382 Dr. E. Goldstein on the Electric 



passed over by the anode in its approach to the kathode dis- 

 appear one after the other, presenting the appearance of the 

 layers being gradually absorbed by the anode. If the anode 

 is caused to move from its original position away from the 

 kathode, then all the layers originally present remain unaltered, 

 whilst new layers appear in the space left by the anode, of 

 which each immediately upon its formation remains completely 

 indifferent to the further motion of the anode. 



Let us now move the kathode, and first let the motion be 

 an approach to the fixed anode; at once the whole of the 

 layers present begin to move, and are displaced each in the 

 same direction and exactly by the same amount as the kathode 

 itself. (In the distance occupied by the discharge, shortened 

 by the approach of the poles, there is consequently room only 

 for fewer layers than before ; each layer disappears as soon as 

 it is pushed up against the anode by the motion of the kathode.) 

 If the kathode is removed from any initial position whatever 

 further away from the anode, all the layers present follow 

 the kathode, and keep exact time with the motion of the 

 kathode itself; new layers appear in the space between the 

 last of the layers originally present and the anode as the 

 kathode moves further away, and each immediately after its 

 formation follows the motion of the kathode*. 



The interval between every two layers in a cylinder is so 

 little different in passing from one pair to another, that in a 

 cylindrical column of stratified light at given density of gas 

 and intensity of discharge, we may speak simply of the stra- 

 tification-interval of the column. 



The number of layers present is therefore equal to the quo- 

 tient of the length of the column by the stratification-interval. 

 If the distance of the electrodes varies continuously, this 

 quotient will only be a whole number in particular cases. If 

 the division of the space occupied by the discharge into layers 

 advanced from the anode, then in the case when the length 

 of the positive light is not divisible by the stratification-interval 

 without remainder we should expect that the incomplete 

 and abbreviated layer corresponding to this remainder would 

 be found at the negative end of the positive light, whilst at 

 the anode there would be nothing but complete layers. 



Observation shows exactly the contrary: the positive layer 

 nearest the negative end of the positive light, i. e. nearest to 

 the kathode, preserves the same constant extension with every 

 distance of electrodes ; so also the following layers, only the 

 one directly in contact with the anode shortens or lengthens 



* Goldstein, Phil. Mag. [6] iv. p. 362. 



