

Discharge in a De La Hive's lube. 503 



Then we may reasonably assume 

 n 3 < N 8 , 

 and obviously N = Nj + N 2 — N 3 , 



and n = ni-\-n 2 — n$, 



5. At a high pressure it is reasonable to suppose that 

 Nj > n l9 and we have ( on certain assumptions) experimental 

 evidence for taking N 2 <N 3 [see art. 11]. Therefore, so 

 long as this goes on and we may assume n 2 > n s , we have the 

 number of corpuscles tending to equality with the number 

 of positive ions, the former being greater than the latter 

 initially. The expression (1) is on these suppositions positive 

 at first, and since the expression (4) is always positive the 

 resultant effect is one of mutual repulsion of the various 

 streams, producing a spray discharge. 



6. When w = N, the expression (1) is negative and the 

 total effect will be an attraction when p, the density of the 

 gas, is sufficiently reduced. In this event, the various 

 streams agglomerate and continue as a " band " discharge, 

 so long as the resultant action is an attraction. 



7. When the pressure is further reduced, the number of 

 collisions must become small, but the number of recombi- 

 nations may still be sufficient to neutralize the positive ions 

 produced. In the result, Ave shall have only corpuscles in 

 the tube, and hence the expression (1) will be positive and 

 the resultant action a repulsion, producing a dispersal of the 

 rays [art. 10]. 



It is, of course, well known that at a very low pressure, a 

 discharge-tube contains only corpuscles. This is further 

 verified by the fact that on the creation of a magnetic field, 

 at low pressure, there is an apparent shortening of the 

 positive column. This is best explained by supposing the 

 corpuscles to move in spirals in the magnetic field, as has 

 been shown by J. J. Thomson that they should (art. 52, &c, 

 ' Conduction of Electricity through Gases '). This is also 



partially due to the fact that -^ — ^0 (eqn. 5, art. 8). 



On the whole, then, there will be repulsion between conse- 

 cutive streams, both at the beginning and at the end, and we 

 have thus three stages of the discharge. 



8. II. It is only during the second stage that there is a 

 steady rotation on the application of the magnetic field. 



We have already seen that the variation in the number of 

 corpuscles in the discharge at any moment must depend on 



2L2 ' 



