374 Dr. E. Goldstein on the Electric 



when pure dry air was employed. The distance between the 

 similar boundaries of the different layers, or the number of 

 layers in a given distance, is a very delicate test for change of 

 density in the gas. Changes in the residual gas which corre- 

 spond to less than t ^q millim. mercury are shown by very 

 marked changes in the interval between the layers*. 



The current of a coil was first sent through A, the number of 

 layers in the anode-cylinder determined, and the boundary of 

 each on the kathode-side marked on the tube with ink, thus 

 marking the size of each layer. The current was regulated so 

 as to give perfectly steady stratifications. Opening and closing 

 the tap h, before or after turning on the current, did not affect 

 the position of the stratifications. The combination was now 

 brought near to an electromagnet while the current was pass- 

 ing and while the tap h was open, the poles of the magnet 

 being so placed that the discharge appeared compressed 

 towards the side of the tube B furthest from the tube A. If 

 this concentration of the discharge depended upon an increase 

 in density of the gas, then the gas in B outside the column 

 along which the discharge passes must be rarefied, and gas 

 from A would enter and rarefaction in A would result. After 

 a few seconds h was closed, the current of the magnet was 

 interrupted, the tube removed from the neighbourhood of the 

 magnet to guard against the effect of any residual magnetism, 

 and the discharge again sent through A. The number and 

 position of the layers were found to be exactly the same as 

 before the action of the magnet on the discharge. 



The same result was obtained by operating as follows : — 

 The initial density of the stratified discharge of an induction- 

 coil through A was noted; then, after interrupting the current 

 of the coil, the rapidly following discharges of a powerful 

 Holtz machine were sent through B; and this discharge was 

 subjected to the action of the magnet. On now again pass- 

 ing the current of the coil through A, there was no sign of 

 any change in density; any change which had taken place 

 must therefore have been less than y^ millim. mercury; on 

 the other hand, the change of density necessary to produce 

 (when possible) effects upon the discharge, similar to those 

 produced by the action of the magnet at constant density, 

 must be measured by centimetres of mercury. The theory 

 which makes the gas molecules the carriers of the current is 

 therefore in no way supported by experiments with the magnet. 



The view which I take of the part played in the dis- 



* By the interval between two consecutive layers I understand here 

 and elsewhere the distance between the bounding surfaces turned towards 

 the negative pole. 



