tipon the Electrical Discharge in Rarefied Gases. 131 



shape, and in some of them with the greatest distinctness. I 

 might say that an entirely new notion is formed of the charactei" 

 of this stratification of the light on seeing, in a tube about 

 2 millims. wide and 400 millims. long, containing traces of 

 hydrogen gas, about 400 clear spaces, alternating with dark 

 intervals, with perfect regularity from one end of the tube to 

 the other, and the dark space which has been before observed 

 occurring only at the warmth-pole (the negative electrode). In 

 wider tubes the dark intervals may attain a breadth of 5 millims. ; 

 they become narrower if the electric light passes from a wider 

 tube into a narrower one. They often appear only after the 

 discharge has passed for a long time through the tube, and then 

 become gradually better and better defined. In most cases the 

 illuminating portions perform small oscillations ; and when this 

 is the case, they give the impression of a spiral motion. They 

 are often, especially towards the negative pole, completely sta- 

 tionary, and appear then as solid immoveable discs. In many 

 cases, especially in wide tubes, these discs assume a strongly 

 conoidal form, the convexity of which is invariably turned to 

 the warmth-pole, thus corresponding to the direction of the 

 electrical discharge. On inverting the poles, the conoidal 

 points, in accordance with the above, assume an opposite di- 

 rection. 



G. It may seem at present premature to attempt to explain 

 fully the stratification of the light produced by the electric dis- 

 charge, for such might perhaps embrace the explanation of the 

 physical process which takes place on such discharge. So much, 

 however, we may already consider as decided, that it is impos- 

 sible for the discharge through Geissler's tubes to consist of the 

 passage of a luminous appearance, or illuminating substance, 

 from one end of the tube to the other ; nor does such an expla- 

 nation derive support from the fact that the discharges of light 

 take place at intervals, which, if Ruhmkorff's apparatus be em- 

 ployed, depend upon the rapidity with which the breakings of 

 the current follow one another. The phtenomcna can only con- 

 sist in an aggregation of matter at definite parts of the tube 

 which become luminous through the discharge, while the pass- 

 age of the electricity from one luminous place to the other is 

 dark. The aggregation of the matter which becomes luminous 

 at these definite places in the tube is a consequence of the dis- 

 charge itself, and often requires a long-continued series of dis- 

 charges. 



7. In the neighbourhood of the warmth-pole, towards which 

 the electricity passes, no aggregation of matter rendered lumi- 

 nous l)y the discharge occurs ; but at this place there is inva- 

 riably a dark space, which in the wider kinds of tubes often 



