Mechanism of Radiation. 455 



atom consists exclusively of negative ions, but there still 

 remains the question as to why it is that the positive ions 

 rather than the negative are excluded from the outermost 

 shells o£ the atom; we have not yet removed the essential 

 difference in quality between positive and negative ions. 



We cannot suppose that all atoms with positive ions at the 

 surface are unstable ; for corresponding to any stable arrange- 

 ment with negative ions at the surface, there must be a stable 

 arrangement which is exactly the same except that the sign 

 of every ion is changed. If an ordinary atom is referred to 

 as a positive atom, this other kind of atom may be referred 

 to as a negative atom. 



Let us refer to the atoms of the various chemical elements 

 as A, B, C, . . . . , and let the imaginary corresponding negative 

 atoms be referred to as A', B', C, . . . . In order that a system 

 of chemical elements A, B, C, . . . . may have a permanent 

 existence it is not only necessary that the individual atoms 

 A, B, C, . . . . shall each be statically stable, but also that when 

 any atom A meets another atom B, the atoms A and B shall 

 not lose their identity. Now the forces exerted between A 

 and B when in proximity will arise mainly from that part of 

 the potential-function which represents the divergence of the 

 forces exerted by the ions near the point of closest approach 

 from those calculated on the ordinary electrostatic law, and 

 will possibly depend largely upon the signs of the ions in 

 these outermost shells. Thus if A and B do not unite so 

 closely as to lose their separate identity, it is not difficult to 

 imagine that A' and B would be drawn together until a 

 complete rearrangement of ions had been effected and a new 

 atom or atoms formed. If this supposition be accepted it will 

 be clear that a condition that a system of elements should 

 have a permanent existence is that the outermost layers of all 

 the atoms shall be of the same sign. We can imagine a 

 number of positive and negative ions initially scattered at 

 random in space to condense into matter of both kinds, but 

 whenever a collision takes place between two atoms of different 

 kinds, the result is a rearrangement of parts, until finally only 

 one class of matter is left in the field. 



This last suggestion is ot a very speculative kind ; but it may 

 be noticed that if matter is an aether-structure, and if the 

 difference between positive and negative electricity only enters 

 in the aether-equations through a mere difference of sign, 

 then the observed difference between the relations of the two 

 kinds of electricity to material phenomena can only arise 

 from a difference in the initial conditions, such as that just 

 described. 



