480 Dr. S. Brodetsky and Dr. B. Hodgson on the 



as the pressure decreases, i£ the current is kept constant. 

 The temperatures recorded are the excesses above the 

 temperature of the room. 



Curves B, b in fig. 1 show the results of a similar experi- 

 ment when the temperature of the anode was observed. 

 In A the current strength was "0010 amp., and in B it was 

 •0040 amp. This accounts for the difference in the slopes 

 of the two absorption-curves. In curve b, it will be seen 

 that the anode temperature actually decreased as the 

 absorption increased. The temperature change in the anode 

 was, however, only small, being 6° C. during the expe- 

 riment, whilst with the cathode the temperature change was 

 30° C. for only one quarter the current. 



This indicates that the absorption is more related to the 

 cathode than to the anode. It will be seen later, par. 6, 

 that the particular phenomenon associated with the absorption 

 is the disintegration of the cathode 12 . 



No simple relation could be found between the temperature 

 of the cathode and the rate of absorption. The lag in the 

 reading of the pressure and the temperature made it 

 difficult to approximate closely enough to the actual values. 

 A pressure-gauge that reads without setting would be advisable 

 for this work. 



4. Influence of the Length of the Discharge. — The distance 

 between the electrodes in a vacuum-tube can be increased 

 considerably without altering the conditions at the cathode, 

 if the current strength is kept constant. If the absorption 

 were due to chemical action between the gas and the glass 

 of the tube, then one would expect that the rate of absorption 

 should be greater with a long discharging column than with 

 a short column. One experiment wa's performed with a 

 distance of 35 cm. between the electrodes, and another with 

 a distance of 4 cm. The results are shown in fig. 2. The 

 absorption curves are similar, the shorter column actually 

 absorbing a little faster than the longer one. Unless we 

 are to suppose that, on the basis of the chemical action theory, 

 the action is confined to a limited region of the glow, the 

 results of these experiments seem to militate against the 

 acceptance of this theory. 



5. Absence of Mechanical Absorption by the Electrodes, — 

 In order to discover whether there was any mechanical 

 absorption of gas by the electrodes, experiments were 

 performed in which one electrode consisted of a loop of 

 platinum wire that could be raised to a bright heat by 



12 Tyndall and Hughes, Phil. Mag. xxviii. p. 415 (1914). 



