﻿Mr. Norman Campbell on Delta Rays. 63 



do they accord in the least with the evidence derived from 

 the study of curves of the nature given in this and the 

 previous paper. There is no evidence from the relation 

 between current and potential difference of the presence of 

 rays with a speed so high as that corresponding to 25 volts, 

 or of the absence of any rays with a velocity less than 

 28 volts. 



When the amounts of the incident and emergent radiations 

 were under consideration above, a doubt was expressed 

 whether the magnetic field really prevented all the rays 

 from one electrode reaching the other. It is to be noted 

 that if the magnetic field were not everywhere accurately 

 parallel to the plane of the electrodes, but possessed a 

 component perpendicular to them, no increase in the 

 magnitude of the field would produce the condition con- 

 sidered in Thomson's theory. The authors who have been 

 quoted give an account of no investigation designed to test 

 this point, although it is notably hard to obtain a homo- 

 geneous magnetic field over any considerable area. In my 

 own apparatus, many lines of argument showed that the 

 field between the plates was not strictly homogeneous 

 and on this account, as well as on account of the dis- 

 crepancies exhibited by the results of previous workers, an 

 attempt to obtain any quantitative measurements was 

 abandoned. Some observations vvere made, however, on 

 the effect of the magnetic field on the current when 

 different materials were used as electrodes, with the object 

 of detecting any difference in the speed of the rays emitted. 

 The results are not, for the reasons given, very conclusive, 

 but as far as they went they were purely negative. No 

 difference in the effect of the magnetic field could be 

 detected when the material of the electrodes was changed, 

 so long, of course, as both electrodes were of the same 

 material. 



Summary of Results. 



The main portion of the paper is devoted to the destruction 

 of the conclusions given as the result of experiments described 

 in a previous paper under the same title. 



It is concluded that experiments on the relation between 

 the current and the potential difference between the electrodes 

 can give very little information as to the speed of the delta 

 rays emitted from the electrodes. Examination of the form 

 of the curve when the potential difference is small may 

 possibly give a minimum estimate of the speed of the rays ; 

 this minimum estimate, based on the work of other observers. 



