The travelers 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.