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XXVI. On the Action of Magnetism on Gases traversed by Elec- 

 tric Discharges. By MM. A. de la Rive and E. Sarasin*. 



ONE of us (M. de la Rive) has been for a long time occu- 

 pied with the action of magnetism on the electric jets 

 which are propagated in very rarefied gaseous media. In his last 

 researches, which appeared in the Archives des Sciences Physiquesf , 

 M. de la Rive showed that the action of magnetism determines 

 a considerable increase of the resistance to electric cond action — 

 an increase which varies according to the. portion of the jet sub- 

 mitted to the action of the electromagnet, and according to the 

 position of the tube traversed by the discharge relatively to the 

 magnetic poles. 



M. de la Rive has also studied in detail the rotation effects pro- 

 duced by the action of one magnetic pole on the electric jets in 

 various much rarefied gaseous media. He has described the dif- 

 ferences of velocity which result from the greater or less degree 

 of rarefaction of the medium and from its greater or less con- 

 ductivity, dwelling particularly on the curious appearance pre- 

 sented by the electric jet in a medium containing a rather consi- 

 derable proportion of aqueous or alcoholic vapour — which con- 

 sists in the jet being divided into several, forming as it were the 

 spokes of a wheel, and which never takes place at any degree of 

 rarefaction in gaseous media which contain no vapour. 



At the end of his work M. de la Rive intimated that there 

 were still many points in this interesting subject which it was 

 important to elucidate. This is the study which we have under- 

 taken together, and the results of which we now communicate 

 to the Society. 



The first point we had to ascertain was, whether, when an 

 electric jet traverses a rarefied gaseous medium, the influence of 

 the magnetism determines a change of density, probably an in- 

 crease, in the portion of the gas submitted to the action of the 

 magnet. 



We next sought to determine the influence of magnetism on 

 the electric conductivity of the rarefied gases traversed by the 

 discharge when this is effected in a direction perpendicular to 

 the line joining the poles of the electromagnet — that is to say, 

 equatorially. 



Then we studied this influence in a case in which it had not 

 been previously studied, viz. when the discharge is effected axially, 

 or along the line which joins the two poles. 



* Bibliotheque Universelle, Archives des Sciences, May 18/1. Trans- 

 lated from a separate copy communicated by the Authors, having been 

 communicated to the Societe de Physique et d'Histoire Naturelle de 

 Geneve at its meeting on April G, 1871. 



t December 1866, vol. xxvii. p. 289. 



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