﻿56* Mr. Norman Campbell on Delta Rays. 



that the speed o£ the rays from different materials is the 

 same, though it cannot be estimated what difference in the 

 speed might escape detection. 



9. We may sum up the results of the foregoing discussion 

 as follows : — 



A great part of the change in the current due to a change 

 in the field between the electrodes is due to the dragging out 

 of tbe electrodes of delta rays generated in them which were 

 previously unable to escape. It is therefore quite illegiti- 

 mate to attempt to deduce from the potential difference 

 necessary to saturate the current any information as to the 

 maximum speed of the delta rays. Saturation is attained, 

 probably, when the field is sufficient to drag all the electrons 

 out of the electrodes, not when it is sufficient to prevent the 

 electrons crossing the space between the electrodes in opposi- 

 tion to the forces of the electric field. Experiments such as 

 these can give no information as to the maximum speed of 

 the rays. On the other hand an examination of the form of 

 the curves for small potential differences may give a minimum 

 estimate of that speed. The work of other investigators 

 leads to the conclusion that that speed is not less than that 

 corresponding to a potential difference of 3 volts. The 

 observations described here seem to prove that the properties 

 of the delta rays are quite independent of the speed of the 

 alpha rays exciting them, and lend no support whatever to 

 the view that the speed of the delta rays depends on the 

 material from which they are emitted. The experiments are 

 quite consistent with the view that the speed of the delta 

 rays is a universal constant *. 



10. So far as we have been concerned only with the quality 

 of the delta rays. The conclusions which we have reached 

 haA^e also important bearings on the results which were given 

 in the previous paper as to their quantity, more especially on 

 the question of the relative amounts of " incident " and 

 " emergent " radiation. 



Let Z be the current between the electrodes for " V = 0" 

 and 7J that for "V = (magnet) " ; let M-f- be the maximum 

 saturated positive current and M— the maximum saturated 

 negative current. Then on any view of the speed of the 

 delta rays, if the effect of the magnet is to prevent any of 

 the delta rays from one electrode reaching the other — reasons 

 will be given later for thinking that this condition is not 



* Tt is to be noted that this conclusion has been advanced by 

 "Wevtheimer recently {Pht/s. Zeit. xii. p. 411, 1911), and that the 

 reduction in the estimate of the speed of the rays which has been 

 suggested is favourable to his views. 



