564 A DYNAMICAL THEORY OF THE ELECTROMAGNETIC FIELD. 



using such words as electric momentum and electric elasticity in reference to 

 the known phenomena of the induction of currents and the polarization of 

 dielectrics, I wish merely to direct the mind of the reader to mechanical pheno- 

 mena which will assist him in understanding the electrical ones. All such phrases 

 in the present paper are to be considered as illustrative, not as explanatory. 



(74) In speaking of the Energy of the field, however, I wish to be under- 

 stood literally. All energy is the same as mechanical energy, whether it exists 

 in the form of motion or in that of elasticity, or in any other form. The 

 energy in electromagnetic phenomena is mechanical energy. The only question 

 is, Where does it reside ? On the old theories it resides in the electrified bodies, 

 conducting circuits, and magnets, in the form of an unknown quality called 

 potential energy, or the power of producing certain effects at a distance. On 

 our theory it resides in the electromagnetic field, in the space surrounding the 

 electrified and magnetic bodies, as well as in those bodies themselves, and is 

 in two different forms, which may be described without hypothesis as magnetic 

 polarization and electric polarization, or, according to a very probable hypothesis, 

 as the motion and the strain of one and the same medium. 



(75) The conclusions arrived at in the present paper are independent of 

 this hypothesis, being deduced from experimental facts of three kinds : 



1. The induction of electric currents by the increase or diminution of 

 neighbouring currents according to the changes in the lines of force passing 

 through the circuit. 



2. The distribution of magnetic intensity according to the variations of a 

 magnetic potential. 



3. The induction (or influence) of statical electricity through dielectrics. 



We may now proceed to demonstrate from these principles the existence 

 and laws of the mechanical forces which act upon electric currents, magnets, and 

 electrified bodies placed in the electromagnetic field. 



