422 



Professor J. J. Thomson 



[April 30, 



a magnet. Again, if the discharge, instead of taking place between 

 points, passes between flat discs, the effect of the magnetic force is to 

 move the sparks as a whole, the sparks keeping straight until their 

 terminations reach the edges of the discs. The fine thread-like 

 discharge is not much spread out by the action of the magnetic field. 

 The appearance of the discharge indicates that when the discharge 

 passes through the gas it manufactures out of the gas something 

 stretching from terminal to terminal, which, unlike a gas, is capable of 

 sustaining a tension. The amount of deflection produced, other circum- 

 stances being the same, depends on the nature of the gas ; as the photo- 

 graphs (Figs. 3 and 4) show, the deflection is very small in the case 

 of hydrogen, and very considerable in the case of carbonic acid ; as a 

 general rule it seems smaller in elementary than in compound gases. 



Fig. 5.— Hydrogen (Ammeter, 12 ; Vultmeter, 1600). 



Let us contrast the behaviour of this kind of discharge under the 

 action of a magnetic field with that of the cathode rays. I have here 

 some photographs (Figs 5, 6 and 7) taken of a narrow beam formed 

 by sending the cathode rays through a tube in which there was a 

 plug with a slit in it, the plug being used as an anode and connected 

 with the earth, these rays traversing a uniform magnetic field. The 

 narrow beam spreads out under the action of the magnetic force into 

 a broad fan-shaped luminosity in the gas. The luminosity in this 

 fan is not uniformly distributed, but is condensed along certain lines. 

 The phosphorescence produced when the rays reach the glass is also 

 not uniformly distributed ; it is much spread out, showing that the 

 beam consists of rays which are not all deflected to the same extent 



