J. C. Maxwell’s, ‘Dynamical theory of the electromagnetic field’

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                                (D) The value of the electromotive force in a <s>conductor<\s> body, as arising from the 
motion of <conductors<\s> the body in the field, the alteration of the field 
itself, and the variation of electric potential in the field. 
(E) The relation between electric displacement, and the 
electromotive force which produces it. 
(F) The relation between an electric current, and the electromotive 
force which produces it.
(G) The relation between the amount of free electricity at any 
point and the electric displacements in the neighbourhood. 
(H) The relation between the increase or diminution of free electricity 
and the electric currents in the neighbourhood. 

There are 20 of these equations in all, involving 20 variable 
quantities. 

(19) I then express in terms of these quantities the intrinsic energy 
of the Electromagnetic Field as depending partly on its magnetic 
and partly on its electric polarization at every point. 
From this I determine the mechanical force acting 
1st on a moveable conductor carrying an electric current; 
2nd on a magnetic pole; 
3rd on an electrified body. 

The last result, namely the mechanical force acting on an electrified 
body, gives rise to an independent method of electrical measurement 
founded on its electrostatic effects. The relation between the 
units employed in the two methods is shown to depend on what 
I have called the “electric elasticity” of the medium and to be a 
velocity, which has been experimentally determined by M.M. 
Weber & Kohlrausch. 

I then show how to calculate the electrostatic Capacity of a condenser 
and the specific inductive capacity of a dielectric. 
                            
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Manuscript details

Author
James Clerk Maxwell
Reference
PT/72/7
Series
PT
Date
1864
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J. C. Maxwell’s, ‘Dynamical theory of the electromagnetic field’, 1864. From The Royal Society, PT/72/7

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