“A fine country truly!” said Nicholl.

“Never mind!  I should like to be there already!  It will be comical to have the earth for a moon, to see it rise on the horizon, to recognise the configuration of its continents, to say to oneself, ’There’s America and there’s Europe;’ then to follow it till it is lost in the rays of the sun!  By-the-bye, Barbicane, have the Selenites any eclipses?”

“Yes, eclipses of the sun,” answered Barbicane, “when the centres of the three stars are on the same line with the earth in the middle.  But they are merely annular eclipses, during which the earth, thrown like a screen across the solar disc, allows the greater part to be seen.”

“Why is there no total eclipse?” asked Nicholl.  “Is it because the cone of shade thrown by the earth does not extend beyond the moon?”

“Yes, if you do not take into account the refraction produced by the terrestrial atmosphere, not if you do take that refraction into account.  Thus, let delta be the horizontal parallax and p the apparent semidiameter—­”

“Ouf!” said Michel, “half of v zero square!  Do speak the vulgar tongue, man of algebra!”

“Well, then, in popular language,” answered Barbicane, “the mean distance between the moon and the earth being sixty terrestrial radii, the length of the cone of shadow, by dint of refraction, is reduced to less than forty-two radii.  It follows, therefore, that during the eclipses the moon is beyond the cone of pure shade, and the sun sends it not only rays from its edges, but also rays from its centre.”

“Then,” said Michel in a grumbling tone, “why is there any eclipse when there ought to be none?”

“Solely because the solar rays are weakened by the refraction, and the atmosphere which they traverse extinguishes the greater part of them.”

“That reason satisfies me,” answered Michel; “besides, we shall see for ourselves when we get there.  Now, Barbicane, do you believe that the moon is an ancient comet?”

“What an idea!”

“Yes,” replied Michel, with amiable conceit, “I have a few ideas of that kind.”

“But that idea does not originate with Michel,” answered Nicholl.

“Then I am only a plagiarist.”

“Without doubt,” answered Nicholl.  “According to the testimony of the ancients, the Arcadians pretended that their ancestors inhabited the earth before the moon became her satellite.  Starting from this fact, certain savants think the moon was a comet which its orbit one day brought near enough to the earth to be retained by terrestrial attraction.”

“And what truth is there in that hypothesis?” asked Michel.

“None,” answered Barbicane, “and the proof is that the moon has not kept a trace of the gaseous envelope that always accompanies comets.”

“But,” said Nicholl, “might not the moon, before becoming the earth’s satellite, have passed near enough to the sun to leave all her gaseous substances by evaporation?”