at epoch, a few million years ago?

To pretend that our globe must be the only inhabited world because the
others do not resemble it, is to reason, not like a philosopher, but, as
we remarked before, like a fish. Every rational fish ought to assume
that it is impossible to live out of water, since its outlook and its
philosophy do not extend beyond its daily life. There is no answer to
this order of reasoning, except to advise a little wider perception, and
extension of the too narrow horizon of habitual ideas.

For us the resources of Nature may be considered infinite, and
"positive" science, founded upon our senses only, is altogether
inadequate, although it is the only possible basis of our reasoning. We
must learn to see with the eyes of our spirit.

As to the planetary systems other than our own, we are no longer reduced
to hypotheses. We already know with certainty that our Sun is no
exception, as was suggested, and is still maintained, by some theorists.
The discovery in itself is curious enough.

It is surely an exceptional situation that, given a sidereal system
composed of a central sun, and of one or more stars gravitating round
him, the plane of such a system should fall just within our line of
vision, and that it should revolve in such a way that the globes of
which it is composed pass exactly between this sun and ourselves in
turning round him, eclipsing him more or less during this transit. As,
on the other hand, the eclipses would be our only means of determining
the existence of these unknown planets (save indeed from perturbation,
as in the case of Sirius and Procyon), it might have seemed quixotic to
hope for like conditions in order to discover solar systems other than
our own. But these exceptional circumstances have reproduced themselves
at different parts of the Heavens.

Thus, for instance, we have seen that the variable star Algol owes its
variations in brilliancy, which reduce it from second to fourth
magnitude every sixty-nine hours, to the interposition of a body between
itself and the Earth, and celestial mechanics has already been able to
determine accurately the orbit of this body, its dimensions and its
mass, and even the flattening of the sun Algol. Here, then, is a system
in which we know the sun and an enormous planet, whose revolution is
effected in sixty-nine hours with extreme rapidity, as measured by the
spectroscope.

The star [delta] of Cepheus is in the same case: it is an