nary every-day thoughts may be
the region of speculation which we have been called upon to traverse, we
have still kept within the limits of legitimate scientific hypothesis.
Though we have ventured for a goodly distance into the unknown, we have
not yet been required to abandon our base of operations in the known. Of
the views presented in the preceding paper, some are wellnigh certainly
established, some are probable, some have a sort of plausibility,
others--to which we have refrained from giving assent--may possibly be
true; but none are irretrievably beyond the jurisdiction of scientific
tests. No suggestion has so far been broached which a very little
further increase of our scientific knowledge may not show to be either
eminently probable or eminently improbable. We have kept pretty clear of
mere subjective guesses, such as men may wrangle about forever without
coming to any conclusion. The theory of the nebular origin of our
planetary system has come to command the assent of all persons qualified
to appreciate the evidence on which it is based; and the more immediate
conclusions which we have drawn from that theory are only such as
are commonly drawn by astronomers and physicists. The doctrine of
an intermolecular and interstellar ether is wrapped up in the
well-established undulatory theory of light. Such is by no means the
case with Sir William Thomson's vortex-atom theory, which to-day is in
somewhat the same condition as the undulatory theory of Huyghens two
centuries ago. This, however, is none the less a hypothesis truly
scientific in conception, and in the speculations to which it leads us
we are still sure of dealing with views that admit at least of definite
expression and treatment. In other words, though our study of the
visible universe has led us to the recognition of a kind of unseen world
underlying the world of things that are seen, yet concerning the economy
of this unseen world we have not been led to entertain any hypothesis
that has not its possible justification in our experiences of visible
phenomena.

We are now called upon, following in the wake of our esteemed authors,
to venture on a different sort of exploration, in which we must cut
loose altogether from our moorings in the world of which we have
definite experience. We are invited to entertain suggestions concerning
the peculiar economy of the invisible portion of the universe which we
have no means of subjecting to any sort of test