200 ELECTRICAL PHENOMENA [CH. xxi. 



gradient of potential, it might be possible to get 

 evidence of an approach to a saturation-current- 

 density in liquids. The observed accuracy of Ohm's 

 law* under such conditions, however, is against this 

 experimental possibility. 



Conclusion. 



The subject is very far from exhausted, but I 

 must not attempt to cover more ground. The 

 most exciting part of the whole is the explanation of 

 matter in terms of electricity, the view that electricity 

 is, after all, the fundamental substance, and that what" 

 we have been accustomed to regard as an indivisible 

 atom of matter is built up out of it ; that all atoms- 

 atoms of all sorts of substances are built up of the 

 same thing. In fact the theoretical and proximate 

 achievement of what philosophers have always sought 

 after, viz., a unification of matter is offering itself 

 to physical enquiry. But it must be remembered 

 that although this solution is strongly suggested 

 it is not yet a completed proof. Much more 

 work remains to be done before we are certain that 

 mass is due to electric nuclei. If it is, then 

 we encounter another surprising and suggestive 

 result, namely that the spaces inside an atom are 

 enormous compared with the size of the electrical 

 nuclei themselves which compose it ; so that an atom 

 ,- < can be regarded as a complicated kind of astronomical 

 system, like Saturn's ring, or perhaps more like a 



1 nebula; with no sun, but with a large number of equal 

 bodies possessing inertia and subject to mutual 



' electric attractive and repulsive forces of great mag- 

 nitude, to replace gravitation. The radiation of a 



* FitzGerald and Trouton, Brit. Assoc. Reports, 1886, 1887, 1888. 



