body placed in
the liquid, or acting on it, which confers upon it the property of
viscosity; the hand would no longer move freely. During its motion, but
then only, resistance would be encountered and overcome. Here we have
rudely represented the case of the excited magnetic field, and the
result in both cases would be substantially the same. In both cases heat
would, in the end, be generated outside of the muscle, its amount being
exactly equivalent to the resistance overcome.

Let us push the analogy a little further; suppose in the case of the
fluid rendered viscous, as assumed a moment ago, the viscosity not to be
so great as to prevent the formation of ripples when the hand is passed
through the liquid. Then the motion of the hand, before its final
conversion into heat, would exist for a time as wave-motion, which, on
subsiding, would generate its due equivalent of heat. This intermediate
stage, in the case of our moving wire, is represented by the period
during which the electric current is flowing through it; but that
current, like the ripples of our liquid, soon subsides, being, like
them, converted into heat.

Do these words shadow forth anything like the reality? Such speculations
cannot be injurious if they are enunciated without dogmatism. I do
confess that ideas such as these here indicated exercise a strong
fascination on my mind. Is then the magnetic field really viscous,
and if so, what substance exists in it and the wire to produce the
viscosity? Let us first look at the proved effects, and afterwards turn
our thoughts back upon their cause. When the wire approaches the magnet,
an action is evoked within it, which travels through it with a velocity
comparable to that of light. One substance only in the universe has
been hitherto proved competent to transmit power at this velocity;
the luminiferous ether. Not only its rapidity of progression, but its
ability to produce the motion of light and heat, indicates that the
electric current is also motion.[1] Further, there is a striking
resemblance between the action of good and bad conductors as regards
electricity, and the action of diathermanous and adiathermanous bodies
as regards radiant heat. The good conductor is diathermanous to the
electric current; it allows free transmission without the development of
heat. The bad conductor is adiathermanous to the electric current, and
hence the passage of the latter is accompanied by the development of
heat. I