r of the universe. We
have seen, therefore, that as the sun is an electrified body, so all the
planets and satellites are electrified bodies also, each possessing its
own field, with all that such a field implies.

We shall find that such a conception is borne out by experience and
observation, when we come to deal with the Earth as a magnet; because we
shall afterwards learn that the Earth is an electro-magnet, possessing
its magnetic field, which is co-existent and equipollent with its
electric field.

[Footnote 28: _Exp. Res._, 1297, 1298.]

[Footnote 29: Par. 1298.]

ART. 82. _Energy of the Field._--We have seen in Art. 79 that every
electrified body has an electric field. We have further learned, in
carrying the electro-magnetic theory of light to its logical conclusion,
that all the planets and satellites together with the sun must be
electrified bodies, each possessing its electric field.

We have now to determine the effect of such a truth from its dynamical
aspect upon the bodies within the field, that is to say, we have to
consider the energy of such electric fields, and endeavour to find out
the effect of such energy upon other bodies within that field.
Maxwell,[30] in his introduction to a paper on "The Dynamical Theory of
the Electro-magnet Field," writes on the matter thus: "It appears
therefore that certain phenomena in electricity and magnetism lead to
the same conclusion as those of optics, namely, that there is an
aetherial medium pervading all bodies and modified only in degree by
their presence; that the parts of this medium are capable of being set
in motion by electric currents and magnets; that this motion is
communicated from one part of the medium to another by forces arising
from the connection of these parts; that under the action of these
forces, there is a certain yielding depending upon the elasticity of
these connections; and that therefore energy in two different forms may
exist in the medium, the one form being the actual energy of motion of
its parts, and the other being the potential energy stored up in the
connections in virtue of their elasticity."

The two forms of energy he gives us in his work on _Magnetism and
Electricity_, where, in the quotation already given in Art. 79, he
states them to be electro-static and electro-kinetic energy, while in
paragraph 792 of the same work he adds: "The intrinsic energy of the
medium is half electro-static and half electro-kinetic, tha