122 PHYSICS OF THE ELECTRON 



I. The Electromagnetic Ether 



(1) Fields and Charges. One can say that the combined efforts of 

 Faraday, Maxwell, and Hertz have resulted in giving us a precise 

 knowledge of the properties of the electromagnetic ether, and of 

 light; of a medium, homogeneous and void of matter, whose state 

 is completely defined, with the exception of gravitation, when we 

 know at any point the direction and magnitude of the electric and 

 magnetic fields. 



I insist, for the present, on the possibility of arriving at a concep- 

 tion of fields of force, as well as the related idea of electric charges, 

 independently of all dynamics; I wish by this to imply only a know- 

 ledge of the laws of motion and of matter. 



The two fields possess this property, that their divergence is zero in 

 all parts of the ether; that is to say, the flux of electric and mag- 

 netic force is rigorously zero across a closed surface which does not 

 contain any matter in its interior. It is in fact always matter in the 

 ordinary sense of the word which contains and can furnish the electric 

 charges around which the divergence of field exists whose direction 

 varies with the sign of the charges. 



In extreme cases where the electric charges appear to be most 

 completely separated from their material support, as in the case 

 of the cathode rays for example, the experimental fact of the 

 granular structure of these rays and the complete indestructibility 

 of their charge, the fact finally that cathodic particles are charges 

 possessing the fundamental property of matter, inertia, and expe- 

 riencing acceleration in the electromagnetic field, these facts do not 

 allow us to distinguish their charge from the so-called free charge 

 of ordinary electrified matter. 



Furthermore, we shall come to the idea not only that there can be 

 no electric charge without matter, but that, in fact, there can be no 

 matter without electricity, an aggregation of electrical centres of the 

 two kinds. Electrons, analogous to the cathode particles, possess 

 almost all the known properties of matter by the fact alone that 

 these centres are electrified. We shall see within what limits this con- 

 ception can be considered sufficiently known, and if it is necessary to 

 superimpose other properties on those which result from electrically 

 charged centres in order to obtain a satisfactory representation of 

 matter; the ether alone, on the contrary, never contains any electricity. 



If experiment obliges us to admit the existence of electric charges, 

 positive and negative, from the flux of electric force different from 

 zero across a closed surface drawn entirely in the ether and con- 

 taining matter, it is otherwise for the magnetic field. Experiment 

 has never furnished an instance where a closed surface drawn in the 

 ether was traversed by a magnetic field different from zero. One 



