On Radiant Matter. 13 



at the other, the luminous phenomena seem to depend 

 more on the positive than on the negative at the 

 ordinary exhaustion hitherto used to get the best 

 phenomena of vacuum tubes. But at a very high 

 exhaustion the phenomena noticed in ordinary vacuum 

 tubes when the induction spark passes through them an 

 appearance of cloudy luminosity and of stratifications 

 disappear entirely. No cloud or fog whatever is seen in 

 the body of the tube, and with such a vacuum as I am 

 working with in these experiments, the only light observed 

 is that from the phosphorescent surface of the glass. I 

 have here two bulbs (Fig. 7), alike in shape and position 



Fie, 7. 



of pules, the only difference being that one is at an 

 exhaustion equal to a few millimetres of mercury such 

 a moderate exhaustion as will give the ordinary luminous 

 phenomena whilst the other is exhausted to about the 

 millionth of an atmosphere. I will first conned* the mode- 



