514 Prof. De la Rive on the Action of Magnetism, upon 



approach closer together. The action of the magnet produces 

 the same effect as would be caused by a local increase in the 

 density of the rarefied gaseous matter. It is not necessary, 

 however, that the action of the magnet should be exerted exactly 

 upon the dark part in order that it may become luminous ; it 

 becomes so equally even when the magnetism acts upon a dif- 

 ferent part of the discharge, provided that this is not too far 

 removed from the negative electrode. 



A consequence of the explanation that we have just given, 

 which is easily verified experimentally, is that the portion of the 

 gas which transmits the discharge must have a lower conductivity 

 when it is subject to the action of the magnet, and therefore 

 that the electric discharge must encounter a greater total resist- 

 ance in its passage along the inside of the tube, when any part 

 of the tube is brought near the electromagnet, than it did before. 



Thus a tube, 1 metre long, filled with rarefied hydrogen, gave 

 the following results when the apparatus for producing a derived 

 current * was placed in the circuit : — 



Pressure. 



Intensity of the derived current. 





Without 



magnetization. 



Magnetization 



at the posi- 

 tive electrode. 



Magnetization 

 at the nega- 

 tive electrode. 



millims. 

 4 

 3 



33° 

 30 



30° 

 30 



20° 

 10 



With a tube 50 centims. long, filled with rarefied nitrogen, 



the following results were obtained :- 



Pressure. 



Intensity of the derived current. 





Without 

 magnetization. 



Magnetization 



at the posi- 

 tive electrode. 



Magnetization 

 at the nega- 

 tive electrode. 



millims. 

 2 

 4 

 6 



l 



57° 



37 



25 



52° 



27 



20 



42° 



17 



12 



The effects are more marked when the tubes are placed equa- 

 torially between two soft-iron armatures in immediate contact 



* It should not be forgotten that with this apparatus (a description of 

 which is given in my previous paper) the derived current is nearly propor- 

 tional to the principal current; so that its intensity may be taken as being- 

 very approximately a measure of that of the discharge which traverses the 

 tube. 



