Inaccessible and marvellously extended over this ground of picturesque relief! Nature had not left the bottom of this crater flat and empty. It possessed a special orography, a mountain system which made it a world apart. The travellers clearly distinguished the cones, central hills, remarkable movements of the ground, naturally disposed for the reception of masterpieces of Selenite architecture. There was the place for a temple, here for a forum, there the foundations of a palace, there the plateau of a citadel, the whole overlooked by a central mountain 1,500 feet high--a vast circuit which would have held ancient Rome ten times over. "Ah!" exclaimed Michel Ardan, made enthusiastic by the sight, "what grand towns could be built in this circle of mountains! A tranquil city, a peaceful refuge, away from all human cares! How all misanthropes could live there, all haters of humanity, all those disgusted with social life!" "All! It would be too small for them!" replied Barbicane simply. CHAPTER XVIII. GRAVE QUESTIONS. In the meantime the projectile had passed the neighbourhood of Tycho. Barbicane and his two friends then observed, with the most scrupulous attention, those brilliant radii which the celebrated mountain disperses so curiously on every horizon. What was this radiating aureole? What geological phenomenon had caused those ardent beams? This question justly occupied Barbicane. Under his eyes, in every direction, ran luminous furrows, with raised banks and concave middle, some ten miles, others more than twenty miles wide. These shining trails ran in certain places at least 300 leagues from Tycho, and seemed to cover, especially towards the east, north-east, and north, half the southern hemisphere. One of these furrows stretched as far as the amphitheatre of Neander, situated on the 40th meridian. Another went rounding off through the Sea of Nectar and broke against the chain of the Pyrenees after a run of 400 leagues; others towards the west covered with a luminous network the Sea of Clouds and the Sea of Humours. What was the origin of these shining rays running equally over plains and reliefs, however high? They all started from a common centre, the crater of Tycho. They emanated from it. Herschel attributed their brilliant aspect to ancient streams of lava congealed by the cold, an opinion which has not been generally received. Other astronomers have seen in these inexplicable rays a kind of _moraines_, ranges of erratic blocks thrown out at the epoch of the formation of Tycho. "And why should it not be so?" asked Nicholl of Barbicane, who rejected these different opinions at the same time that he related them. "Because the regularity of these luminous lines, and the violence necessary to send them to such a distance, are inexplicable. "_Par bleu_!" replied Michel Ardan. "I can easily explain to myself the origin of these rays." "Indeed," said Barbicane.