We will suppose that our planet is without a satellite. The nights are brilliant or starless, as the clouds may determine, but in all the measureless reaches of space is no world having a visible disk, with vicissitudes of light and shadow. One day a famous man of science announces in the public prints a startling discovery. He has found an orb, smaller than the earth but of considerable magnitude, moving in such a direction and at such a rate of speed that at a stated time the next year it will have approached our sphere so closely as to be caught by its attractive power and held, a prisoner, wheeling round and round in a vain endeavor to escape. He goes on to explain that the invisible tether will be, astronomically speaking, but a stone’s throw in length: the captive world will have in fact the astonishing propinquity of only a quarter of a million miles! We shall be able to see, even with unassisted eyes, the very mountains and valleys upon its surface, while a glass of moderate power will show, not only these mountains (many times higher than those of our own orb) with perfect definition, their long black shadows projected upon the plains, but will reveal the details of extinct craters wide enough to engulf a terrestrial province, and how deep Heaven knows. Upon this strange new world, the great man goes on to say, we shall be able to observe the mutations of its day and night, tracing the lines of its dawn and sunset exactly as, if we were there, we could observe the more rapid changes upon the body of our own planet; and surely it would be worth something to stand away from our spinning orb and take in all its visible vicissitudes in one comprehensive view.