At this moment the projectile hung perpendicularly over the circle. The circumference of Copernicus formed almost a perfect circle, and its steep escarpments were clearly defined. They could even distinguish a second ringed enclosure. Around spread a greyish plain, of a wild aspect, on which every relief was marked in yellow. At the bottom of the circle, as if enclosed in a jewel case, sparkled for one instant two or three eruptive cones, like enormous dazzling gems. Towards the north the escarpments were lowered by a depression which would probably have given access to the interior of the crater. In passing over the surrounding plains, Barbicane noticed a great number of less important mountains; and among others a little ringed one called Guy Lussac, the breadth of which measured twelve miles. Towards the south, the plain was very flat, without one elevation, without one projection. Towards the north, on the contrary, till where it was bounded by the Sea of Storms it resembled a liquid surface agitated by a storm, of which the hills and hollows formed a succession of waves suddenly congealed. Over the whole of this, and in all directions, lay the luminous lines, all converging to the summit of Copernicus. The travellers discussed the origin of these strange rays; but they could not determine their nature any more than terrestrial observers. "But why," said Nicholl, "should not these rays be simply spurs of mountains which reflect more vividly the light of the sun?" "No," replied Barbicane; "if it was so, under certain conditions of the moon, these ridges would cast shadows, and they do not cast any." And indeed, these rays only appeared when the orb of day was in opposition to the moon, and disappeared as soon as its rays became oblique. "But how have they endeavoured to explain these lines of light?" asked Michel; "for I cannot believe that savants would ever be stranded for want of an explanation." "Yes," replied Barbicane; "Herschel has put forward an opinion, but he did not venture to affirm it." "Never mind. What was the opinion?" "He thought that these rays might be streams of cooled lava which shone when the sun beat straight upon them. It may be so; but nothing can be less certain. Besides, if we pass nearer to Tycho, we shall be in a better position to find out the cause of this radiation." Illustration: "THIS PLAIN WOULD THEN BE NOTHING BUT AN IMMENSE CEMETERY." "Do you know, my friends, what that plain, seen from the height we are at, resembles?" said Michel. "No," replied Nicholl. "Very well; with all those pieces of lava lengthened like rockets, it resembles an immense game of spelikans thrown pell-mell. There wants but the hook to pull them out one by one." "Do be serious," said Barbicane.