5O TWO NEW WORLDS 



electrons, which periodically subject them to a 

 greater repulsion as they approach them in what 

 we call " conjunction," As a general rule, these 

 perturbations, like those in the solar system, are 

 not serious, being outweighed by the much greater 

 attraction of the central body, and also, to some 

 extent, by the electrodynamic ("magnetic") attrac- 

 tion between the moving electrons. But every now 

 and then it will happen that a larger number of 

 electrons are in conjunction together, and then the 

 outermost ones will stand in danger of being expelled 

 from their orbits and set roaming at large. The 

 likelihood of such a contingency happening depends, 

 of course, upon a variety of circumstances, such as 

 the structure and size of the central body, the dis- 

 tribution and number of the electrons, &c. It may 

 well happen that as the central body increases in 

 mass the likelihood of expulsion oscillates between 

 a number of maxima and minima. At the minima 

 the system would have the greatest ability to take up 

 an extra electron ; but this process would be much 

 rarer than the loss of electrons, owing to the repul- 

 sion of the other electrons which would have to 

 be overcome. In short, it is much easier for a 

 neutral system to lose an electron than to acquire 

 an extra one. 



Here we have, then, something like an explanation 

 of the Periodic Law in its electro-chemical aspect. 

 As we proceed from lower to higher atomic weights, 



