upon another; the exertion of
Force by one body on another, the transfer of motion and energy from one
body to another, any kind of effect, no matter what, which can be
produced in one body by means of another, whether the bodies be animate
or inanimate."

"Now I wish to appeal to this mass of experience, and to ask, Is not the
direct action of one body on another across empty space, and with no
means of communication whatever, is not this absolutely unthinkable? We
must not answer the question offhand, but must give it due
consideration, and we shall find, I think, that wherever one body acts
on another body by obvious contact, we are satisfied and have a feeling
that the phenomena is simple and intelligible, and that, whenever one
body apparently acts on another body at a distance, we are irresistibly
impelled to look for the connecting medium."

Again, on p. 333 of the same work, he adds: "Remember then, that
whenever we see a thing being moved, we must look for the rope. It may
be visible, or it may be invisible, but unless there is either a push or
a pull, there can be no action."

Now, in relation to celestial phenomena, we are confronted with the fact
of bodies acting on one another, and yet apparently they do not act upon
one another by or through a medium, and to that extent according to the
above extracts, such phenomena are opposed to universal experience.
Again, we find planets and satellites moving through space with more or
less uniform speed, and yet apparently there is no physical medium that
acts upon them with either a push or a pull, as the present conception
of the Aether is that of a frictionless medium, so that experience in
its widest form seems altogether opposed to the existence of a
frictionless medium.

Again, Tait in his _Natural Philosophy_ says: "The greater masses,
planets and comets moving in a less resisting medium, show less
indications of resistance. Indeed it cannot be said that observations
upon any one of these bodies, with the exception of Encke's Comet, has
demonstrated resistance. The greater masses, planets and comets moving
in a less resisting medium, show less indications. No motion in Nature
can take place without meeting resistance due to some if not all of
these influences. _The analogies of Nature and the ascertained facts of
physical science forbid us to doubt that every one of them, every star,
and every body of every kind has its relative motion impeded by the air,