178 Dr, J. A. Fleming [May 30, 



motion round each other, in fact that each atom is a miniature solar 

 system. 



Against this view, however, Mr. T. H. Jeans * has pointed out 

 that an infinite number of vibrations of the electrons would be possible 

 about each state of steady motion and hence the spectrum of a gas 

 would be a continuous one and not a bright-line spectrum. 



If we are to assume an atom to consist wholly of positive and 

 negative electrons or point charges of electricity, Mr. Jeans has 

 suggested that we may obtain a stable structure by postulating that 

 the electrons, no matter whether similar or dissimilar, all repel each 

 other at very small distances. 



We might then imagine an atom to be built up of concentric 

 shells of electrons like the coats of an onion alternately positive and 

 negative, the outermost layer being in all cases negative. The differ- 

 ence between the total number of positive and negative electrons is 

 the valency of the atom. 



On this view an atom of hydrogen would consist of from 700 to 

 1000 positive and negative electrons arranged in concentric layers in 

 a spherical form. The vibrations which emit light are not those of 

 the atom as a whole but of the individual electrons which compose it. 



The reason for assuming that in all cases the outermost layer of 

 electrons is negative is that if it were not so, if some atoms had their 

 outer layers of negative and some of positive electrons, two atoms when 

 they collided would become entangled and totally lose their indivi- 

 duality. There would be no permanence. Hence our present atoms 

 may be, so to speak, the survivors in a struggle for existence which 

 has resulted in the survival only of all atoms which are of like sign 

 in the outer layer of electrons. We see an instance of a similar 

 action in the case of the like directed rotation of all the planets round 

 the sun which is due to the operation of the law of conservation of 

 angular momentum. As a consequence of the equality of sign of the 

 outer layer of electrons two atoms cannot approach infinitely near to 

 each other. They mutually repel at very small distances. This 

 suggestion affords a possible clue to the reason why we only know at 

 present free negative electrons ; it is because we can only detach a 

 corpuscle or electron from the outer layer of an atom. It is clear, 

 however, that the complete law of mutual action of electrons has yet 

 to be determined. We have also to account for gravitation, and this 

 involves the postulate that all atomic groups of electrons without 

 regard to sign must attract each other. Hence we need some second 

 Newton who shall formulate for us the true law of action of these 

 electrons which form the " foundation stones of the material universe." 

 Facts seem to suggest that the complete mathematical expression for 

 the law of mutual action of two electrons must show : 



1. That at exceedingly small distances they must all repel each 

 other without regard to sign. 



' Moi^haniam of Radiation,' Proc, Phys. Soc, Lond., vol. xvii. p. 760. 



