"In the actual state of the moon," resumed Barbicane, "the long nights and days create differences of temperature insupportable to the constitution, but it was not so at that epoch of historical times. The atmosphere enveloped the disc with a fluid mantle. Vapour deposited itself in the form of clouds. This natural screen tempered the ardour of the solar lays, and retained the nocturnal radiation. Both light and heat could diffuse themselves in the air. Hence there was equilibrium between the influences which no longer exists now that the atmosphere has almost entirely disappeared. Besides, I shall astonish you—"
"Astonish us?" said Michel Ardan.
"But I believe that at the epoch when the moon was inhabited the nights and days did not last 354 hours!"
"Why so?" asked Nicholl quickly.
"Because it is very probable that then the moon's movement of rotation on her axis was not equal to her movement of revolution, an equality which puts every point of the lunar disc under the action of the solar rays for fifteen days."
"Agreed," answered Nicholl; "but why should not these movements have been equal, since they are so actually?"
"Because that equality has only been determined by terrestrial attraction. Now, how do we know that this attraction was powerful enough to influence the movements of the moon at the epoch the earth was still fluid?"
"True," replied Nicholl; "and who can say that the moon has always been the earth's satellite?"
"And who can say," exclaimed Michel Ardan, "that the moon did not exist before the earth?"
Imagination began to wander in the indefinite field of hypotheses.
Barbicane wished to hold them in.