294 Frof. J. J. Thomson on Cathode Bays. 



unobserved phenomena in the sether, of whose laws we are 

 ignorant. 



The following experiments were made to test some of the 

 consequences of the electrified-particle theory. 



Charge carried by the Cathode Rays. 



If these rays are negatively electrified particles, then when 

 they enter an enclosure they ought to carry into it a charge 

 of negative electricity. This has been proved to be the case 

 by Perrin, who placed in front of a plane cathode two coaxial 

 metallic cylinders which were insulated from each other : the 

 outer of these cylinders was connected with the earth, the 

 inner with a gold-leaf electroscope. These cylinders were 

 closed except for two small holes, one in each cylinder, placed 

 so that the cathode rays could pass through them into the 

 inside of the inner cylinder. Perrin found that when the rays 

 passed into the inner cylinder the electroscope received a 

 charge of negative electricity, while no charge went to tho 

 electroscope when the rays were deflected by a magnet so 

 as no longer to pass through the hole. 



This experiment proves that something charged with nega- 

 tive electricity is shot off from the cathode, travelling at right 

 angles to it, and that this something is deflected by a magnet; 

 it is open, however, to the objection that it does not prove 

 that the cause of the electrification in the electroscope has 

 anything to do with the cathode rays. Now the supporters 

 of the setherial theory do not deny that electrified particles 

 are shot off from the cathode ; they deny, however, that these 

 charged particles have any more to do with the cathode rays 

 than a rifle-ball has with the flash when a rifle is fired. I have 

 therefore repeated Perrin's experiment in a form which is not 

 open to this objection. The arrangement used was as follows: — 

 Two coaxial cylinders (fig. 1) with slits in them are placed 

 in a bulb connected with the discharge-tube ; the cathode rays 

 from the cathode A pass into the bulb through a slit in a metal 

 plug fitted into the neck of the tube ; this plug is connected 

 with the anode and is put to earth. The cathode rays thus do 

 not fall upon the cylinders unless they are deflected by a 

 magnet. The outer cylinder is connected with the earth, the 

 inner with the electrometer. When the cathode rays (whose 

 path was traced by the phosphorescence on the glass) did not 

 fall on the slit, the electrical charge sent to the electrometer 

 when the induction-coil producing the rays was set in action 

 was small and irregular; when, however, the rays were bent 

 by a magnet so as to fall on the slit there was a large charge 

 of negative electricity sent to the electrometer. I was sur- 

 prised at the magnitude of the charge ; on some occasions 



