

L ^3 j 



Fig-. 1. 



T 



XLIX. Temperature of the Cathode and Anode in a Geissler 

 Tube. By B. Hodgson, M.Sc, Ph.D., Assistant Lecturer 

 in Physics, ± he University, Bristol *. 



§ 1. "VTTHILST working on gas-absorption and cathode 

 T T disintegration in vacuum-tubes, the possibility 

 suggested itself that the temperature of the cathode might 

 play some important part in the phenomena. The following 

 experiments were undertaken to investigate the temperature 

 of the cathode under different conditions of current and gas 

 pressure, other conditions determined by the tube used — as, 

 for example, loss of heat by conduction, &c. — remaining 

 consiant. Their chief interest, however, lies in certain 

 theoretical deductions. 



§ 2. Apparatus. — A high tension 

 battery giving 3200 volts supplied the 

 current. The electrical circuit consisted 

 of this battery, the vacuum-tube, a 

 variable liquid resistance, and a gal- 

 vanometer reading to 10 -6 amp. and 

 shunted for higher currents. A Gaede 

 pump was used for evacuating. The 

 vacuum-tube used was of the form 

 shown in fig. 1. C is the cathode 

 " " shaped to fit closely into the tube T and 

 sealed in position by means of picein. 

 H was a cavity drilled into the cathode 

 and of such a size as to hold the 

 bulb of a thermometer. The tube T 

 just passed inside a larger one D and 

 the whole was made air-tight at D by 

 means of picein. The anode consisted 

 of an aluminium disk E. 



§ 3. The current was kept constant 

 by means of the variable resistance, 

 and the cathode ultimately took up a 

 temperature at which the rate of supply 

 of heat - energy by the bombarding 

 positive ions was equal to the rate of cooling by radiation, 

 conduction, and, to some extent, convection. 



§ 4. Results. — The following tables and curves give the 

 results of some experiments in air, oxygen, and carbon 



* Communicated by the Author. 



