16 INAUGURAL ADDRESS. 



important fact with exactness. Our divergences from the law are 

 under 1 per cent, so far, and it is not unlikely that, small as they are, 

 they are due to some disturbing influence in the experiment. Now, 

 the remarkable thing is that liutherford has shown that the alpha 

 particle, when it reaches the end of its range, is still possessed of 

 enormous speed, some thousands of miles per second, about half what 

 it started with. Then what has happened to it? Why can we no 

 longer follow it? The best suggestion is that of J. J. Thomson, that it 

 becomes neutralised by the attachment of an electron, and that when 

 neutral it does not excite delta rays. But this only sugge,sts a further 

 question of interest : What are now its prt)perties, and what its final 

 end? Somehow its speed is reduced, for Rutherford finds helium in 

 the tubes containing radium in the quantity to be expected if it is 

 derived from the alpha particles. Sometimes, perhaps, it is incorpo- 

 rated into an atom, helping to raise its atomic weight, and causing a 

 process the reverse of the known process of disintegration. It is verj- 

 curious that this loss of power occurs to the alpha particle, when its 

 velocity has fallen to the same amount, no matter what gas it is 

 moving through. 



Next let us consider the beta or cathode particle. In this case we 

 can follow many deflections from an original track, so that the particle 

 behaves more like a molecule of an ordinary gas. But, apparently, it 

 loses energy at every deflection, and, as it does so, deflections become 

 more numerous and more serious, and we can imagine that after a 

 very few scatterings it loses its speed aaid becomes incorporated in an 

 atom or molecule, forming the ordinary ion of which Dr. Pollock will 

 speak to you to-mon-ow. But there is also something else that can 

 happen to it. Like the alpha particle, it may disappear from view, 

 and in its place may appear a ray of dift'erent kind. When the cathode 

 rays are driven against the metal plate in the Eontgen ray tube, the 

 most of them dive into the metal and disappear; a few swing out and 

 hit the glass wall of the tube, which they do not penetrate, but, in the 

 case of a very few, we find their replacement by the famous Rontgen 

 or X rays. So, also, I think we may argue, from analogy, that beta 

 rays may disappear and be replaced by gamma rays, even though the 

 actual effect has never been observed. For, I think, it is easy to show 

 that the effect is too small to find. Not only is the number of particles 

 in a beta ray stream small compared to that in the cathode stream of 

 the X ray tube, but also the gamma rays which they produce are very 

 penetrating, and escape without being made to reveal their e.xistence. 



This transformation is, of course, a very remarkable thing. But 

 the interest is increased when we find that the reversed transformation 



