Passing on towards the south-west, we had a long look at the magnificent formation named Tycho. It is a ring-plain nearly fifty-six miles in diameter, the mountain walls having some peaks over 17,000 feet in height. I drew their attention to the long bright ray-streaks which radiate in all directions for many hundreds of miles from the neighbourhood of this formation, to which I alluded when we had been looking at the rays from Proclus. Tycho and these bright streaks can be seen from the earth when the moon is full without the aid of a telescope, if one possesses good eyesight.
An enormous number of ring-plains and ring-mountains exists all over the southern half of the moon's disc; in many cases there are rings within rings, and others where they have overlapped or cut into previously formed rings.
Moving almost due south, we passed the large but partially ruined walled plain known as Maginus. This ring has a floor which is no less than 14,000 feet below the lunar surface. We then arrived at that favourite object for telescopic observers which is named Clavius. This is an enormous ring-plain, being over 142 miles in diameter, and encloses an area of 16,000 square miles, thus being half the area of Scotland. It has a very depressed floor, and some of the mountains are 16,000 to 17,000 feet in altitude.
Farther on, and close to the south pole, we saw the very deepest of the lunar walled plains, which is named after Newton, who possessed probably the deepest intellect of any of our astronomers. A smaller formation south of Plato was originally named after him, but was not considered worthy of a man of his scientific eminence, so the name was transferred to the formation we were looking upon. It is about 143 miles long and very irregular in shape, and its depth is about 24,000 feet—so deep, in fact, that the sun's light never reaches to the bottom; thus, when we look at it from the earth, the floor is always in shadow.
The Leibnitz Mountains, unfortunately, were not visible, as the sun had set upon them. I, however, mentioned that this range comprises several peaks which are believed to be the highest on the lunar surface, reaching as they do an altitude of 30,000 feet, and, according to some measurements, 40,000 feet. They are very difficult to measure, owing to the fact that they are really situated on the farther side of the moon, extending east and west of the south pole, and are only occasionally brought into view by the moon's libration; even then they are seen in profile, and so situated that they cannot be measured with certainty. They are, however, so high that they blunt the southern cusp of the moon when it is in crescent form.
I now directed M'Allister to turn the vessel in a north-easterly direction, and we moved across to the last objects which I proposed to examine. One was the large walled plain "Schickard"—about 135 miles in diameter—which encloses several other rings; the other, which lies to the south-east of it and close to the moon's south-eastern limb, is probably the most unique object on the lunar surface. As we gazed upon it I explained that the formation, which is known as "Wargentin," would probably in the usual course of events have been a ring-plain about fifty-four miles in diameter, but it really is a high plateau of that size, with very low ramparts. It is evidently a ring-plain which became filled to the brim with lava, or mud, that welled up from the interior of the moon; and the mountain walls, being exceptionally strong and without any breaks or gaps, withstood the enormous pressure of the lava, which therefore solidified and formed the great plateau as we now see it. The low ramparts, which we noticed here and there, are really the isolated peaks and ridges of the mountains forming the walls. This is the only known instance of such a formation; but probably others would exist had not the walls of the rings given way under the pressure of the lava. The walls of several ring-plains have been quite carried away, and, in some cases so obliterated, that it is now difficult to make out the original shape of the rings.
Having taken a last look at this unique object, I directed M'Allister to set the machinery in motion and rise for the purpose of quitting the moon.
"But," interposed John, "are you not going to have a look at the back of the moon, Professor?"
"No, John," I answered, "only a small portion of it is now in the sunlight, the rest is in the blackest darkness, so we should not be likely to learn much more about it than we know at present."
"Do you think the moon is inhabited?" he then asked.