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



do not find it any easier to pass along this line in consequence 

 of the passage of the previous one. There will not. therefore, 

 be the same instability in this case as in the one where no 

 magnetic force acted upon the gas. A confirmation of this 

 view is, I think, afforded by the appearance presented by the 

 discharge when the intensity of the magnetic field is reduced, 

 so that the discharge just, but only just, passes when the 

 magnetic field is on. In this case the discharge, instead of 

 passing as a steady fixed ring, flickers about the tube in a very 

 undecided way. 



If the strength of the magnetic field is reduced still further, 

 so that the discharge passes with some ease, the bright ring 

 which, when no magnetic force is acting, is in one plane, is 

 changed into a luminous band situated between two planes 

 which intersect along a diameter of the bulb at right angles 

 to the magnetic force. These planes are inclined at a con- 

 siderable angle, one being above and the other below the 

 plane of the undisturbed ring. This displacement of the ring 

 by the magnetic force shows that it consists of currents cir- 

 culating tangentially round the ring. 



This action of a magnet on a discharge flowing at right 

 angles to its lines of force is not, however, the only remarkable 

 effect- produced by a magnet on the discharge. When the 

 lines of magnetic force are along the line of discharge, the 

 action of the magnet is to facilitate the discharge and not to 

 retard it as in the former case. The first indication of this 

 was observed when the jars were connected, as in (a) in fig. 1. 

 The earth-connexion being removed, in this case there is a 

 glow from the glass into the bulb, due to the redistribution of 

 the electricity induced on the glass by the primary when it is 

 at a high potential before the spark passes. If the primary 

 is connected to earth by a circuit with an air-break in it, the 

 intensity of the glow may be altered at will by adjusting the 

 length of the air-break ; when the air-space is very small 

 there is no glow ; when it is long the glow is bright. The 

 bulb in which the discharge was to take place was placed on 

 a piece of ebonite over the pole of an electromagnet, and the 

 air-space in the earth-connexion of the primary was adjusted 

 so that when the magnet was off no glow was observed in the 

 tube. When the magnet was on, however, a glow radiating in 

 the direction of the lines of magnetic force was produced, 

 which lasted as long as the magnet was on, and died away 

 rapidly, but not instantaneously, when the magnet was taken 

 off. In this case the discharge seems to be much easier along 

 the lines of magnetic force. 



The following experiment shows that this effect is not 



