Absorption of Gases in Vacuum- Tubes, 479 



The results of the experiments to be described in this 

 paper are, on the whole, in agreement with the last ex- 

 planation. 



2. Apparatus and Method. — The apparatus and arrange- 

 ments were similar to those described in Hodgson's paper 

 in the Physikalische Zeitschrift 4 . Glass vacuum-tubes were 

 used, and the current was obtained from a high-tension 

 battery. Gas-pressures were read on a McLeod gauge, and 

 voltages on Braun electrometers. 



3. Mate of Absorption compared ivith Cathode and Anode 

 Temperatures. — It has been shown that the heat-energy 

 given to the cathode is a function of the cathode-fall 10 ' 11 . 

 The following experiment was performed to discover whether 

 any relation existed between the temperature of the cathode 

 (a measure of the cathode-fall) and the rate of absorption of 

 the air in a vacuum-tube. A hollow cathode was used, and 

 in it was inserted the bulb of a thermometer. The current 

 was kept constant, and the gas-pressure, cathode temperature, 

 and the time were observed. Curves A, a (in fig. 1) show 



Fig. 1. 



•4MM. 

 325 



^ 



■ ^ 



JOlh 



■X 



50 



100 



I0O 



200 



150 



300 



200 



4-00 ' 



respectively the pressure-time curve and the temperature- 

 time carve. vlThe curve A is a typical absorption curve for 

 air with copper electrodes. It shows an absorption rate 

 increasing with the time. This means an absorption rate 

 increasing with the cathode- fall, because the latter increases 

 4 See par. 1, note 4. 



°;Hodgson and Mainstone, Phil. Mag. xxvi. p. 411 (1913). 

 ^Hodgson, Phil. Mag. xxvii. p. 189 (1914). 



