1879.] on Molecular Physics in High Vacua. 145 



caused by the pliospboresceuce of the residual gas follows all the 

 convolutions and designs into whicli skilful glass-blowers can manage 

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

 positive polo at the other, the luminous phenomena seem to depend 

 more on the positive than on the negative at an ordinary exhaustion 

 such as has hitherto been used to get the best phenomena of vacuum 

 tubes. I have here two bulbs (Fig. 6), 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 stratifications or the ordinary luminous phenomena — whilst the 

 other is exhausted to about the millionth of an atmosphere. I will 



Fig. 5. 



first connect the moderately exhausted bulb with the induction-coil, 

 and, retaining the pole at one side (a) always negative, I will jDut the 

 positive wire successively to the other three poles with which the 

 bulb is furnished. You will see that as I change the position of the 

 positive pole, the line of violet light joining the two poles changes. 

 In this moderately exhausted bulb, therefore, the electric current 

 always chooses the shortest path between the two poles, and moves 

 about the bulb as I alter the position of the wires. 



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

 tions. I will now try the same experiment with a tube that is highly 



