Brush Discharge in Water and Salt Solutions. 467 



The bright blue colour of the brush in the first case is evidently 

 due to the amount of continuous spectrum in the blue region 



Fig. 4. 



Wire electrode enclosed in 

 glass tube showing de- 

 cayed point. 



Fig. 6. 



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Brush-discharge : type D. 

 (Separation of bubble from 

 point a little exaggerated.) 



Fig. 5. 



Brush-discharge : Represents 

 types A, B, C, & E, which 

 differ only in extent and 

 colour. 



Fig. 7. 



Brush - discharge : type F. 

 (Enlarged drawing of a 

 photograph.) 



from Hg to H (see PL V. fig. 6, a). In the case of type D, 

 which is produced without a condenser, the stationary 

 bubble mentioned sometimes collapses, and gives place to a 

 stream of much smaller bubbles, the discharge somewhat 

 resembling type E. If this stationary bubble is examined 

 with a low-power microscope, it will be seen that it is- 

 separated from the point by a short space. Occasionally a- 

 fine luminous streamer strikes out from the point across this 

 space, while at odd intervals the space is completely ruptured.. 

 When this occurs, the bubble collapses, and a discharo-e 

 somewhat similar, to type E (Table I.) occurs. Inversion 

 of the electrode does not' cause the bubble to float awav. 

 Consequently the point must hold it in its neighbourhood by 

 electrical action (see fig. 6 in text). 



All the types of capillary discharge tend to become violent 

 with long capillaries. The rotating mirror shows the dis- 

 charge under this condition drawn out into bands of light, 

 each band headed by one or more bright streamers. 



The formation of the stationary bubble which forms at 

 each end of a capillary immersed in a dilute acid or salt 

 solution, is only possible where the capillary is short, not 

 exceeding 2 mm. at most. 



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