in size and
brightness, thus showing beyond a doubt how the Projectile was
moving--in the direction of the luminous point, and _not_ vertically
falling towards the Moon's surface.

"It's a volcano!" cried the Captain, in great excitement; "a volcano in
full blast! An outlet of the Moon's internal fires! Therefore she can't
be a burnt out cinder!"

"It certainly looks like a volcano," replied Barbican, carefully
investigating this new and puzzling phenomenon with his night-glass. "If
it is not one, in fact, what can it be?"

"To maintain combustion," commenced Ardan syllogistically and
sententiously, "air is necessary. An undoubted case of combustion lies
before us. Therefore, this part of the Moon _must_ have an atmosphere!"

"Perhaps so," observed Barbican, "but not necessarily so. The volcano,
by decomposing certain substances, gunpowder for instance, may be able
to furnish its own oxygen, and thus explode in a vacuum. That blaze, in
fact, seems to me to possess the intensity and the blinding glare of
objects burning in pure oxygen. Let us therefore be not over hasty in
jumping at the conclusion of the existence of a lunar atmosphere."

This fire mountain was situated, according to the most plausible
conjecture, somewhere in the neighborhood of the 45th degree, south
latitude, of the Moon's invisible side. For a little while the
travellers indulged the fond hope that they were directly approaching
it, but, to their great disappointment, the path described by the
Projectile lay in a different direction. Its nature therefore they had
no opportunity of ascertaining. It began to disappear behind the dark
horizon within less than half an hour after the time that M'Nicholl had
signalled it. Still, the fact of the uncontested existence of such a
phenomenon was a grand one, and of considerable importance in
selenographic investigations. It proved that heat had not altogether
disappeared from the lunar world; and the existence of heat once
settled, who can say positively that the vegetable kingdom and even the
animal kingdom have not likewise resisted so far every influence tending
to destroy them? If terrestrial astronomers could only be convinced, by
undoubted evidence, of the existence of this active volcano on the
Moon's surface, they would certainly admit of very considerable
modifications in the present doubts regarding her inhabitability.

Thoughts of this kind continued to occupy the minds of our travellers
even