362 Prof. J. J. Thomson on 



the cathode of which the Oanalstrahlen are the prolongations. 

 The first place in which they were found is right in front of 

 the cathode. The discharge-tube is represented in fig. 2. 

 A perforated plug was placed at the entrance of the tube A, 



Fig-. 2. 



-*H> 



i 



and at the end of this tube there was a willemite screen B ; 

 the tube passed between the poles of a powerful electro- 

 magnet of the Du Bois type and contained two parallel plates, 

 which when connected with a large battery of small storage- 

 cells had a strong electric field between them. When k was 

 cathode, the tube was flooded with ordinary cathode rays, 

 but these could easily be turned to one side by a small per- 

 manent magnet : when this was done there still remained a 

 bundle of rays passing through the aperture which were not 

 appreciably deflected by the weak magnetic field, but which 

 suffered appreciable deflexion by strong magnetic and electric 

 fields. The direction of the deflexion showed that they con- 

 sisted of positively charged particles ; the magnitudes of the 

 deflexions were comparable with those of the rays which pass 

 through apertures in the cathode ; but even rough measure- 

 ments were sufficient to show that the velocity of these 

 particles in front of the cathode was less than that of the par- 

 ticles which had traversed the cathode. Viliard (Comjptes 

 Rendus, vol. vii. p. 674) has described a similar experiment 

 and obtained the same results. The luminosity produced on 

 the screen in this experiment, though quite appreciable, 

 was much less than that produced by the ordinary Canal- 

 strahlen, and was rather too faint to allow of very accurate 

 measurements of e/m and v. I have deferred making 

 these measurements in the hope of improving the appa- 

 ratus so as to get much brighter phosphorescence. Along 

 with the rays which were positively deflected, there were 

 others which were not deflected by the strongest fields I could 

 apply; and, as in the case of the rays coming through the 

 cathode, there were some rays which were deflected in the 

 negative direction, and which consisted of particles having a 

 negative charge and a mass much greater than that of a 

 corpuscle. The existence of the positive rays in front of the 

 cathode and travelling away from it, might be explained by a 

 kind of reflexion of those travelling towards the cathode: we 

 might suppose that some of these, when close to the cathode, 



