ELECTRONIC THEORY OF ELECTRICITY. 13 



association with masses as large as atoms, but negative electricity is 



identified with corpuscles or masses only a small fraction of the size of 



an atom. This does not prove that an atom may not include positive 



corpuscles or electrons, but only that so far we have not been able to 



isolate them. . . 



The Electronic Theory of Electricity. 



From this point of view a theory of electricity originates called the 

 electronic theory. The principal objects of consideration in this theory 

 are these electrons which constitute what we call electricity. An atom 

 of matter in its neutral condition has been assumed to consist of an 

 outer shell or envelope of negative electrons associated with some core 

 or matrix which has an opposite electrical quality, such that if an elec- 

 tron is withdrawn from the atom the latter is left positively electrified. 



A neutral atom minus an electron constitutes the natural unit of 

 positive electricity and the electron and the neutral atom minus an 

 electron are sometimes called negative and positive ions. Deferring for 

 a moment a further analysis of possible atomic structure we may say 

 that with the above hypothesis in hand we have then to express our 

 statements of electrical facts in terms of the electron as the fundamental 

 idea. 



All that can be attempted here is a very brief exposition of the suc- 

 cess which has so far attended this effort to create a new range of elec- 

 trical conceptions. Let us consider first the fundamental difference 

 between substances in respect of electrical conductivity. In the elec- 

 tronic theory what is the distinction between conductors and non-con- 

 ductors? It must be remembered that on the electronic hypothesis an 

 electric current is a movement of electrons. Hence a conductor must 

 be a substance in which electrons free to move exist. It is considered 

 therefore that in metals and good conductors a certain proportion of the 

 atoms are broken up into positive and negative ions or into electrons 

 and remainders of atoms which we may call coelectrons. There may be 

 a constant decomposition and recomposition of atoms taking place, and 

 any given electron so to speak flits about, now forming part of one atom 

 and now of another and anon enjoying a free existence. It resembles a 

 person visiting from house to house forming a unit in different house- 

 holds and in between being a solitary person in the street. In non- 

 conductors on the other hand the electrons are much restricted in their 

 movements, and can be displaced a little way but are pulled back again 

 when released. The positive and negative ions or electrons and 

 coelectrons never have the opportunity to part company very far. 



The reader who is familiar with the modern doctrine of the ioniza- 

 tion of salts in solution will see that a close similarity exists between 

 this view of the atomic state of a metal and the chemical state of a 

 salt in solution. The ionic theory of solution is that if some salt, say 



