the Electric Discharge in highly Rarefied Gaseous Media, 515 



with the sides of the tube, than when they are placed axially 

 upon the poles themselves. It will be seen that there is a much 

 greater increase of resistance when the magnetism acts on the 

 part of the discharge near the negative electrode, than when it 

 acts on the part near the positive electrode. This difference is 

 caused by the fact that, as was shown in my previous paper, the 

 former part has much the higher conductivity, and therefore 

 naturally undergoes a much greater diminution in conducting- 

 power by the condensation of the gaseous matter caused by the 

 action of the magnet, than it is possible for the second part, 

 where the gas is less rarefied, to undergo. The inversion of the 

 poles of the magnet makes no difference in the foregoing results; 

 its only effect is to cause an elevation or depression of the dis- 

 charge, which is horizontal when the magnet is not in action. 



Among the experiments that I have made upon the influence 

 of the external action of magnetism upon rarefied gases enclosed 

 in tubes, I may still mention some in which the tube was coiled 

 up into a flat spiral terminated by two prolongations, perpendi- 

 cular to the plane of the spiral, which serve for the introduction 

 and rarefaction of the gas, as well as for the passage of the elec- 

 tric discharges. The tube of the spiral, and its prolongations, is 

 a little less than a centimetre in diameter, and its entire length is 

 about 80 centims. With nitrogen or atmospheric air, the rare- 

 faction must be carried at least as far as 2 millims. in order that 

 the discharges may pass ; with hydrogen, the discharge passes 

 when the pressure is reduced to 5 or 6 millims. Moreover, 

 whatever may be the nature of the gas or its degree of rarefac- 

 tion, the discharge does not begin to pass until several minutes 

 after the gas is put into the circuit. It evidently requires to be 

 charged for a long time with statical electricity before the resist- 

 ance to the establishment of a continuous discharge can be over- 

 come. But when once this resistance has been overcome, the 

 passage of the discharge may be interrupted without its being 

 necessary to wait more than an instant before it begins again 

 when the circuit is completed a second time, provided that the in- 

 terruption does not last for more than one or two hours. The 

 luminous discharge through hydrogen under a pressure or 5 or 

 6 millims. exhibits very fine and sharp rose-coloured striae; 

 under a pressure of 2 millims. they become much broader and 

 less sharp, and the colour at the same time becomes paler. The 

 same thing happens with air and nitrogen ; but the effects are 

 most distinct with hydrogen. A remarkable appearance is pre- 

 sented by the discharge in the interior of the spiral ; it seems to 

 possess a very distinct rotatory motion, the direction of which 

 appears to change with the direction of the discharge : this 

 latter result, however, is not very constant ; so that I have been 



