VISITS TO THE MOON AND PLANETS
half a space! You will agree with me, I feel sure, that the man who showed them how to draw the whole dial in such circumstances was a remarkably clever man—a wonderful mathematician. His great book, in which he explained the method, his Theoria Motus, is one of those books which are likely to last as long as the world does. The little planet was found again, and to the astonishment of the world, another was also found in the search: and then two more—four burglars when the police had never suspected more than one! However, they were all securely handcuffed and tethered—that is to say, the mathematicians calculated their orbits very carefully, so as to know exactly where to find them when wanted—and the world settled down again after the excitement of the chase. I forgot to tell you that Ceres was first seen on the very first day of the nineteenth century, January 1, 1801; and the other three, Vesta, Pallas and Juno, were all found by March 1807. After that no more were found for forty years, and Hencke, who found the next, had been looking for fifteen years before he found it. Is that not strange when, as we know now, there are hundreds of these little planets in the sky? It shows the difficulties of finding them in the days before photography; since we have been able to take photographs, discovery is much easier; astronomers merely take a photograph of part of the sky, showing all the stars as fixed points, but if one of them seems to have moved or "trailed" during the exposure it is probably a planet.
But we must return to the more important planets, as I feel sure you cannot afford much time to visit