a _nature_ different from the visible ones at the two ends
of the line? Is it not certain that the question is, How does the motion
get from one to the other, whether there be a wire or not? If there be a
wire, it is plain that there is motion in it, for it is heated its whole
length, and heat is known to be a mode of motion, and every molecule
which is thus heated must have had some antecedent motions. Whether it
be defined or not, and whether it be called by one name or another, are
quite immaterial, if one is concerned only with the _nature_ of the
action, whether it be matter or ether, or motion or abracadabra.

Once more: suppose we have a series of active machines. (Fig. 11.) An
arc lamp, radiating light-waves, gets its energy from the wire which is
heated, which in turn gets its energy from the electric current; that
from a dynamo, the dynamo from a steam-engine; that from a furnace and
the chemical actions going on in it. Let us call the chemical actions A,
the furnace B, the engine C, the dynamo D, the electric lamp E, the
ether waves F. (Fig. 12.)

[Illustration: FIG. 11.]

The product of the chemical action of the coal is molecular motion,
called heat in the furnace. The product of the heat is mechanical motion
in the engine. The product of the mechanical motion is electricity in
the dynamo. The product of the electric current in the lamp is
light-waves in the ether. No one hesitates for an instant to speak of
the heat as being molecular motion, nor of the motions of the engine as
being mechanical; but when we come to the product of the dynamo, which
we call electricity, behold, nearly every one says, not that he does not
know what it is, but that no one knows! Does any one venture to say he
does not know what heat is, because he cannot describe in detail just
what goes on in a heated body, as it might be described by one who saw
with a microscope the movements of the molecules? Let us go back for a
moment to the proposition stated early in this book, namely, that if any
body of any magnitude moves, it is because some other body in motion and
in contact with it has imparted its motion by mechanical pressure.
Therefore, the ether waves at F (Fig. 11) imply continuous motions of
some sort from A to F. That they are all motions of ordinary matter from
A to E is obvious, because continuous matter is essential for the
maintenance of the actions. At E the motions are handed over to the
ether, and they are radiat