Vacua, and on Coronoidal discharges. 467 



■charge would start this time was smaller than in the first case 

 and the smaller the shorter the interval between the time of 

 taking the bulbs out and immersing them again. This differ- 

 ence is, of course, due to the improved conductivity of the 

 gas and this again may in a certain measure be due to the rise 

 in temperature of the gas on account of the heating effect of 

 the discharge ; but only in a small measure, for the bulbs were 

 under water, so that the rise in temperature must have been 

 very small. Besides, heating the bulbs with a Bunsen burner 

 before immersion did not diminish the depth at which the dis- 

 charge would start nearly as much as a previous discharge 

 would, no matter of how short a duration. As stated above, 

 the discharge may be started far below the critical point by 

 touching the connecting tube. But if the touch, lasts only a 

 very short time (a fraction of a second) the discharge ceases as 

 soon as the touching conductor leaves the tube. In this man- 

 ner the vacuum tube may be made to blaze up in quick suc- 

 cessions. 



This behavior of the discharge at all pressures, but very 

 much more striking at pressures higher than the pressure under 

 consideration, seems to support the dissociation theory of 

 Prof. J. J. Thomson (Phil. Mag. 1891, vol. xxxii, pp. 329, 

 454, 455). 



II. PHENOMENA INDICATING A DISSOCIATION OF THE MOLECULES. 



The following phenomenon appears to be an additional sup- 

 port of this theory : 



A close inspection of the discharge going on in the bulbs A 

 and B, fig. 8, seemed to reveal the strange fact that the elec- 

 trical flow was confined to a thin layer of the rarified gas 

 which is in immediate contact with the inside surface of the 

 bulbs, especially when the e. m. f. was not too far above the 

 critical point and therefore the supply of the current not too 

 plentiful. To all appearances there was a gliding film of 

 luminous gas in each bulb extending from the mouths of the 

 connecting tube, spreading over the inside surfaces and ending 

 at the bottom of the bulbs in. violently agitated luminous 

 clouds which gave the discharge a hazy appearance. When 

 the vacuum was very good both the film and the clouds were 

 absent. There was no suggestion of a motion on the part of 

 the gas, and the discharge had a clear luminosity. To study 

 this phenomenon more closely the following experiment was 

 performed : 



A glass bulb «, fig. 9, blown out at one end of a thick glass 

 tube of narrow bore was filled with acidulated water and 



