496 Scientific Proceedings, Royal Dublin Society. 



to do more than mention the facts that the -y radiation given out by radio- 

 active atoms sliows continnous as well as line spectra and that the j3 radiation 

 of such atoms possesses a varied distribution of velocity which, when analyzed 

 by the deflecting influence of a strong magnetic field, gives rise to a linear 

 " spectrum " of velocities, superimposed on a continuous " spectrum " of 

 velocities. Further, it can be shown that tlie energies characterizing the lines 

 in tlie " spectra " of the primary /3 particles escaping from a radioactive 

 atom — for instance, Ea C — are such as -would be derived from an integral 

 number of the quanta associated with certain lines of the 7 ray spectrum 

 emitted by this same element. Hence the emission of trains of waves (and 

 of quanta) from such atoms is indicated ; 10 or even more waves entering 

 iuto the train according to the nature of the atom and tlie frequency.^ Under 

 suitable conditions tlie train of waves may give all its energy to a single 

 high-speed electron. The high penetrating power of the jS particle 

 excited in matter by the y ray has, according to this view, its source in the 

 peculiar structure of the y ray emitted by the radioactive atom. 



The foregoing statements define in a brief — perhaps too brief — manner 

 the fundamental facts of photo- and radio-electricity. The most important 

 of these facts to carry in mind is the convertible nature of the two sorts of 

 radiation — the electronic and the vibratory. It helps our assimilation of the 

 laws governing this interchange to remember that the activity involved in 

 the y, X, or light rays is parcelled out into definite quanta which are mucli 

 greater for the high frequencies than for the low ; so that the /3 rays 

 originating in the interchange possess much more energy in the one case than 

 in the other. 



We must now direct our attention to the electron and its influence in 

 bringing about molecular changes. Here, again, we deal in quanta — 

 although differing in kind from the Planok unit. For Faraday long ago 

 showed reasons for assuming that electric currents attending chemical or 

 molecular changes moved in quanta: I lie Faraday charge on the ion, wliich — 

 as we have already seen — is the same in amount as that which is associated 

 with the electron. Thus we find Nature on every side ultimately ordered in 

 discontinuous units. 



The simplest case in wldch we can study the effect of tlje electron is when 

 it is liberated in a gas— sa}', air. Each electron liberated from an atom of 

 oxygeu or nitrogen leaves this atom positively electrified by one unit cliarge 

 of positive electrification. The atom becomes a positive ion. The electron soon 

 attaches itself to one or more atoms, and in doing so creates a negative ion. 



' Eutherford, lac. eit. 



