Magnetism on Gases traversed by Electric Discharges. 219 



Pressure under the action of magnetization : — 



Hydrogen. Carbonic acid. Air. 



millims. millims. milliins. 



2-45 3-20 6-72 



2-55 3-30 6-52 



2-80 — 6-50 



Mean . 2*60 3*25 6'58 



The effect was the same also at 40 millims. ; only we could 

 not obtain very regular results with air at that pressure, the 

 discharge therein being too discontinuous. 



Initial pressure of the two gases . . 40 millims. 

 Constant deflection of the galvanometer. 30° 



Pressure under the action of magnetization : — 



Hydrogen. Carbonic acid. 



millims. millims. 



13-54 16-00 



1360 16-24 



Mean . . 13-57 16-12 



From these multiplied experiments we may therefore conclude 

 that the increase of resistance which results for a gas from the 

 action of magnetism is as much greater as the electric conduct- 

 ing-power of the gas is greater. In fact we have seen that it is 

 greatest for hydrogen, the conducting-power of which is very 

 great — less for carbonic acid, which is sensibly less conductive — 

 and least for atmospheric air, which presents a much greater re- 

 sistance than the two preceding gases. As we have already re- 

 marked, the compressibility appears to play only a very secondary 

 part, if any, in this class of phenomena. 



III. Action of Magnetism on the Electric Jet when this is directed 

 along the line which joins the magnetic poles, or Axially. 



The action of magnetism on the electric jet varies, of course, 

 much with the position occupied by the jet relative to the poles 

 of the electromagnet. Divers physicists have occupied them- 

 selves with this subject, and in their researches have considered 

 the most varied cases; but we do not think that the simple case 

 which forms the subject of this section, and, as we shall see, is 

 very interesting, has yet been particularly studied. 



It was necessary that the two ends of the tube through which 

 we transmitted the electric discharge should be capable of being 

 introduced into the cylindrical opening in the two pieces of soft 

 iron of the electromagnet. Therefore the apparatus we used in 

 this series of experiments consisted of a narrow glass tube, 22 



