the constant μ be supposed to have the value unity, the equations may be written
Eliminating E, we see[1] that H satisfies the equations
But these are precisely the equations which the light-vector satisfies in a medium in which the velocity of propagation is c1: it follows that disturbances are propagated through the model by waves which are similar to waves of light, the magnetic (and similarly the electric) vector being in the wave-front. For a plane-polarized wave propagated parallel to the axis of z, the equations reduce to
whence we have
,
these equations show that the electric and magnetic vectors are at right angles to each other.
The question now arises as to the magnitude of the constant c1.[2] This may be determined by comparing different expressions for the energy of an electrostatic field. The work done by an electromotive force E in producing a displacement D is
or .
per unit volume, since E is proportional to D. But if it be assumed that the energy of an electrostatic field is resident in the dielectric, the amount of energy per unit volume may be
↑For criticisms on the procedure by which Maxwell determined the velocity of propagation of disturbance, cf. P. Duhem, Les Théories Electriques de J. Clerk Maxwell, Paris, 1902.