(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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Cite as
J. C. Maxwell’s, ‘Dynamical theory of the electromagnetic field’, 1864. From The Royal Society, PT/72/7
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