an experiment
analogous to that of President Barbicane would have presented less
difficulties. If, therefore, their inhabitants have attempted the
enterprise, they have, perhaps, acquainted themselves with the
constitution of the half of the disc which their satellite hides
eternally from their eyes. But if they have never left their planet,
they do not know more about them than the astronomers of the earth.

In the meantime the bullet was describing in the darkness that
incalculable trajectory which no landmark allowed them to find out. Was
its direction altered either under the influence of lunar attraction or
under the action of some unknown orb? Barbicane could not tell. But a
change had taken place in the relative position of the vehicle, and
Barbicane became aware of it about 4 a.m.

The change consisted in this, that the bottom of the projectile was
turned towards the surface of the moon, and kept itself perpendicular
with its axis. The attraction or gravitation had caused this
modification. The heaviest part of the bullet inclined towards the
invisible disc exactly as if it had fallen towards it.

Was it falling then? Were the travellers at last about to reach their
desired goal? No. And the observation of one landmark, inexplicable in
itself, demonstrated to Barbicane that his projectile was not nearing
the moon, and that it was following an almost concentric curve.

This was a flash of light which Nicholl signalised all at once on the
limit of the horizon formed by the black disc. This point could not be
mistaken for a star. It was a reddish flame, which grew gradually
larger--an incontestable proof that the projectile was getting nearer
it, and not falling normally upon the surface of the satellite.

"A volcano! It is a volcano in activity!" exclaimed Nicholl--"an
eruption of the interior fires of the moon. That world, then, is not
quite extinguished."

"Yes, an eruption!" answered Barbicane, who studied the phenomenon
carefully through his night-glass. "What should it be if not a volcano?"

"But then," said Michel Ardan, "air is necessary to feed that
combustion, therefore there is some atmosphere on that part of the
moon."

"Perhaps so," answered Barbicane, "but not necessarily. A volcano, by
the decomposition of certain matters, can furnish itself with oxygen,
and so throw up flames into the void. It seems to me, too, that that
deflagration has the intensity and brilliancy of objects the combusti