What would be the mental effects of perpetual night upon a race of intelligent creatures doomed to that condition? Perhaps not quite so grievous as we are apt to think. The constellations in all their splendor would circle before their eyes with the revolution of their planet about the sun, and with the exception of the sun itself--which they could see by making a journey to the opposite hemisphere--all the members of the solar system would pass in succession through their mid-heaven, and two of them would present themselves with a magnificence of planetary display unknown on the earth. Venus, when in opposition under the most favorable circumstances, is scarcely more than 24,000,000 miles from Mercury, and, showing herself at such times with a fully illuminated disk--as, owing to her position within the orbit of the earth, she never can do when at her least distance from us--she must be a phenomenon of unparalleled beauty, at least four times brighter than we ever see her, and capable, of course, of casting a strong shadow. The earth, also, is a splendid star in the midnight sky of Mercury, and the moon may be visible to the naked eye as a little attendant circling about its brilliant master. The outer planets are slightly less conspicuous than they are to us, owing to increase of distance. The revolution of the heavens as seen from the night side of Mercury is quite different in period from that which we are accustomed to, although the apparent motion is in the same direction, viz., from east to west. The same constellations remain above the horizon for weeks at a time, slowly moving westward, with the planets drifting yet more slowly, but at different rates, among them; the nearer planets, Venus and the earth, showing the most decided tendency to loiter behind the stars. On the side where eternal sunlight shines the sky of Mercury contains no stars. Forever the pitiless blaze of day; forever, "All in a hot and copper sky The bloody sun at noon." As it is difficult to understand how water can exist on the night hemisphere, except in the shape of perpetual snow and ice, so it is hard to imagine that on the day hemisphere water can ever be precipitated from the vaporous form. In truth, there can be very little water on Mercury even in the form of vapor, else the spectroscope would have given unquestionable evidence of its presence. Those who think that Mercury is entirely waterless and almost, if not quite, airless may be right. In these respects it would then resemble the moon, and, according to some observers, it possesses another characteristic lunar feature in the roughening of its surface by what seem to be innumerable volcanic craters.