ght, yet electricity can traverse miles of
steel in the fraction of a second. "Gravity" seems the only energy which
cannot be isolated by some means or other. No substance is opaque to
gravity. It acts through all substances, at all times, continuously. In
this respect telepathy may resemble gravitation.[43] If this were true,
or anything like it were true, we could easily see why a solid
substance, such as the human skull, might offer no appreciable
resistance to the passage through it of undulations of a certain
velocity--of a speed so great, perhaps, that they could not be detected
by any of the instruments at the command of the physicist today.

But there are other and still more serious objections to the vibratory
action of telepathy which have not as yet been mentioned. For if we try
to push the analogy further, we shall find that it is by no means so
clear as might be supposed. Thus in the case of wireless telegraphy the
vibratory action of the ether is a purely mechanical process and does
not carry emotion, thought, or intelligence with it--being vibration
pure and simple. Now, in the case of a supposed telepathic message,
thought flashed from one brain to another must be supposed to convey
with it intelligence of some sort; for if it were a _purely_ mechanical
vibratory action, how is it that this would impress another brain in
such an entirely different manner from all other vibrations as to
create in that brain not only a thought, but the precise _kind_ of
thought--the _replica_ of the thought--which originated in the brain of
the agent? Granting that vibrations are but "symbols," and that they are
interpreted by our brains _as_ things, the difficulty remains that, in
all other cases, such vibrations, no matter what their intensity, convey
to the brain the idea of external objects, or qualities of those
objects, and do not convey to it the idea of mind or intelligence. How
is it, therefore, that one particular species of vibration, which, we
must assume, would vary more or less with each individual, can convey
with it the idea of thought, and that this vibration is associated with
mind, and in fact is thought, while all other vibrations in the world
are in nowise connected with intelligence and do not appear to us to be
so connected? And further, how infinitely we should have to vary the
degree and type of vibration to correspond to all shades of thought and
feeling and emotion! Sir William Crookes some years