the Electric Discharge in highly Rarefied Gaseous Media. 513 



coming perpendicular to that of an element when the latter is a 

 tangent to the magnetic curve. 



On the present occasion, my object is to investigate with 

 greater detail the influence exerted by magnetism on electricity 

 when traversing rarefied gases. My researches comprise two 

 series of experiments : — first, those in which the electromagnet, 

 which is the source of the magnetic action, is placed outside the 

 rarefied gas through which the electric discharge passes ; and 

 secondly, those in which the magnetized soft iron is situated 

 within the gas itself. 



§ 1. Experiments in which the electromagnet is placed outside 

 the rarefied gas. 



One of the simplest cases is when a glass tube containing the 

 rarefied gas through which the electric discharges are passing is 

 placed either axially or equatorially with regard to the poles of 

 a strong electromagnet. When care has been taken to rarefy 

 highly the gas which transmits the electric discharge, the follow- 

 ing appearances present themselves : — The portions of the dis- 

 charge subject to the magnetic action are squeezed up against 

 the sides of the tube at the parts nearest or furthest from the 

 poles of the magnet, according to the direction of the discharge 

 and the position of the poles ; the strise at the same time become 

 much narrower and more brilliant. If the part of the tube near the 

 electromagnet is that containing the negative electrode, the dark 

 space immediately becomes luminous and presents narrow bright 

 striae, just as the constantly luminous part of the discharge, 

 which seems to advance, would do. At the same time the 

 bluish photosphere surrounding the negative knob diminishes 

 in thickness by at least one-half and becomes more brilliant, and 

 the sort of bluish sheath which surrounded the metallic stem 

 at whose extremity the negative electrode is placed, disappears 

 entirely. The whole of this bluish atmosphere becomes con- 

 centrated about the knob. It seems that all the gaseous veins, 

 which may be regarded as so many conductors of the discharge, 

 instead of radiating from all points of the negative knob and 

 stem' and spreading out through the whole gaseous mass as far 

 as the positive electrode, when the magnetic action is exerted 

 upon them radiate only from the negative knob and are con- 

 densed against either one side of the tube or the other, until they 

 arrive at that part of their course where the action becomes in- 

 sensible and they accordingly resume their normal position. 

 This condensation explains why the part of the discharge which 

 was dark, because the gas was there so greatly rarefied, becomes 

 luminous, and why the part which was already luminous becomes 

 narrower and more brilliant, while the strise which it exhibits 



