"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.