1907.] on Ratjs of Positive Electricity. 585 



to accumulate near the cathode, the following experiment was tried to 

 see whether the Kanalstrahlen were produced from traces of hydrogen 

 in the tube. The discharge was sent through the tube in the oppo- 

 site direction, i.e. so that the perforated electrode was the anode, the 

 electric and magnetic fields being kept on. When the discharge 

 passed in this way there was, of course, no luminosity on the screen ; 

 on reversing the coil again, so that the perforated electrode was the 

 cathode, the luminosity flashed out instantly, presenting exactly the 

 same appearance as it had done when the tube had been running for 

 some time with the perforated electrode as cathode. 



The fact that a spot of light produced by the undeflected positive 

 rays is under the action of electric and magnetic forces drawn out 

 into a continuous band was observed by W. Wien, who was the first 

 to measure the deflection of the positive rays under electric and 



mas^netic forces. The values of — obtained from the deflections of 



various parts of this band range continuously from zero, the value 

 corresponding to the undeflected portion, to 10^ the value correspond- 

 ing to those most deflected. Wien explained this by the hypothesis 

 that the charged particles which make up the positive rays act as 

 nuclei, round which molecules of the gas through which the rays pass 

 condense, so that very complex systems made up of a very large 

 number of molecules get mixed up with the particles forming the 

 positive rays, and that it is these heavy and cumbrous systems which 

 give rise to that part of the luminosity which is only slightly deflected. 

 I think that the constancy of the velocity of the rays, indicated by 

 the straight edges of the deflected band, is a strong argument against 

 this explanation, and that the existence of the negative rays is con- 

 clusive against it. These negatively electrified rays, which form the 

 faintly luminous portion of the phosphorescence indicated in Fig. 6, 

 are not cathode rays. The magnitude of their deflection shows that 



the ratio of — for these rays, instead of being as great as 1'7 x 10", 



the value for cathode rays, is less than lO"^. The particles forming 

 these rays are thus comparable in size with those which form the 

 positive rays. The existence of these negatively electrified rays 

 suggests at once an explanation, which I think is the true one, of the 

 continuous band into which the spot of phosphorescence is drawn out 



by the electric and magnetic fields. The values of - which are de- 



m 



termined by this method are really the mean values of — , while the 



m 



particle is in the electric and magnetic fields. If the particles 



are for a part of their course through these fields without charge, 



they will not during this part of their course be deflected, and 



in consequence the deflections observed on the screen, and conse- 



