cold that a further encroachment on their little stock of gas could be put off no longer. The light, of course, they could manage to do without; but a little heat was absolutely necessary to prevent them from freezing to death. Fortunately, however, the caloric developed by the Reiset and Regnault process for purifying the air, raised the internal temperature of the Projectile a little, so that, with an expenditure of gas much less than they had expected, our travellers were able to maintain it at a degree capable of sustaining human life.
By this time, also, all observations through the windows had become exceedingly difficult. The internal moisture condensed so thick and congealed so hard on the glass that nothing short of continued friction could keep up its transparency. But this friction, however laborious they might regard it at other times, they thought very little of just now, when observation had become far more interesting and important than ever.
If the Moon had any atmosphere, our travellers were near enough now to strike any meteor that might be rushing through it. If the Projectile itself were floating in it, as was possible, would not such a good conductor of sound convey to their ears the reflexion of some lunar echo, the roar of some storm raging among the mountains, the rattling of some plunging avalanche, or the detonations of some eructating volcano? And suppose some lunar Etna or Vesuvius was flashing out its fires, was it not even possible that their eye could catch a glimpse of the lurid gleam? One or two facts of this kind, well attested, would singularly elucidate the vexatious question of a lunar atmosphere, which is still so far from being decided. Full of such thoughts and intensely interested in them, Barbican, M'Nicholl and Ardan, patient as astronomers at a transit of Venus, watched steadily at their windows, and allowed nothing worth noticing to escape their searching gaze.
Ardan's patience first gave out. He showed it by an observation natural enough, for that matter, to a mind unaccustomed to long stretches of careful thought:
"This darkness is absolutely killing! If we ever take this trip again, it must be about the time of the New Moon!"
"There I agree with you, Ardan," observed the Captain. "That would be just the time to start. The Moon herself, I grant, would be lost in the solar rays and therefore invisible all the time of our trip, but in compensation, we should have the Full Earth in full view. Besides—and this is your chief point, no doubt, Ardan—if we should happen to be drawn round the Moon, just as we are at the present moment, we should enjoy the inestimable advantage of beholding her invisible side magnificently illuminated!"
"My idea exactly, Captain," said Ardan. "What is your opinion on this point, Barbican?"
"My opinion is as follows:" answered Barbican, gravely. "If we ever repeat this journey, we shall start precisely at the same time and under precisely the same circumstances. You forget that our only object is to reach the Moon. Now suppose we had really landed there, as we expected to do yesterday, would it not have been much more agreeable to behold the lunar continents enjoying the full light of day than to find them plunged in the dismal obscurity of night? Would not our first installation of discovery have been under circumstances decidedly extremely favorable? Your silence shows that you agree with me. As to the invisible side, once landed, we should have the power to visit it when we pleased, and therefore we could always choose whatever time would best suit our purpose. Therefore, if we wanted to land in the Moon, the period of the Full Moon was the best period to select. The period was well chosen, the time was well calculated, the force was well applied, the Projectile was well aimed, but missing our way spoiled everything."
"That's sound logic, no doubt," said Ardan; "still I can't help thinking that all for want of a little light we are losing, probably forever, a splendid opportunity of seeing the Moon's invisible side. How about the other planets, Barbican? Do you think that their inhabitants are as ignorant regarding their satellites as we are regarding ours?"
"On that subject," observed M'Nicholl, "I could venture an answer myself, though, of course, without pretending to speak dogmatically on any such open question. The satellites of the other planets, by their comparative proximity, must be much easier to study than our Moon. The Saturnians, the Uranians, the Jovians, cannot have had very serious difficulty in effecting some communication with their satellites. Jupiter's four moons, for instance, though on an average actually 2-1/2 times farther from their planet's centre than the Moon is from us, are comparatively four times nearer to him on account of his radius being eleven times greater than the Earth's. With Saturn's eight moons, the case is almost precisely similar. Their average distance is nearly three times greater than that of our Moon; but as Saturn's diameter is about 9 times greater than the Earth's, his bodyguards are really between 3 and 4 times nearer to their principal than ours is to us. As to Uranus, his first satellite, Ariel, half as far from him as our Moon is from the Earth, is comparatively, though not actually, eight times nearer."
"Therefore," said Barbican, now taking up the subject, "an experiment analogous to ours, starting from either of these three planets, would have encountered fewer difficulties. But the whole question resolves itself into this. If the Jovians and the rest have been able to quit their planets, they have probably succeeded in discovering the invisible sides of their satellites. But if they have not been able to do so, why, they're not a bit wiser than ourselves—But what's the matter with the Projectile? It's certainly shifting!"
Shifting it certainly was. While the path it described as it swung blindly through the darkness, could not be laid down by any chart for want of a starting point, Barbican and his companions soon became aware of a decided modification of its relative position with regard to the Moon's surface. Instead of its side, as heretofore, it now presented its base to the Moon's disc, and its axis had become rigidly vertical to the lunar horizon. Of this new feature in their journey, Barbican had assured himself by the most undoubted proof towards four o'clock in the morning. What was the cause? Gravity, of course. The heavier portion of the Projectile gravitated towards the Moon's centre exactly as if they were falling towards her surface.
But were they falling? Were they at last, contrary to all expectations, about to reach the goal that they had been so ardently wishing for? No! A sight-point, just discovered by M'Nicholl, very soon convinced Barbican that the Projectile was as far as ever from approaching the Moon, but was moving around it in a curve pretty near concentric.
M'Nicholl's discovery, a luminous gleam flickering on the distant verge of the black disc, at once engrossed the complete attention of our travellers and set them to divining its course. It could not possibly be confounded with a star. Its glare was reddish, like that of a distant furnace on a dark night; it kept steadily increasing 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
