IS IXAUGUUAL ADDRESS. 



rays. Foi- these and other reasons it is no longer thought possible that 

 the energy of the electrons, which arise in this wa}--, can come from 

 the atoms themselves; it is simply derived from the Rontgen or 

 samma ravs, as the case mav be. 



But if the energy is derived from this source, we cannot allow that 

 the Rontgen rays spread as thought at first. The energy of a Rontgen 

 ray must move in a straight line without loss by the way, so that when 

 it strikes the fatal atom it may have an undiminished amount to give 

 to tlie electron which takes its place, and the velocity of the latter may 

 not depend on the distance the ray has travelled fi-om the tube. The 

 X ray, in fact, behaves like a material particle, in that it moves from 

 point to point, carrying a certain store of energy which does not 

 diffuse over a larger space in the transit. Now, the aether, which is 

 supposed to fill all space, and which has been postulated in order to 

 carry the light and heat radiations, has hitherto been supposed to be 

 quite uniform and isotropic. A disturbance which has its ongin at 

 any point spreads in widening spheres, diffusing and weakening as it 

 goes. Our conception of the cether must be materially amended if we 

 are to suppose it capable of canying a pulse along a line without 

 allowing it to spread. Thomson has not shrunk from making this very 

 serious change, and has imagined the sether to possess a sort of fibrous 

 or tubular structure ; in other words, he has filled all space with lines 

 or tubes, along which the tether pulse is to travel undiffused. This 

 carries with it corresponding changes in our conception of light and 

 heat. We must replace our spx-eading waves by clouds of minute 

 bundles of energy, tiny entities which move like material particles, but 

 with the speed of light. It is a curious and most interesting return in 

 the direction of the old Newtonian coi-puscular hypothesis — a kind of 

 compromise between two theories which were so long at war. 



But the question arises at once: Is the amended hypothesis able 

 to explain all the facts ? In our ignorance of the nature of the aether 

 it might, perhaps, just as well have such a constitution as not. Recent 

 experiment has, however, added largely to our knowledge of the cir- 

 cumstances under which the energy of a moving electron is converted 

 into the energy of a pulse and back again, and it is right to ask 

 whether they are in agreement with the amended theory. So far as I 

 am able to judge, no satisfactory agreement is possible ; but it is only 

 fair to say that the experimental results to which I refer have been 

 obtained so recently that there has not been time for the advocates of 

 the pulse theory to make any serious attempt to explain them. 



I will describe some of these experimental results presently. 

 Meanwhile, I would ask you to consider the Rontgen and gamma rays 



