stops, the field
adjacent is destroyed. Another closure develops the field again, which,
like the other, travels outwards; and so there may be formed a series of
waves in the ether, each 186,000 miles long, with an electro-magnetic
antecedent. If the circuit were closed ten times a second, the waves
would be 18,600 miles long; if 186,000 times a second, they would be but
one mile long. If 400 million of millions times a second, they would be
but the forty-thousandth of an inch long, and would then affect the eye,
and we should call them light-waves, but the latter would not differ
from the first wave in any particular except in length. As it is proved
that such electro-magnetic waves have all the characteristics of light,
it follows that they must originate with electro-magnetic action, that
is, in the changing magnetism of a magnetic body. This makes it needful
to assume that the atoms which originate waves are magnets, as they are
experimentally found to be. But how can a magnet, not subject to a
varying current, change its magnetic field? The strength or density of a
magnetic field depends upon the form of the magnet. When the poles are
near together, the field is densest; when the magnet is bent back to a
straight bar, the field is rarest or weakest, and a change in the form
of the magnet from a U-form to a straight bar would result in a change
of the magnetic field within its greatest limits. A few turns of
wire--as has been already said--wound about the poles of an ordinary
U-magnet, and connected to an ordinary magnetic telephone, will enable
one, listening to the latter, to hear the pitch of the former loudly
reproduced when the magnet is struck like a tuning-fork, so as to
vibrate. This shows that the field of the magnet changes at the same
rate as the vibrations.

Assume that the magnet becomes smaller and smaller until it is of the
dimensions of an atom, say for an approximation, the fifty-millionth of
an inch. It would still have its field; it would still be elastic and
capable of vibration, but at an enormously rapid rate; but its vibration
would change its field in the same way, and so there would be formed
those waves in the ether, which, because they are so short that they can
affect the eye, we call light. The mechanical conceptions are
legitimate, because based upon experiments having ranges through nearly
the whole gamut as waves in ether.

The idea implies that every atom has what may be loosely ca