my dear Captain," here observed Barbican, "have you taken into consideration some of the peculiarities of our Satellite which are decidedly opposed to the development of vegetable and animal existence? Those nights and days, for instance, 354 hours long?"
"I have considered them all," answered the brave Captain. "Days and nights of such an enormous length would at the present time, I grant, give rise to variations in temperature altogether intolerable to any ordinary organization. But things were quite different in the era alluded to. At that time, the atmosphere enveloped the Moon in a gaseous mantle, and the vapors took the shape of clouds. By the screen thus formed by the hand of nature, the heat of the solar rays was tempered and the nocturnal radiation retarded. Light too, as well as heat, could be modified, tempered, and genialized if I may use the expression, by the air. This produced a healthy counterpoise of forces, which, now that the atmosphere has completely disappeared, of course exists no longer. Besides—friend Ardan, you will excuse me for telling you something new, something that will surprise you—"
—"Surprise me, my dear boy, fire away surprising me!" cried Ardan. "I like dearly to be surprised. All I regret is that you scientists have surprised me so much already that I shall never have a good, hearty, genuine surprise again!"
—"I am most firmly convinced," continued the Captain, hardly waiting for Ardan to finish, "that, at the period of the Moon's occupancy by living creatures, her days and nights were by no means 354 hours long."
"Well! if anything could surprise me," said Ardan quickly, "such an assertion as that most certainly would. On what does the honorable gentleman base his most firm conviction?"
"We know," replied the Captain, "that the reason of the Moon's present long day and night is the exact equality of the periods of her rotation on her axis and of her revolution around the Earth. When she has turned once around the Earth, she has turned once around herself. Consequently, her back is turned to the Sun during one-half of the month; and her face during the other half. Now, I don't believe that this state of things existed at the period referred to."
"The gentleman does not believe!" exclaimed Ardan. "The Chair must be excused for reminding the honorable gentleman that it can not accept his incredulity as a sound and valid argument. These two movements have certainly equal periods now; why not always?"
"For the simple reason that this equality of periods is due altogether to the influence of terrestrial attraction," replied the ready Captain. "This attraction at present, I grant, is so great that it actually disables the Moon from revolving on herself; consequently she must always keep the same face turned towards the Earth. But who can assert that this attraction was powerful enough to exert the same influence at the epoch when the Earth herself was only a fluid substance? In fact, who can even assert that the Moon has always been the Earth's satellite?"
"Ah, who indeed?" exclaimed Ardan. "And who can assert that the Moon did not exist long before the Earth was called into being at all? In fact, who can assert that the Earth itself is not a great piece broken off the Moon? Nothing like asking absurd questions! I've often found them passing for the best kind of arguments!"
"Friend Ardan," interposed Barbican, who noticed that the Captain was a little too disconcerted to give a ready reply; "Friend Ardan, I must say you are not quite wrong in showing how certain methods of reasoning, legitimate enough in themselves, may be easily abused by being carried too far. I think, however, that the Captain might maintain his position without having recourse to speculations altogether too gigantic for ordinary intellect. By simply admitting the insufficiency of the primordeal attraction to preserve a perfect balance between the movements of the lunar rotation and revolution, we can easily see how the nights and days could once succeed each other on the Moon exactly as they do at present on the Earth."
"Nothing can be clearer!" resumed the brave Captain, once more rushing to the charge. "Besides, even without this alternation of days and nights, life on the lunar surface was quite possible."
"Of course it was possible," said Ardan; "everything is possible except what contradicts itself. It is possible too that every possibility is a fact; therefore, it is a fact. However," he added, not wishing to press the Captain's weak points too closely, "let all these logical niceties pass for the present. Now that you have established the existence of your humanity in the Moon, the Chair would respectfully ask how it has all so completely disappeared?"
"It disappeared completely thousands, perhaps millions, of years ago," replied the unabashed Captain. "It perished from the physical impossibility of living any longer in a world where the atmosphere had become by degrees too rare to be able to perform its functions as the great resuscitating medium of dependent existences. What took place on the Moon is only what is to take place some day or other on the Earth, when it is sufficiently cooled off."
"Cooled off?"
"Yes," replied the Captain as confidently and with as little hesitation as if he was explaining some of the details of his great machine-shop in Philadelphia; "You see, according as the internal fire near the surface was extinguished or was withdrawn towards the centre, the lunar shell naturally cooled off. The logical consequences, of course, then gradually took place: extinction of organized beings; and then extinction of vegetation. The atmosphere, in the meantime, became thinner and thinner—partly drawn off with the water evaporated by the terrestrial attraction, and partly sinking with the solid water into the crust-cracks caused by cooling. With the disappearance of air capable of respiration, and of water capable of motion, the Moon, of course, became uninhabitable. From that day it became the abode of death, as completely as it is at the present moment."
"That is the fate in store for our Earth?"
"In all probability."
"And when is it to befall us?"
"Just as soon as the crust becomes cold enough to be uninhabitable."
"Perhaps your philosophership has taken the trouble to calculate how many years it will take our unfortunate Terra Mater to cool off?"
"Well; I have."
"And you can rely on your figures?"
"Implicitly."
"Why not tell it at once then to a fellow that's dying of impatience to know all about it? Captain, the Chair considers you one of the most tantalizing creatures in existence!"
"If you only listen, you will hear," replied M'Nicholl quietly. "By careful observations, extended through a series of many years, men have been able to discover the average loss of temperature endured by the Earth in a century. Taking this as the ground work of their calculations, they have ascertained that our Earth shall become an uninhabitable planet in about—"
"Don't cut her life too short! Be merciful!" cried Ardan in a pleading tone half in earnest. "Come, a good long day, your Honor! A good long day!"
"The planet that we call the Earth," continued the Captain, as grave as a judge, "will become uninhabitable to human beings, after a lapse of 400 thousand years from the present time."
"Hurrah!" cried Ardan, much relieved. "Vive la Science! Henceforward, what miscreant will persist in saying that the Savants are good for nothing? Proudly pointing to this calculation, can't they exclaim to all defamers: 'Silence, croakers! Our services are invaluable! Haven't we insured the Earth for 400 thousand years?' Again I say vive la Science!"
"Ardan," began the Captain with some asperity, "the foundations on which Science has raised—"
"I'm half converted already,"
