﻿Mr. Norman Campbell on Delta Hays. 59 



is greater than the emergent radiation, as was asserted in the 

 previous paper. It' the results of that paper are calculated 

 according to (1), it appears that there also the radiations are 

 nearly equal, the emergent (and not the incident) showing 

 a slight preponderance. The results of method (1) certainly 

 inspire the greater confidence, for those of method (2) 

 depend entirely upon the value for " V = 0' s ; it has been 

 already noted that the values of this point are much more 

 variable than those of any other, and the hypotheses advanced 

 in the foregoing paragraphs would tend to account for the 

 variability. According to these hypotheses the position of 

 that point is largely influenced by differences in the surface 

 conditions, which determine the ease with which the electrons 

 can escape. In these circumstances there seems no evidence 

 left for the view that the incident is greater than the 

 emergent radiation, or indeed for the view that the two are 

 not equal. 



12. One curious point, "which is difficult to explain, and 

 while unexplained renders somewhat uncertain all con- 

 clusions as to the quantity of the radiation, must be 

 mentioned. It will be noted that the values calculated by 

 (1) for the emergent radiations from the various metals 

 when the lower electrode is covered with soot do not agree 

 with the values calculated by the same method of the same 

 quantity when both electrodes are of the same material. 

 They agree rather with the calculated values of the incident 

 radiation according to (2) when both electrodes are the same. 

 The only explanation I can suggest is that, when the elec- 

 trodes are the same, the value for " V = " and not that for 

 " V = (magnet) " gives the value for the current in such cir- 

 cumstances that none of the rays from one electrode strike 

 the other ; such would be the case if the rays were unable to 

 escape at all from a metal surface without the aid of a field. 

 But in that case it is difficult to see why the application of 

 the magnetic field should change the current. It is possible 

 also that the discrepancy is connected in some way with the 

 fact that the electrode B consisted always of a very thin 

 sheet of the material, while A was covered with a much 

 thicker sheet. Hauser (he. eit.) has concluded that the 

 delta rays have an appreciable penetration, and that the full 

 amount of them is not emitted from a sheet until it has 

 reached a considerable thickness. The evidence for this view 

 seems inconclusive, but in the light of these observations 

 it cannot be rejected summarily. It might explain the fact 

 that it appears from these experiments as if the total 

 amount of delta radiation varied somewhat with the material 



