The travellers discussed the origin of these strange rays, but they could not determine their nature any better than terrestrial observers.
"Why," said Nicholl, "may not these rays be simply the spurs of the mountains reflecting the light of the sun more vividly?"
"No," answered Barbicane, "if it were so in certain conditions of the moon they would throw shadows, which they do not."
In fact, these rays only appear when the sun is in opposition with the moon, and they disappear as soon as its rays become oblique.
"But what explanation of these trails of light have been imagined?" asked Michel, "for I cannot believe that savants would ever stop short for want of explanation."
"Yes," answered Barbicane, "Herschel has uttered an opinion, but he does not affirm it."
"Never mind; what is his opinion?"
"He thought that these rays must be streams of cold lava which shone when the sun struck them normally."
"That may be true, but nothing is less certain. However, if we pass nearer to Tycho we shall be in a better position to find out the cause of this radiation."
"What do you think that plain is like, seen from the height we are at?" asked Michel.