94 Prof. Chattock, Miss Walker, and Mr. Dixon on the 



As the current is reduced the effect of accidental errors 

 should become increasingly important, the dotted line tending 

 towards A A. This is well shown in the figures. In the case 

 of the highest negative discharges in hydrogen the dotted line 



Fig. 8.— Hydrogen. w=19. B. III. 



Negative. 



P) 14 



< 





/B 





13 





k 



// 

 It 







J 







12 





J 





A 











11 Pi 



Microamps 3-2 



has actually crossed BB, which is not in accordance with 

 theory. If this is due to more than an accident, it may be 

 explained by supposing that the more rapidly moving ions 

 give rise to greater back-discharge than the slower ones, 

 which seems reasonable enough. 



If the conclusions arrived at above are to be accepted, we 

 have, in considering the case o£ hydrogen, to reconcile 

 variations of something like 100 per cent, between the extreme 

 values of V— with practical constancy in the value of V+. 

 The only obvious changes in the conditions of discharge were 

 those of temperature, pressure, and purity of the gas, which 

 must have been extremely small in our experiments ; and it 

 seems hardly possible that they should be responsible for such 

 large effects. 



A solution of the difficulty is perhaps to be found in the 

 fact that the negative discharge from a point is apparently 

 much more closely dependent upon the condition of the point 

 surface than the positive. 



It is an instance of this that a needle-point which when 

 discharging positive electricity is covered with a smooth 

 velvety glow, often discharges negative from a single 

 spot on its surface, the position of which will move irregu- 

 larly and suddenly in a manner suggestive of local surface 

 changes. 



The frequent and large fluctuations in the strength of the 

 field close to a point discharging negative electricity — changes 



