338 Oil the Discharge of Electricity through Gases. 



field, while they are covered with a glow on removal of magnetisa- 

 tion. 



I have found the following explanation satisfactory in accounting 

 for the phenomena observed by me or recorded by others. Suppose 

 the whole negative electrode to be covered with the glow and then 

 placed into the magnetic field. The negatively charged particles will 

 be deflected in their path, and at some times they will tend to sepa- 

 rate, at others they will be thrown together. Where they are thrown 

 together the temperature will rise, and the discharge will pass more 

 freely, and the current here will be strengthened, and the tempera- 

 ture still further increased. There is then, finally, a tendency of the 

 glow to settle down exclusively at those places at which, owing to the 

 effect of the magnet, the particles are thrown together. If in the 

 vessel (fig. 1) a small electromagnet is introduced into the inner 

 cylinder with its axis at right angles to the axis of the cylinder, it is 

 found that the parts of the aluminium foil covering the two poles of 

 the magnet are absolutely dark (fig. 8, Plate 1). It is clear that, if 

 there was any glow at these parts, the particles carrying the current 

 would be driven asunder, while they are thrown together near the 

 middle parts of the magnet, where consequently the glow becomes 

 strongest. 



If into the same vessel we place a magnet longitudinally, the effect 

 is that observed in fig. 9. Here again the glow settles round the 

 centre of the magnet. The electromagnet used in this last experi- 

 ment had a length of 8 centims., so that it filled completely the 

 aluminium cylinder. That the question here introduced as to the 

 parts of the kathode at which the glow chiefly settles is distinct fronf 

 the more direct effect of the magnet on the glow, once that glow is 

 formed, is clearly shown in cases where the vessel contains two nega- 

 tive electrodes, one of which only is affected by the magnet. I have 

 used, for instance, a vessel containing two aluminium cylinders 

 opposite each other. If a magnet is introduced into one of them, the 

 glow will sometimes be taken away entirely from the other cylinder ; 

 a fact easily explained by the greater facility of the formation of the 

 glow where the temperature is increased by a concentration of 

 particles. 



Fig. 9 also shows a curious effect of the magnet on the width of 

 the dark space. Where the glow is strongest the dark space is very 

 narrow, while it is widened wherever the glow is weak. It has been 

 proved by Crookes that the dark space becomes narrower when the 

 intensity of the current is increased, and the effect shown in the 

 photograph is a simple consequence of this fact. 



I have been during the whole of this investigation very ably assisted 

 by Mr. Arthur Stanton ; without his help I should not have been able 

 to overcome the great practical difficulties which present themselves 



