﻿Velocity of the Cathode-Rays. 359 



ultra-violet light, which possesses in an exaggerated degree 

 the property possessed by the ultra-violet rays of the sun of 

 producing phosphorescence when incident upon such sub- 

 stances as German or uranium glass. It is perhaps worth 

 while to observe, in passing, that the light produced in an 

 ordinary discharge-tube by an intense discharge is very rich 

 in phosphorogenic rays. I have been able to detect phos- 

 phorescence in pieces of ordinary German-g ] ass tubing held 

 at a distance of some feet from the discharge-tube, though in 

 this case the light had to pass through the glass walls of the 

 vacuum-tube and a considerable thickness of air before falling 

 on the phosphorescent body. 



The view, to which Lenard has been led by his experi- 

 ments, that the cathode-rays are setherial waves demands the 

 most careful consideration and attention; for if it is admitted, 

 it follows that the sether must have a structure either in time 

 or space. For these cathode-rays are deflected by a magnet, 

 which, so far as our knowledge extends, does not produce any 

 effect on ultra-violet light unless this is passing through a 

 refracting substance : thus if the cathode-rays are supposed 

 to be ultra-violet light of excessively small wave-length, it 

 follows that in the aether in a magnetic field there must either 

 be some length with which the wave-length of the cathode- 

 rays is comparable, or else some time comparable with the 

 period of vibration of these rays. 



It might be objected that it is possible that the action of a 

 magnet on the cathode-rays is a secondary effect, and that 

 the primary action of the magnet is to affect the main cur- 

 rent of the discharge passing between the positive and negative 

 electrodes, and thus to alter the distribution of the discharge 

 entering the cathode: this would affect the distribution of the 

 places of greatest intensity over the cathode, and thus in- 

 directly the distribution of the waves emerging from it. To 

 test this point I shielded the cathode from magnetic forces by 

 means of a magnetic screen consisting of a ring made of soft 

 iron wire : the length was about 1*5 inch, its thickness was 

 about *75 inch. When this ring encircled the cathode a 

 magnet was brought up to the tube : the phosphorescent 

 patches inside the ring were not now affected by the magnet, 

 but those on the parts of the tube farther away from the 

 cathode and outside the iron ring were very much displaced 

 by the magnet; thus proving that the magnet acts on the 

 cathode-rays through the whole of their course, and does not 

 merely affect the place on the cathode at which they have 

 their origin. There thus seems no escape from the conclusion 

 that the establishment of the hypothesis that the cathode-rays 



