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 combustion of which is produced in pure oxygen.  We must not be in a hurry to affirm the existence of a lunar atmosphere.”

The burning mountain was situated at the 45th degree of south latitude on the invisible part of the disc.  But to the great disappointment of Barbicane the curve that the projectile described dragged it away from the point signalised by the eruption, therefore he could not exactly determine its nature.  Half-an-hour after it had first been seen this luminous point disappeared on the horizon.  Still the authentication of this phenomenon was a considerable fact in selenographic studies.  It proved that all heat had not yet disappeared from the interior of this globe, and where heat exists, who may affirm that the vegetable kingdom, or even the animal kingdom itself, has not until now resisted the destructive influences?  The existence of this volcano in eruption, indisputably established by earthly savants, was favourable to the theory of the habitability of the moon.

Barbicane became absorbed in reflection.  He forgot himself in a mute reverie, filled with the mysterious destinies of the lunar world.  He was trying to connect the facts observed up till then, when a fresh incident recalled him suddenly to the reality.

This incident was more than a cosmic phenomenon; it was a threatening danger, the consequences of which might be disastrous.

Suddenly in the midst of the ether, in the profound darkness, an enormous mass had appeared.  It was like a moon, but a burning moon of almost unbearable brilliancy, outlined as it was on the total obscurity of space.  This mass, of a circular form, threw such light that it filled the projectile.  The faces of Barbicane, Nicholl, and Michel Ardan, bathed in its white waves, looked spectral, livid, blafard, like the appearance produced by the artificial light of alcohol impregnated with salt.