Absorption of Gases in Vacuum- Tubes. 483 



cathode-fall increased, as is shown in fig. 3. The numbers 

 on the curves give the cathode-fall in volts. The curves are 

 typical of air and oxygen with copper electrodes. They can 

 be divided into two parts, one with a small absorption rate, 



Fig. 3. 



AIR *TK 



/>006 



I l, 



0-6 



C-7JMP/:, 



0-5 



+-^00 



+V700 



0-0- 



C-5 



OXYGEN 



'*■>?-*-*. 



00 



900 0-3 



CM 



<->4 c 



60oH^oc\ l(4)C 



0£ 



0-3 



SDO^ -h!300 



800 A I 0-> 



0-2 



1300* 



I MiNUTES 

 4-0 60 60 FOG !20 !^0 160 180 



and the other with a greatly increased and accelerated rate 

 when the cathode-fall has reached a certain value. Exactly 

 similar results were obtained in fourteen experiments in air, 

 and five in oxygen. 



The explanation of the general form of these curves is not 

 far to seek. It is to be found in the formula given by Stark 

 connecting the cathode-fall with the pressure 13 . Stark's 

 formula can be written 



Y=k(C-! P )i/p, 



(1) 



C being the current strength, p the pressure, and V the 

 difference between the actual cathode-fail in the abnormal 

 state and the normal cathode-fall, which latter is constant; 

 k and I are constants depending upon the circumstances of 

 the experiment and the dimensions of the tube. The 

 temperature was tolerably constant in the experiments here 

 discussed, as the cathodes used were fairly large. 



13 Stark, Phys* Zeit. iii. p. 274 (1902). 



2 K2 



