Etna, Cotopaxi, and Popocatepetl carry their craters, could not stand even on the moon. Observe the generally radial arrangement of the lines about Copernicus, recalling the similar arrangement of lava flows about terrestrial volcanoes. Some of these lines, as you will see, consist of long rows of pits. Similar phenomena may be seen along the lava streams that we are familiar with on our planet, where small craters break forth one after another. A striking example of this arrangement is visible in the photograph on the northeastern slope leading up toward the Copernicus ring. But you will also see many very remarkable rows of pits in the vicinity of Copernicus which are not radial in arrangement with respect to the ring. The most conspicuous of these is on the northwestern side, about half way between Copernicus and the ring of Eratosthenes, which standing at the upper end of the chain of the Apennines appears at the left-hand edge of the picture. There are hundreds, probably thousands, of these pits on all sides of Copernicus. “One of the explanations that has been suggested for them is that they were produced by the fall of enormous volcanic bombs thrown from Copernicus when it was in eruption. I wish merely to mention this idea without comment. It however calls up another interesting theory, which has not met with much acceptance, to the effect that such lunar volcanoes as Copernicus may have been powerful enough to eject masses of lava and rocks with a velocity sufficient to enable them to escape from the attraction of the moon, whereupon they became meteorites traveling in independent orbits around the sun. Some of these, the theory suggests, may be among those that have fallen upon the earth. A velocity of a mile and a half per second would be sufficient to overcome the gravitation of the moon. That is only three or four times the initial velocity which some modern guns are capable of imparting to their projectiles.” “I am sorry,” explained my friend, “that you seem to attach little importance to so interesting a theory. It stirs my imagination to think of the moon sending bits of herself back to her mother planet. For my part, the theory does not seem to be any harder to believe than that of your Professor Darwin that the whole moon was thrown off from the earth. Besides, it intensifies my appreciation of the grandeur of Copernicus when I am told that that great volcano could once bombard the earth across—what is it, 240,000 miles?—of space.”