516 Prof. De la Rive on the Action of Magnetism upon 



led to conclude that the rotation is only apparent, and is the 

 effect of an optical delusion caused by the discontinuity of the 

 discharge. This point is nevertheless worthy of further inves- 

 tigation. 



In order to observe the action of magnetism on the spiral dis- 

 charge, I place the glass spiral between the two poles of the 

 electromagnet, so that its plane is parallel to those of the two 

 polar surfaces, the two prolongations of the spiral being thus 

 vertical, one above and the other below this plane. The mag- 

 netization, according to its direction, either causes a condensa- 

 tion of the discharge against the inside walls of the spiral tube, 

 or, on the other hand, repels it towards the outer walls and 

 makes it very diffuse. In the former case the discharge is very 

 brilliant, and the stratifications are strongly marked; in the second 

 case they are hardly visible, and the discharge itself is much 

 broader and very dull. It seems to undergo, even more distinctly 

 than before, the rotatory motion of which we have already spoken. 

 A rather curious fact is, that in the vertical branch of the tube 

 which is below the spiral, and which is consequently between 

 the two branches of the electromagnet, the discharge divides, 

 under the influence of the magnetism, into two veins, one of 

 which goes to one side of the tube, and the other to the other. 

 One of these veins is very narrow, and of very little brilliance 

 compared with the other. This separation is most likely due to 

 the fact that the induced current of a RuhmkorfPs apparatus 

 consists in reality, as we have already said, of two induced cur- 

 rents successively in opposite directions, one of which has a 

 much greater tension than the other and passes almost alone 

 through the gas, whereas the other is transmitted with great 

 difficulty, but nevertheless passes (though in very small propor- 

 tion, it is true) , since the action of the magnet separates it from 

 the principal discharge, which is in general the only one that 

 we are called upon to consider in phenomena of this kind, in 

 consequence of its much greater strength. 



I endeavoured to determine, in the case of the spiral tube, as 

 I had done with the large straight tube, the influence of mag- 

 netization upon the resistance of the gas to the passage of the 

 discharge; and the result that I obtained was rather curious. 

 The two platinum points of the apparatus for obtaining a de- 

 rived current being immersed in distilled water at a distance of 

 30 millims. from each other, and the spiral tube being filled with 

 hydrogen under a pressure of 2 millims., I obtained a derived 

 current which produced a deflection of 20°. The spiral was 

 placed vertically between the two horizontal armatures of the 

 electromagnet which were exactly in contact with its two faces. 

 As soon as magnetization took place, the derived current was 



