He knew that they were a kind of furrow found on every part of the disc which was not mountainous; that these furrows, generally isolated, measured from 400 to 500 leagues in length; that their breadth varied from 1,000 to 1,500 yards, and that their borders were strictly parallel; but he knew nothing more either of their formation or their nature.
Barbicane, through his glasses, observed these rifts with great attention. He noticed that their borders were formed of steep declivities; they were long parallel ramparts, and with some small amount of imagination he might have admitted the existence of long lines of fortifications, raised by Selenite engineers. Of these different rifts some were perfectly straight, as if cut by a line; others were slightly curved, though still keeping their borders parallel; some crossed each other, some cut through craters; here they wound through ordinary cavities, such as Posidonius or Petavius; there they wound through the seas, such as the "Sea of Serenity."
These natural accidents naturally excited the imaginations of these terrestrial astronomers. The first observations had not discovered these rifts. Neither Hevelius, Cassin, La Hire, nor Herschel seemed to have known them. It was Schroeter who in 1789 first drew attention to them. Others followed who studied them, as Pastorff, Gruithuysen, Boeer, and Moedler. At this time their number amounts to seventy; but, if they have been counted, their nature has not yet been determined; they are certainly not fortifications, any more than they are the ancient beds of dried-up rivers; for, on one side, the waters, so slight on the moon's surface, could never have worn such drains for themselves; and, on the other, they often cross craters of great elevation.
We must, however, allow that Michel Ardan had "an idea," and that, without knowing it, he coincided in that respect with Julius Schmidt.
"Why," said he, "should not these unaccountable appearances be simply phenomena of vegetation?"
"What do you mean?" asked Barbicane quickly.
"Do not excite yourself, my worthy president," replied Michel; "might it not be possible that the dark lines forming that bastion were rows of trees regularly placed?"
"You stick to your vegetation, then?" said Barbicane.
"I like," retorted Michel Ardan, "to explain what you savants cannot explain; at least my hypotheses has the advantage of indicating why these rifts disappear, or seem to disappear, at certain seasons."
"And for what reason?"
"For the reason that the trees become invisible when they lose their leaves, and visible again when they regain them."
"Your explanation is ingenious, my dear companion," replied Barbicane, "but inadmissible."
"Because, so to speak, there are no seasons on the moon's surface, and that, consequently, the phenomena of vegetation of which you speak cannot occur."
Indeed, the slight obliquity of the lunar axis keeps the sun at an almost equal height in every latitude. Above the equatorial regions the radiant orb almost invariably occupies the zenith, and does not pass the limits of the horizon in the polar regions; thus, according to each region, there reigns a perpetual winter, spring, summer, or autumn, as in the planet Jupiter, whose axis is but little inclined upon its orbit.
What origin do they attribute to these rifts? That is a question difficult to solve. They are certainly anterior to the formation of craters and circles, for several have introduced themselves by breaking through their circular ramparts. Thus it may be that, contemporary with the later geological epochs, they are due to the expansion of natural forces.
But the projectile had now attained the fortieth degree of lunar latitude, at a distance not exceeding 40 miles. Through the glasses objects appeared to be only four miles distant.
At this point, under their feet, rose Mount Helicon, 1,520 feet high, and round about the left rose moderate elevations, enclosing a small portion of the "Sea of Rains," under the name of the Gulf of Iris.