442 Prof. W. H. Bragg an the Properties and 



It has been suggested to me by /my colleague Dr. Rennie that 

 the rayless changes of Ra may really be accompanied by the 

 emission of neutral pairs of very small moment. This adds 

 another unknown factor to the calculation. The energy in- 

 volved in such emissions might be quite small, and, moreover, 

 if pairs can be taken up into atoms, so as to form new atoms, 

 the whole of the energy may not appear as heat. 



It is interesting to carry the speculation a little further 

 and to observe that a pair possessing a very circumscribed 

 field might cause little or no ionization, and be capable of 

 very great penetration. Its end might be incorporation with 

 an atom traversed : Professor Rutherford has suggested to 

 me that such a fate may befall the u particle at the end of 

 its range. On this view it would be possible for a portion 

 of a disintegrating atom to break away, to pass over an 

 appreciable distance, and finally to become part of another 

 atom, the atomic weight of which would be thereby increased. 

 Internal atomic energy might be transferred at the same 

 time. For if we suppose that it is possible for some of the 

 internal energy of an atom to be set free, and recent dis- 

 coveries seem to compel the supposition, then we must also 

 consider it possible for atoms to withdraw energy from 

 circulation and add it to their internal store. If, therefore^ 

 the handing of neutral pairs from one atom to another is 

 a process which actually occurs, then matter and energy 

 may be continually transferred from atom to atom without 

 our being aware of it : the whole operation may take place 

 in a world apart. We cannot follow it by radioactive tests, 

 for the ionization may be so feeble : nor chemically^ because 

 the quantity of atomic change may be so slow ; nor thermally 9 

 because the energies appear at no stage in tangible form. 



Since the properties of y rays are amongst the properties 

 of X rays, an hypothesis which will suit one form of radiation 

 will also so far suit the other. But we know much more 

 about the latter form of radiation than we do about the 

 former. It is of interest, therefore, to consider the extent 

 to which our additional knowledge can be fitted to a neutral 

 pair hypothesis. It is true, of course, that the aether pulse 

 theory has been most ably developed, and is now widely 

 accepted. Nevertheless the evidence for it is all indirect : 

 and indeed some of it is, I think, a little over-rated. It is 

 quite possible that aether pulses may not, after all, constitute 

 the bulk of Rontgen radiation. If, therefore, there is any- 

 thing to be said in favour of any other hypothesis, it seems 



right that it should be said and considered 



