Newcomb in his excellent "Popular Astronomy," that there has been no actual change in the crater. I must indeed remark that, after comparing several drawings of the same regions by Schroeter, Maedler, Lohrman, and Schmidt, with each other and with the moon's surface, I find myself by no means very strongly impressed by the artistic skill of any of these observers. I scarcely know a single region in the moon where change might not be inferred to have taken place if any one of the above-named observers could be implicitly relied upon. As, fortunately, their views differ even more widely _inter se_ than from the moon's own surface, we are not driven to so startling a conclusion. However, if we assume even that Linne has undergone change, we still have no reason to believe that the change is volcanic. A steep wall, say half a mile in height, surrounding a crater four or five miles in diameter, no longer stands at this height above the enclosed space, if the believers in a real change are to be trusted. But, as Dr. Huggins well remarked long ago, if volcanic forces competent to produce disturbance of this kind are at work in the moon, we ought more frequently to recognize signs of change, for they could scarcely be at work in one part only of the moon's surface, or only at long intervals of time. It is so easy to explain the overthrow of such a wall as surrounded Linne (always assuming we can rely upon former accounts) without imagining volcanic action, that, considering the overwhelming weight of _a priori_ probability against such action at the present time, it would be very rash to adopt the volcanic theory. The expansions and contractions described above would not only be able to throw down walls of the kind, but they would be sure to do so from time to time. Indeed, as a mere matter of probabilities, it may be truly said that it would be exceedingly unlikely that catastrophes such as the one which may have occurred in this case would fail to happen at comparatively short intervals of time. It would be so unlikely, that I am almost disposed to adopt the theory that there really has been a change in Linne, for the reason that on that theory we get rid of the difficulty arising from the apparent fixity of even the steepest lunar rocks. However, after all, the time during which men have studied the moon with the telescope--only two hundred and sixty-nine years--is a mere instant compared with the long periods during which the moon has been exposed to the sun's intense heat by day and a more than arctic intensity of cold by night. It may well be that, though lunar landslips occur at short intervals of time, these intervals are only short when compared with those periods, hundreds of millions of years long, of which we had to speak a little while ago. Perhaps in a period of ten or twenty thousand years we might have a fair chance of noting the occurrence of one or two catastrophes of the kind,