﻿02 Mr. Norman Campbell on Delta Rays. 



Further limitations must also be noticed. Since we have 

 concluded that an increase in the electric field between the 

 electrodes may change the current by increasing the number 

 w T hich are dragged out of the electrode, it is clear that the 

 method by which the magnetic field is kept constant and 

 the electric field is varied is illegitimate. This method was 

 employed by Ewers*. On the other hand, it is obvious 

 that no rays must be emitted from any part of the apparatus 

 except the parallel plates, or at least from none whence the 

 rays can reach the electrodes by travelling along (and not 

 across) the magnetic field ; for if there are such rays they 

 will not be affected to the same extent by the magnetic 

 field. Now in Hauser's experiment one electrode is com- 

 pletely surrounded by the other and delta rays are excited 

 from all parts of both electrodes which the alpha rays can 

 reach ; accordingly Hauser's results must also be viewed 

 with considerable suspicion. 



If, notwithstanding these objections, we calculate the 

 values of v and e/m given by the experiments of these 

 authors, we obtain the following results : — 



Ewers : d=l'7 ; H = 20 ; X 2 = 79 x 10 8 ; X^O, 



and r = 2'0 x 18 8 ; ejm = l-16 x 10 7 . 



Hansen d = 0'0S ; X = 122xl0 8 ; H 1= :5G; EL = 000, 



and v = 2'2 X 10 8 ; e/m = l'0 X 10 7 . 



It will be observed that there is considerable agreement 

 between the results, but that the value deduced for e/m is 

 much smaller than the 1*77 x 10 7 which is now accepted. 



Owing to the objection which has been raised as to the 

 heterogeneity of the rays, it is perhaps more satisfactory to 

 assume the value for e/m, and then to calculate the maximum 

 and minimum values of v given by the two conditions. In 

 this way we obtain : — 



Ewers : v (max.) =3'0 x 10 8 corresponding to 25*5 volts, 

 u(min.)=l-0xl0 8 „ „ 2-8 „ 



Hauser: v (max.) =4'0 X 10 8 „ ,,45*0 „ 



r(min.) = 2-lxl0 8 „ „ 124 „ 



These numbers are not consistent amongst themselves, nor 



* Ewers employed a grid over his active materials in order to prevent 

 rays from affecting tbe experiment unless they were emitted within a 

 certain angle. He was unaware of the existence of the secondary delta 

 rays ; if these are taken into account it appears that rays must have been 

 emitted in all directions from the surface of his grid. The allowance 

 made for ihis fact accounts for part of the discrepancy between the 

 values calculated bv him and those calculated here. 



