Absorption of Gas in a Crookes Tube. 509 



end of the anode nearest the glass. The relative amounts 

 of negative glow and positive light in this bulb and in an 

 ordinary cylindrical tube are therefore very different in the 

 two cases, without, as has been shown, influencing the rate 

 at which the tube runs down. 



Fig-. 4. 



ve 



-ve o 



+za<? yiow 



+ve 



In order to compare the results obtained in the last ex- 

 periment with those obtained from previous ones, it was 

 necessary to reduce by calculation the volumes of the appa- 



ratus to the same value in each case, 



>o 



that the 



S<* 



readings may always represent the same mass of gas absorbed. 



The length of the electrodes was also a disadvantage. 



In order to test further the effect of allowing the negative 



glow to develop or of confining it to a small volume, and 

 Fig-. .5. • generally of producing a dissymmetry 



between the two electrodes, a tube like 

 that shown in fig. 5 was used. 



The rate at which the pressure de- 

 creased was determined first when A was 

 cathode, and secondly when the current 

 was reversed. This rate was found to be 

 the same in the two cases, although the 

 appearance of the discharge was very 

 different. 



When A was cathode there was scarcely 

 any positive light to be seen except just 

 on the tip of the anode, and another 

 small plate of it where the tube opened 

 out into a bulb; with A as anode the cylin- 

 drical part was filled with positive light, 

 while the bulb was nearly filled with 

 negative glow. It appears from this that 

 the amount of luminosity developed has 

 no effect on the absorption of the gas. 

 B+ve 6. The tube shown in fig. 5 was silvered 



