"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."