1897.] 



on Cathode Bays. 



425 



through a small hole, and the cylinder, when these rays enter it, gets 

 a negative charge, while if the rays are deflected by a magnet, so as 

 to escape the hole, the cylinder remains without charge. It seems 

 to me that to the experiment in this form it might be objected that, 

 though the experiment shows that negatively electrified bodies are 

 projected normally from the cathode, and are deflected by a magnet, it 

 does not show that when the cathode rays are deflected by a magnet 

 the path of the electrified particles coincides with the path of the 

 cathode rays. The supporters of the theory that these rays are waves 



Earth 



Fig. 8. 



in the ether might say, and indeed have said, that while they did not 

 deny that electrified particles might be shot off from the cathode, 

 these particles were, in their opinion, merely accidental accompani- 

 ments of the rays, and were no more to do with the rays than the 

 bullet has with the flash of a rifle. The following modification of 

 Perrin's experiment is not, however, open to this objection: Two 

 co-axial cylinders (Fig. 9), with slits cut in them, the outer cylinder 

 being connected with earth, the inner with the electrometer, are 

 placed in the discharge tube, but in such a position that the cathode 



Fig. 9. 



rays do not fall upon them unless deflected by a magnet ; by means 

 of a magnet, however, we can deflect the cathode rays until they fall 

 on the slit in the cylinder. If under these circumstances the cylinder 

 gets a negative charge when the cathode rays fall on the slit, and 

 remains uncharged unless they do so, we may conclude, I think, the 

 stream of negatively- electrified particles is an invariable accompani- 

 ment of the cathode rays. I will now try the experiment. You 

 notice that when there is no magnetic force, though the rays do not 

 fall on the cylinder, there is a slight deflection of the electrometer, 



