508 . Dr. R. S. Willows on the 



heating had slightly increased the rate of absorption. Prob- 

 ably most of the increase of pressure produced by heating was 

 due to water-vapour driven off the walls of the tube. 



4. The previous tube was replaced by one of lead-glass 

 similar to it in all other respects. This ran down at a slower rate 

 (about 10 per cent, less), the gas being air in both cases. The 

 effect for nitrogen was exactly the same as for air in both tubes. 



The lead-glass tube was next filled with hydrogen. Although 

 a strong current was passed for about 35 hours, no decrease 

 in pressure was obtained, but on the contrary it increased, 

 although only very slowly, about one division in several hours, 

 finally. The whole apparatus was pumped down to a very 

 small fraction of a millim., and nitrogen again admitted into 

 reservoir C (fig. 1). By means of taps D, Ea small amount 

 was let into N, and so the tube was filled with nitrogen and 

 the electrodes had had no opportunity of re-absorbing gas. 

 On passing a current the nitrogen disappeared as before. It 

 would seem from this experiment that either hydrogen is not 

 absorbed by lead-glass, or is absorbed so slowly that the small 

 amount of gas ejected from the electrodes, even after long use, 

 is sufficient to overshadow the decrease in pressure resulting 

 therefrom. 



The latter alternative was proved to be the true one. A 

 bulb of lead-glass was filled with hydrogen and an electrode- 

 less discharge passed for some days, the bulb being cut off 

 from the rest of the apparatus, which was made of soda-glass. 

 It was found that the pressure slowly decreased. In a soda- 

 glass bulb the electrodeless discharge caused a much quicker 

 absorption of gas. The fact that absorption takes place with 

 the electrodeless discharge, proves that the gas is not occluded 

 by the metal of the electrodes as is sometimes assumed. The 

 absorption is much slower for the electrodeless discharge 

 than for one in which electrodes are used, but this may be 

 due to the difference in the currents through the gas. 



5. To test whether the distance of the discharge from the 

 glass made any difference, a tube like the one shown in fig. 4 

 was used. Very regular readings could not be obtained with 

 this tube. I attribute this to the difficulty of getting the gas 

 out of the electrodes, the length of the latter rendering this 

 troublesome. 



At the higher pressures (1 mm.) the gas disappeared at 

 a slower rate than w r as the case when a cylindrical tube of 

 smaller diameter was used. At pressures below \5 mm., the 

 shape of the tube made little difference. 



The appearance of the tube at the low pressures was as 

 shown in the figure. The negative glow filled nearly the 

 whole of the bulb, the positive light was only visible at the 



