Theory of the- Striated Discharge, 991 



where L = fE f(^)\ .... . (19) 



M=i7i*{£/<w»}* (20) 



The distribution of X the electric force along the tube is 

 represented by the lower curve in fig. 1. The electric force 

 is a maximum at the places C, O b C 2 , the points on the 

 cathode side where the line E = Ei cuts the graph for E ; 

 it is a minimum at the points C\ (V, C/, the points on 

 the anode side where the same line cuts the graph. The 

 graph shows that the electrification in the tube is positive 

 between C and C, d and Or, C 2 and 2 ', negative at 

 other parts of the tube ; the positive electrification is 

 greatest at the maximum values of E, the negative at the 

 minimum values. The electric force may change sign ; 

 it will be in the normal direction, i. e. the direction indi- 

 cated by the potential difference between the anode and 

 cathode, on the ascending parts of the giaph for E, but may 

 be in the opposite direction in the descending portions. I 

 have observed (Phil. Mag. xviii. p. 441, 1910) this reversal 

 of the sign of the electric force in the striated discharge. It 

 must be remembered that these results have been obtained on 

 the assumption that the pressure is so low that we can in 

 the equation for E neglect the terms in d^jdx in com- 

 parison with d 2 l&\dx 2 . If we take the other extreme when 

 the pressure is so high that we can neglect d"~Ej/da 2 in 

 comparison with dE/dx, we find that the graph for E is 

 like that represented in fig. 2. In this, E does not fluctuate 



Fier. 2. 



but approaches as an asymptote the line E = Ei ; the graph 

 for X takes a similar course and there are no alterations 

 in sign ; the electrification is everywhere negative, but 

 diminishes in intensity towards the anode. This type of 

 discharge would show a uniform positive column but no 

 striations. 



