THE ETHER AND MATTER POINCARE. 201 



no further mystery. Therefore the atom of tlie chemist woukl not 

 have satisfied him since that is not indivisible; it is not a true element ; 

 it is not free from mystery, from secrets. The chemist's atom is a 

 universe. Democritus would have considered, even after so much 

 trouble in finding it, that we were still only at the beginning of our 

 search — these pliilosophers are never satisfied. 



And so the second thought wliich comes home to us is that eacli 

 new physical discovery brings added complexity to the atom. To 

 begin with, these bodies, v/hich we believed simple, and wliich indeed 

 do act in many ways hke simple bodies, may be separated into yet 

 simpler components. Tliis atom disintegrates into yet smaller 

 atoms. What we caU radioactivity is the perpetual breaking up 

 of atoms. It is sometimes spoken of as a transmutation of elements; 

 that is not strictly correct because an element is not really trans- 

 formed into another element; it is really decomposed into several 

 others. The products of the decomposition are still chemical atoms, 

 similar in many respects to the more complex one, wliich in breaking 

 up gave birth to them. It is a phenomenon which may be ex])ressed 

 by the most common kind of a reaction by a chemical equation 

 which would be accepted with very httle hesitation by the most 

 conservative chemist. 



Nor are we yet done, for witliin the atom we find yet more — elec- 

 trons. Each atom is like a sort of solar system where the small 

 negative electrons play the role of planets revolving around the great 

 positive central electron which takes the place of our sun. It is 

 because of the mutual attraction of these electricities of opposite 

 sign that the system is bound together as a whole. This attraction 

 governs the periods of the planets and these periods fix the wave 

 lengths of the light emitted by tlie atom. It is because of the self- 

 induction of the currents fomied by the moving electrons that the 

 atom so formed has an apparent inertia wldch v/e caU its mass. 

 Besides these captive electrons there are others wluch are free and 

 subject to the ordinary kinetic laws of gases ami whicli render metals 

 con(h!ctive. The second class are like the comets v/hich circulate 

 from one stellar system to another, estabUsliing tlius an exchange of 

 energy between distant systems. 



But we have not yet come to an end. Besides these electrons, or 

 atoms of electricity, we find magnetons, or atoms of magnetism, 

 wliich we meet to-day through two different paths; through the 

 study of magnetic substances and through the study of tlie spectra 

 of simple bodies. I need not remind you of the beautiful discussion 

 of Weiss and the astonishing relationsliips and commensurabilities 

 which his experiments sliowed in such an unexpected manner. 

 There were numerical relationships which could not be due to chance, 

 and for wliich an explanation had to be sought. 



