ON RADIANT MATTER. 21 



gas follows all the convolutions into which skillful glass-blowers can 

 manage to twist the glass. The negative pole being at one end and 

 the positive pole at the other, the luminous phenomena seem to de- 

 pend more on the positive than on the negative at the ordinary exhaus- 



tion 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 of poles, 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 lu- 

 minous phenomena — while the other is exhausted to about the millionth 

 of an atmosphere. I will first connect the moderately exhausted bulb 

 (A) with the induction-coil, and retaining the pole at one side {a) al- 

 ways negative, I will put the positive wire successively to the other 

 poles with which the bulb is furnished. You see that as I change the 

 position of the positive pole, the line of violet light joining the two 

 poles changes, the electric current always choosing the shortest path 

 between the two poles, and moving about the bulb as I alter the posi- 

 tion of the wires. 



This, then, is the kind of phenomenon we get in ordinary exhaus- 



