216 MM. A. de la Rive and E. Sarasin on the Action of 



on which the action is exerted. This effect varies according to 

 the different gases : it is so much the greater as the electric eon- 

 dueting-power of the gas is less. It varies also according to the 

 portion of the jet submitted to the action of the magnet, being 

 a maximum when the magnet acts on the negative portion. 



We confine ourselves for the present to stating the fact, with- 

 out venturing as yet to give the interpretation of it. It may 

 proceed either from a real condensation of the gaseous molecules 

 effected by the magnetism, or from a difference of temperature 

 between the part of the jet which is submitted to the magnetic 

 action and that which is not, or from both causes combined. 

 We purpose to resume the examination of this question in the 

 study which we intend to make of the influence of magnetism 

 on the calorific effects produced by the passage of the electric 

 discharge through rarefied gases. 



II. Action of Magnetism on the Conductivity of Rarefied Gases 

 when the Electric Discharge is directed transversely to the line 

 which joins the poles of the electromagnet, or Equatorially. 



In order to study the influence of magnetism on the resistance 

 opposed by a rarefied gas to the transmission of the electric dis- 

 charge when this takes place in a direction perpendicular to the 

 line of the poles of the electromagnet, we used a cylindrical glass 

 tube of which the dimensions were such that the electric jet was 

 submitted in its whole length to the intense action of the mag- 

 netism. This tube was 20 centims. long, and 35 millims. in 

 diameter; at each extremity it had a brass mounting with a 

 stopcock and a knobbed electrode, also of brass. The distance 

 between the two electrodes was equal to the diameter of the soft 

 iron of the electromagnet, viz. 9 centims. This cylinder was 

 arranged like the large tube with glass stopcock in the preceding 

 experiment, and communicated by lead pipes, at one end with 

 the manometer, and at the other with the air-pump. 



That we might be able to institute a comparison between the 

 three gases on which we wished to operate, it was necessary to 

 reduce them all to the same pressure, and pass through them a 

 current of the same intensity. But as it was not easy to place 

 a rheostat in the induced circuit, we thought of varying the in- 

 tensity of the inducing current by introducing a wire of German 

 silver of greater or less length. The induced current traversing 

 the rarefied gas was measured by means of a very sensitive gal- 

 vanometer* and the apparatus described by M. de la Rive in his 

 researches on the electric discharge in rarefied gases f. Lastly, 



* This galvanometer was placed in an adjoining room, at a sufficient dis- 

 tance from the electromagnet to preclude its needle being influenced by it. 

 f Archives des Sciences Phys. et Nat. July 1860, vol. xxvi. p. 177- 



