334 Prof. J. J. Thomson on the Discharge of Electricity 



the main one ; the action of the magnetic force on the chain 

 of polarized molecules which are formed before the discharge 

 passes might produce an effect equivalent to that which we 

 have supposed was produced on an actual discharge. 



The chain of polarized molecules would he affected in the 

 following way : — The magnetic field due to the electromagnet 

 consists of tubes of electrostatic induction moving about ; 

 these tubes, as well as the direction in which they are moving, 

 are at right angles to the lines of magnetic force. The short 

 tubes of electrostatic induction which join the atoms in the 

 molecules of the gas will, under the influence of the electric 

 forces, set themselves parallel to the direction of the electro- 

 motive intensity at each point. 



Thus, when the magnetic force is at right angles to the 

 line of discharge, tubes of electrostatic induction parallel to 

 those in the molecules will be moving about in the field ; and 

 since parallel tubes exert attraction and repulsion on each 

 other, the molecular tubes will be knocked about and their 

 efforts to form closed chains made much more difficult by 

 the action of the magnet. On the other hand, when, the lines 

 of magnetic force are parallel to the discharge, the moving 

 tubes are at right angles to those in the molecules, and will 

 not disturb them in the attempt to form chains along the line 

 of magnetic force, they will in fact assist them in doing so by 

 preventing all attempts in directions across the lines of force. 



Prof. G. F. Fitzgerald has suggested to me in conversation 

 that this action of a magnet on the discharge might be the 

 cause of the " streamers " which are observed in the aurora; 

 the rare air being electrically weaker along the lines of mag- 

 netic force than at right angles to them will cause the 

 discharge in the direction of those lines to be the brightest. 



Discharge through different Gases. 



I have examined the discharge through air, carbonic 

 acid, hydrogen, oxygen, coal-gas, and acetylene. As I have 

 already mentioned, at the highest pressures at which the 

 discharge passes through air, the discharge is reddish, and 

 gets brighter and whiter at lower pressures. If the discharge 

 is examined through a spectroscope, the lines in the spectrum 

 coincide with those obtained by sparking through air in the 

 ordinary way with a jar in the circuit. The relative bright- 

 ness of the lines in the spectrum of the discharge without 

 electrodes varies very much with the pressure of the gas and 

 the length of spark in the jar circuit. With a long spark in 

 this circuit, and the pressure such as to give a bright white 



