Ireland, and the five largest northern counties of England. It is surrounded by mountains, some being over 11,000 feet high, reckoning from the dark floor.”
I drew their attention to Proclus—a ring-mountain on the eastern side of this sea—which is about eighteen miles in diameter, and the second brightest of the lunar formations. “From its neighbourhood several bright streaks diverge in different directions, two extending a long way across the dark area, and there is a longer one striking towards the north and another towards the south at an angle of about 120 degrees with each other.
“Seen through the telescope, these ray-streaks often appear very brilliant under a high sun, looking in fact very like electric search-lights; though I notice that the Rev. T.W. Webb has rather curiously remarked that these particular streaks are not very easily seen. Similar ray-streaks, many enormously longer than these, are found in various parts of the lunar surface, but their exact nature and origin has never yet been definitely settled. They only come into view when the sun is beginning to be high up in the lunar sky, and the higher the sun, the brighter the rays appear. Some of the shorter ones are ridges, but this is evidently not the case with the others, for they cast no shadows, as ridges would when the sun is low. Very many radiate from a large ring-mountain called Tycho, in the southern hemisphere; and one of them extends, with some breaks, nearly three thousand miles, passing northward over the Sea of Serenity and finally disappearing on the moon’s north-western edge, or ‘limb,’ as it is termed.
“Professor Pickering assumes that these rays were caused by volcanic dust or other light reflecting material emitted from a series of small craters, and states that they are really made up of a series of short rays placed or joined end to end. What I have observed myself seems to bear out this latter statement; but the opinion I have formed as to their origin differs from the theory of Professor Pickering. It seems to me more probable that the volcanic dust was carried by a strong wind, split up into two or more separate currents by a succession of peaks. The wind currents swept clean the area over which they actually passed, but dust fell or drifted in the lines between the currents. Exactly the same thing may be observed in connection with snow-storms on our earth when accompanied by a high wind. One part of the earth’s surface will be swept clean by the wind current, whilst a long line of the adjoining surface is covered with a thick deposit of snow. I have also noticed that where the ray-streaks impinge upon a mountain, or ring, there is an appearance of spreading out and heaping up of the bright material very much as snow would be spread out or drifted up in similar situations on the earth.”
M’Allister here interrupted with the remark that, when we were approaching the moon, he had particularly noticed that all appearance of the face of the “man in the moon” had vanished. He said he had expected to see that more distinctly as we got nearer.
“That would not be the case, M’Allister,” I answered. “The resemblance to a human face which we see from the earth is caused by the combined effect of the bright and dusky areas on the lunar surface as seen from a distance. The depressed dark areas, which we call seas, form the eyes, nose, and mouth of the face, but when we had approached nearer to the moon the details of the surface configuration stood out so much more distinctly that they entirely obliterated the general effect of the markings as seen from a distance.”
“Professor,” exclaimed John, “I have read that before telescopes were invented it was thought by many that the markings seen on the moon were really the features of our own earth reflected by the moon as in a mirror. Is that correct?”
“Oh yes, John,” I said. “It seems to have been a fairly general belief in many parts of the world, and travellers tell us that, even within very recent times, they have found in some of the more out-of-the-way parts of the world that the same idea is still held by uneducated people!”
Objects of interest being so numerous on the lunar surface we could only give a comprehensive glance at many of them, and as we had so many places to inspect, I now gave M’Allister the order to steer eastward.
He accordingly moved his switches and the Areonal quickly passed over the Sea of Tranquillity, which has an area of 140,000 square miles; then over the Sea of Vapours, a smaller area, parts of which have a dusky green tint, from whence to the northward we had a view over the Sea of Serenity, another deep depression nearly as large as the Sea of Tranquillity, and much of which is a light green colour.
Then we came again to the Sea of Showers, a large “sea” having an area of 340,000 square miles; and, still moving eastward, the great lunar “Ocean of Storms” soon came into view. This covers a very large portion of the eastern and north-eastern part of the moon’s surface, and, with all its bays and indentations, is estimated to be two million square miles in extent.
I, however, again reminded them that, although these areas are termed seas and oceans, no water exists there now, whatever may have been the case in the long distant past. They are now only large depressions, and not often level but intersected by hills, ridges, and even mountains.
As we passed along I called their particular attention to the magnificent “Bay of Rainbows” on the north- eastern coast of the Sea of Showers. “From Cape Laplace (9000 feet high) on the western extremity, to Cape Heraclides (4000 feet high) on the eastern extremity, this great bay is about 140 miles across, the depth of its curvature being over eighty miles. It bears a very strong resemblance to many large bays on our sea-coasts in various parts of the world, but I am not aware of any such bay which is bordered by a mass of such lofty mountains as this is.
“We are looking at it now under a high sun, but when the sun has only just risen sufficiently high to illuminate all those high mountains, whilst the lower surroundings are still in shadow, the great bay presents in the telescope the appearance of a brilliant luminous arch springing from the lighted part of the moon and extending far out over the dark part of the disc.
“Farther eastward, and lower down on the Ocean of Storms, you will observe what is admitted by all to be the very brightest large formation upon the moon, viz. Aristarchus—a ring-plain nearly thirty miles in diameter, the floor of which is 5000 feet below the surface level. It possesses a central mountain, very difficult to measure on account of the general brightness, but believed to be about 1300 feet high. Well-defined terraces are seen on the mountain walls enclosing the area, and many external ridges are connected with the walls, especially to the south. This formation is evidently covered with some substance which reflects light to a greater extent than that on similar formations; indeed it appears so bright that when the moon is new and the whole of this part of the disc is dark, Aristarchus can still be seen with a telescope, and this gave rise in the past to the idea that it was a volcano in actual eruption. The explanation is, however, more prosaic, because the mountain is really brought into view by earthshine on its bright covering. When the moon is new the earth is almost fully lighted on the side toward the moon, and sheds a faint light on the dark portion of its disc, thus producing the phenomenon known as ‘the old moon in the new moon’s arms.’
“Close to Aristarchus you will notice another ring-plain, which is called Herodotus, about twenty-three miles in diameter, with a floor 7000 feet depressed; but this formation is not nearly so bright as its neighbour. That high plateau between them is notable on account of the T-shaped cleft in it, which runs into that other long zig-zag cleft (in some parts two miles wide and 1600 feet in depth), whose direction changes abruptly several times in its length of over one hundred miles.
“Turning from this towards the south-west you will see the most majestic formation to be found upon the moon—the great ring-plain called ‘Copernicus,’ after the founder of our present system of astronomy. It is about sixty miles in diameter, only roughly circular in shape, and as it stands isolated upon the great ocean-bed it is most favourably situated for observation. A large number of very high ridges, separated by deep valleys, radiate from it in all directions to a distance of hundreds of miles, presenting the appearance of a grand system of buttresses to the mountain walls. These walls are high, and contain a very large number of peaks which, when seen through the telescope as they catch the sunlight, look like a string of bright pearls shining on the border of the ring. A peak on one side is 12,000 feet in altitude, on the other side is one only 1000 feet lower, whilst, rising from near the central part of the floor, are no less than five small mountain peaks. Owing to its size, brightness, and isolated position, this splendid ring-mountain can be seen from the earth without the aid of a glass; but even a field-glass will reveal much in this and similar formations which cannot be detected by the unaided eye.
“The Rev. T.W. Webb has termed Tycho, in the southern hemisphere, ‘the Metropolitan Crater of the Moon,’ but, in my opinion, Copernicus is, owing to its position and grandeur, much more worthy of that dignity. Tycho is fine in itself, but is not so favourably situated, being surrounded by other formations somewhat in the same way as St. Paul’s Cathedral is surrounded and shut in, for the most part, by other and meaner buildings.
“How much more should we appreciate the splendid proportions and majesty of our Metropolitan Cathedral if we could view it as an isolated building with a fine open space all around it!”
“I quite agree with that, Professor,” remarked John, “and I have always thought it a great pity that Sir Christopher Wren was not allowed to carry out his original plan in this respect.”
