222 On the Action of Magnetism on electrified Gases. 



produces the rotation (which takes place when the spark strikes 

 between a metallic ring perpendicular to the axis of the magnet 

 and an electrode placed in its centre in the continuation of that 

 axis*), or take place vertically round the axis of a small cylinder 

 of soft iron magnetized by contact with one of the poles of the 

 electromagnet, and of which the extremity constituted one of the 

 electrodes. 



In the first case there is no sensible variation of conductivity 

 in the gas when the jet is put in movement by the action of 

 magnetism ; the conductivity remains exactly what it was when 

 the jet was not under the influence of the magnet and conse- 

 quently was at rest. It is the same when, aqueous or alcoholic 

 vapour being introduced into the rarefied gas, under the mag- 

 netic influence the jet, previously single, is divided into several 

 resembling the spokes of a wheel. 



With aqueous vapour the medium at the same degree of ten- 

 sion is more conductive than the dry gas ; with the vapour of 

 alcohol it is less so, in the same conditions ; but with neither of 

 these two vapours, any more than with the dry gas, does the 

 magnetism, when it determines the rotation of the jet, influence 

 the electric conductivity. 



It is quite different when the jet describes round the rod of 

 magnetized soft iron a cylinder whose axis is that of the rod. In 

 this case there is a very sensible increase of resistance to the elec- 

 tric conduction when the jet, instead of being motionless, rotates 

 from the effect of the magnetism. But this increase is sensibly 

 greater when it is positive electricity that issues from the apex 

 of the soft iron than when it is negative. Thus in the first case 

 we have seen the deflection of the galvanometer diminish from 

 65° to 45°, while in the second case it diminished only from 65° 

 to 55°. Let us remark that in the case in which the diminution 

 of conductivity is the greatest the rotation of the jet seems to 

 be effected with more difficulty, in the same conditions of inten- 

 sity of the electric discharge, intensity of magnetism, and rarefac- 

 tion of the gaseous medium, which is simply atmospheric air at 

 4 millims. pressure : not only is the rotation much less rapid, but 

 the jet itself, instead of remaining vertical, takes during its rota- 

 tion an inclined position ; this is observed to a certain degree in 

 the other case, but is much more pronounced in that in which 

 the conductivity is most diminished. 



It would therefore seem that this diminution of conductivity 

 corresponds- to the constrained position which the electric jet is 

 forced to take under the influence of the magnetizing in the case 

 in which it is naturally vertical ; whereas, when it is naturally 



* In these experiments the magnet was arranged as a vertical column, 

 instead of in a horseshoe-form as in the preceding experiments. 



