mined to
find out all we can about the mysterious ethereal medium supposed to
fill all space, and which conveys light and heat from one heavenly body
to another, but which yet evades all direct investigation. We are
peering into the law of gravitation itself with the full hope of
discovering something in its origin which may enable us to evade its
action. From time to time philosophers fancy the road open to success,
yet nothing that can be practically called success has yet been reached
or even approached. When it is reached, when we are able to state
exactly why matter gravitates, then will arise the question how this
hitherto unchangeable force may be controlled and regulated. With this
question answered the problem of the interaction between ether and
matter may be solved. That interaction goes on between ethers and
molecules is shown by the radiation of heat by all bodies. When the
molecules are combined into a mass, this interaction ceases, so that
the lightest objects fly through the ether without resistance. Why is
this? Why does ether act on the molecule and not the mass? When we can
produce the latter, and when the mutual action can be controlled, then
may gravitation be overcome and then may men build, not merely
airships, but ships which shall fly above the air, and transport their
passengers from continent to continent with the speed of the celestial
motions.

The first question suggested to the reader by these considerations is
whether any such result is possible; whether it is within the power of
man to discover the nature of luminiferous ether and the cause of
gravitation. To this the profoundest philosopher can only answer, "I do
not know." Quite possibly the gates at which he is beating are, in the
very nature of things, incapable of being opened. It may be that the
mind of man is incapable of grasping the secrets within them. The
question has even occurred to me whether, if a being of such
supernatural power as to understand the operations going on in a
molecule of matter or in a current of electricity as we understand the
operations of a steam-engine should essay to explain them to us, he
would meet with any more success than we should in explaining to a fish
the engines of a ship which so rudely invades its domain. As was
remarked by William K. Clifford, perhaps the clearest spirit that has
ever studied such problems, it is possible that the laws of geometry
for spaces infinitely small may be so di