Magnetism on Gases traversed by Electric Discharges. 215 



10-12 millims. for carbonic acid, and 15 millims. for hydrogen. 

 A very great number of experiments have shown us that the 

 condensation is the greatest with air, sensibly less with carbonic 

 acid, and very slight with hydrogen. With the medium-sized 

 Ruhmkorff coil, we obtained for the variation of the elastic 

 force, having for the three gases the same initial pressure of 8 

 millims. : — 



Air. Carbonic acid. Hydrogen, 



millim. millim. millim. millim. millim. millim. 

 0-12 and 0-16 0'08 and 0*12 0-02 and 0-04. 



It was needless, as may be seen, to reduce the current to the 

 same intensity in each case, as we had done at first ; for even 

 when this is not done the order in which the gases range them- 

 selves does not change; and the result is then so much the more 

 significant, because the intensity of the current, greater in car- 

 bonic acid and hydrogen than in air, ought on the contrary, if it 

 disturbed the experiments, to invert the order of the three gases. 



Although the numerous experiments made under these condi- 

 tions left no doubt of the effect, variable from one gas to the 

 other, which magnetism exerts on a rarefied medium traversed 

 by the electric discharge, we desired to resume the experiments, 

 and to repeat them with a very powerful Ruhmkorff coil, which 

 permitted us to work with much higher pressures by having a 

 stronger current, and to obtain thereby even much more pro- 

 nounced effects. The following Table contains the results. ob- 

 tained in this new series of experiments : — * 



Differences of Pressure observed. 





Air. 



Carbonic acid. 



Hydrogen. 



millim. 



millim. millim. 



millim. millim. 



millim. 



At 8 



0-10 to 0*12 



0-04 to 006 



002 



15 



0-24 to 0-28 



0-16 



0-04 



20 



0-32 to 0-36 



0-20 



0-06 



These numbers refer to the case in which the compartment 

 containing the negative electrode is placed between the two poles 

 of the magnet, the other being placed outside of its action. Our 

 experiments showed that the effect is much less in the inverse 

 case. When the magnet acted on the positive part of the jet, 

 we obtained for that variation of pressure with air, at 20 millims., 

 0-16-0-18 millim. instead of 0'32 millim. 



It results, then^ from these experiments that the action of 

 magnetism sensibly increases the density of a gaseous medium 

 traversed by the electric discharge in that portion of the medium 



