10 On a Fourth State of Matter. [Jan. 27, 



all as corpuscular radiations of some sort, and we then look upon 

 our researches into their l^ehaviour as attempts to under?tand the 

 collisions of the various new corpuscles with the constituent centres 

 of force in the atoms. But if we ascribe corpuscular properties to 

 the y and x rays, we are led far away from the original speculations 

 as to their nature. Stokes supposed them to be spreading aether 

 pulses, but in his theory the energy of the pujse spreads on ever- 

 widening surfaces as the time passes, and is utterly insufficient to 

 provide the energy of the /? rays which the y or x rays excite. Some 

 sort of mechanism has to be devised by which the energy of the 

 y ray moves on without spreading, so that at the fateful moment it 

 may be all handed over to the /3 ray, which carries it on. I had the 

 hardihood myself to propose a theory of this kind. My idea was 

 that the y or a; ray might be considered as an electron which had 

 assumed a cloak of darkness in the form of sufficient positive elec- 

 tricity to neutralize its charge. Nor do I see any I'eason for 

 al}andoning this idea, for it is at least a good working hypothesis. 

 It means, of course, that not only does the energy of the fS ray come 

 from the y ray, but the /3 ray itself. 



Many insist that my neutral corpuscle is too material, and that 

 something more ethereal is wanted. For it appears that ultra-violet 

 light possesses many of the properties of x and y rays. It can excite 

 electrons to motion, and sometimes the speed of the electron depends 

 on the quality of the light and not on the nature of the material 

 from which it springs. They propose, therefore, a quasi-corpuscular 

 theory of hght, y and x rays being included. The immediate objection 

 to this proposal is that it seems to throw away at once all the marvel- 

 lous explanations of interference and diffraction which Young and 

 Fresnel founded on a theory of spreading waves ; and I do not think 

 anyone has yet made good "this defect. The light corpuscle which is 

 proposed is a perfectly new postulate. It is to move with the 

 velocity of light, keeping a circumscribed and invariable form, to 

 have energy and momentum, and to be capable of replacing and 

 l)eing replaced by an electron which possesses the same energy but 

 moves at a slower rate ; and, of course, it has to do all that the old 

 light-waves did. The whole situation is most remarkable and 

 puzzling. We are w'orking and waiting for some solution which, 

 perhaps, will come in a moment unexpectedly. Meanwhile, we must 

 just try to verify and extend our facts, and be content to piece 

 together parts of the puzzle, since we cannot, as yet, manage the 

 whole. My object to-night has been to show you how we may 

 conveniently bind together a large number of the phenomena of 

 radioactivity into an easily-grasped bundle, using a kinetic theory 

 which has many points of resemblance to the older kinetic theory of 

 gases. 



[W. H. B.] 



