, even at a low voltage, the gold leaf 

 collapsed immediately. 



By adding capacity, using a Leyden Jar or two, to the insulated 

 system, it was easy to show that the current from the dull red carbon to 

 the silver coating was unidirectional, for the gold leaf system closed at 

 widely different rates, according to the sign of the charge initially 

 given to it. 



A telephone was then connected, on the one side to the platinum 

 wire, and on the other side to the hot water pipes. No sound was 

 heard when the lamp was unlit, or when it glowed red at a low voltage. 

 When 110 volts was applied to the lamp, a low hissing noise was heard 

 in the telephone, and this gradually died away, after which the ma- 



*Trans. R.S. Canada, p. 115, III, 1914. 



