428 Professor J. J. Thomson [April 30, 



electrostatic action of the cathode rays ; this force penetrates the 

 cylinder and produces a discharge of electricity from the far side 

 of the brass. 



Another efifect which I believe is due to the negative electrifica- 

 tion carried by the rays is the following. In a very highly exhausted 

 tube provided with a metal plug, I have sometimes observed, after 

 the coil has been turned off, bright patches on the glass ; these are 

 deflected by a magnet, and seem to be caused by the plug getting 

 such a large negative charge that the negative electricity continues to 

 stream from it after the coil is stopped. 



An objection sometimes urged against the view that these cathode 

 rays consist of charged particles, is that they are not deflected by an 

 electrostatic force. If, for example, we make, as Hertz did, the rays 

 pass between plates connected with a battery, so that an electrostatic 

 force acts between these plates, the cathode ray is able to traverse 

 this space without being deflected one way or the other. "We must 

 remember, however, that the cathode rays, when they pass through a 

 gas make it a conductor, so that the gas acting like a conductor 

 screens off the electric force from the charged particle, and when the 

 plates are immersed in the gas, and a definite potential difference 

 established between the plates, the conductivity of the gas close to 

 the cathode rays is probably enormously greater than the average 

 conductivity of the gas between the plates, and the potential gradient 

 on the cathode rays is therefore very small compared with the average 

 potential gradient. We can, however, produce electrostatic results if 

 we put the conductors which are to deflect the rays in the dark space 

 next the cathode. I have here a tube in which, inside the dark space 

 next the cathode, two conductors are inserted ; the cathode rays start 

 from the cathode and have to pass between these conductors ; if, 

 now, I connect one of these conductors to earth there is a decided 

 deflection of the cathode rays, while if I connect the other electrode 

 to earth there is a deflection in the opposite direction. I ascribe this 

 deflection to the gas in the dark space either not being a conductor 

 at all, or if a conductor, a poor one compared to the gas in the 

 main body of the tube. 



Goldstein has shown that if a tube is furnished with two cathodes, 

 when the rays from one cathode pass near the other they are repelled 

 from it. This is just what would happen if the dark space round the 

 electrode were an insulator, and so able to transmit electrostatic 

 attractions or repulsions. To show that the gas in the dark space 

 differs in its properties from the rest of the gas, I will try the follow- 

 ing experiment. I have here two spherical bulbs connected together 

 by a glass tube ; one of these bulbs is small, the other large ; they 

 each contain a cathode, and the pressure of the gas is such that the 

 dark space round the cathode in the small bulb completely fills the 

 bulb, while that round the one in the larger bulb does not extend 

 to the walls of the bulb. The two bulbs are wound with wire, which 

 connects the outsides of two Ley den jars ; the insides of these jars 



