It was Schroeter, in 1789, who called the attention of scientists to them for the first time. He had only 11 to show, but Lohrmann soon recorded 75 more. Pastorff, Gruithuysen, and particularly Beer and Maedler were still more successful, but Julius Schmidt, the famous astronomer of Athens, has raised their number up to 425, and has even published their names in a catalogue. But counting them is one thing, determining their nature is another. They are not fortifications, certainly: and cannot be ancient beds of dried up rivers, for two very good and sufficient reasons: first, water, even under the most favorable circumstances on the Moon's surface, could have never ploughed up such vast channels; secondly, these chasms often traverse lofty craters through and through, like an immense railroad cutting. At these details, Ardan's imagination became unusually excited and of course it was not without some result. It even happened that he hit on an idea that had already suggested itself to Schmidt of Athens. "Why not consider them," he asked, "to be the simple phenomena of vegetation?" "What do you mean?" asked Barbican. "Rows of sugar cane?" suggested M'Nicholl with a snicker. "Not exactly, my worthy Captain," answered Ardan quietly, "though you were perhaps nearer to the mark than you expected. I don't mean exactly rows of sugar cane, but I do mean vast avenues of trees--poplars, for instance--planted regularly on each side of a great high road." "Still harping on vegetation!" said the Captain. "Ardan, what a splendid historian was spoiled in you! The less you know about your facts, the readier you are to account for them." "_Ma foi_," said Ardan simply, "I do only what the greatest of your scientific men do--that is, guess. There is this difference however between us--I call my guesses, guesses, mere conjecture;--they dignify theirs as profound theories or as astounding discoveries!" "Often the case, friend Ardan, too often the case," said Barbican. "In the question under consideration, however," continued the Frenchman, "my conjecture has this advantage over some others: it explains why these rills appear and seem to disappear at regular intervals." "Let us hear the explanation," said the Captain. "They become invisible when the trees lose their leaves, and they reappear when they resume them." "His explanation is not without ingenuity," observed Barbican to M'Nicholl, "but, my dear friend," turning to Ardan, "it is hardly admissible." "Probably not," said Ardan, "but why not?" "Because as the Sun is nearly always vertical to the lunar equator, the Moon can have no change of seasons worth mentioning; therefore her vegetation can present none of the phenomena that you speak of."