Discharge in Rarefied Gc 



385 



for the simple cylinder, but the colours of the layers between 

 x and A show no regular relationship to their position in order 

 from K; their colours remain the same however their position 

 in order varies. But if x be moved, the same law holds good 

 for these layers as if x were a metallic kathode — the colour of 

 each depending on its position in order from x, and the colour 

 of every nth layer, counting from x, remaining the same for 

 every position of x. 



The dependence of the stratifications upon their secondary 

 negative pole, and the complete analogy with the dependence 

 upon the metallic kathode, is seen, lastly, also in the influence 

 of the magnitude of the secondary pole. If its magnitude be 

 diminished the layers become further apart, as if from a dimi- 

 nished metallic kathode ; and the displacement is in both 

 cases more marked when the surface of the pole is diminished 

 in a greater ratio*. 



If we have now a tube (fig. 5) provided with 

 two secondary poles x and y of this kind, of which 

 only x is movable and y is fixed (the piece W of 

 which y is the mouth may be conveniently united 

 with the wall of the large vessel by fusion when 



* The diminution of a secondary negative pole- may 

 be effected in a variety of ways. Fig. 6 shows in one 

 diagram three different simple arrangements for effecting 

 this: — 



In cylinder I. a glass diaphragm is arranged perforated 

 with two round openings of different sizes ; a glass ball is 

 also enclosed in the tube, whose diameter exceeds that of 

 the largest opening. By allowing the glass ball to rest 

 upon the one or the other of the two openings, the dis- 

 charge issues from a larger or smaller secondary pole. 

 (Of course the opening acts on the side towards the ka- 

 thode as a secondary positive pole.) 



In cylinder II. the opening x of the communicating 

 glass tube is the secondary negative pole ; a glass rod, 

 provided at one end with a knob to prevent its falling 

 completely through, is movable to and fro in r. It is 

 clear that by this means the magnitude of the opening x 

 may be varied. 



Cylinder III. shows the simplest arrangement, a glass 

 tap the perforation of which replaces the communicating 

 tube. The magnitude of the secondary pole is a maxi- 

 mum when the tap is completely open. If we gradually 

 turn the tap from this position, and so gradually reduce 

 the magnitude of the secondary negative pole, we see 

 the layers gradually recede from the pole. The advan- 

 tage of this arrangement is found in the power of gradu- 

 ally altering the magnitude of the pole ; its disadvantage 

 in the gradual alteration of the quantity of gas contained 

 in the tube, by the evolution of gases produced by the 

 action of the discharge on the substance with which the tap is lubricated 



