220 



Mr Monchnan, Discharge in Vacuo 



[Nov. 9, 



25 mm. beyond which the current always took one path and could 

 not be changed. 



Fig. 2. 



With this jar reversals were obtained not only when the 

 current was reversed, but also on restarting after a short break. 

 The latter appeared to be caused by an agency about half as 

 energetic as the former. 



After allowing air to enter the receiver and again exhausting, 

 the force that previously acted was found to have decreased, and 

 the next discharge might or might not take the same path as the 

 last before admitting the air. 



When using a powerful Wimshurst machine, in a dark room, 

 during the performance of an experiment to be described later, I 

 observed that when the knobs were opened beyond the position of 

 taking an ordinary spark, there began to be a glow around the 

 negative which illuminated a somewhat globular space around 

 that pole. The positive spark passed into this space, but con- 

 stantly changed its course, sweeping the negative charge away 

 from its path, it then took another path and having cleared that 

 of negative changed again and so on through a kind of cycle. 



If there were two paths open as Fig. 2 and a spark passed 

 from C to A, removing part of the glow from the space around A, 

 there would (after cooling) be a greater tendency for the next 

 spark to pass between D and B. 



On the other hand if after a spark had passed between G and 

 A the direction of the spark were reversed, it would most probably 

 pass from B to D, there being a larger quantity of negative around 

 D than around A. 



This is probably the explanation of the previous reversals and 

 also why the introduction of air into the receiver decreased the 

 power of producing it. 



Underlying the whole matter is the cause of the production of 

 the glow at the negative and why some gases produce it better 



