Well, I am glad it is here now for me. Will there be time for my London cousins to catch a glance at it when it wanders northward again? O no, no; it does not move quite so fast as that. But if Abraham had been sojourning in southern Europe, instead of Asia, he could have seen it, though it was then making its way back to the south. How could the Cross slip away from the other southern stars to go on such migrations? Not so. All the stars keep their places relatively to each other, as you see them do in the nightly progress from east to west. In the daily motion none get before the other, nor did the Cross get before its neighbours. Well, I am fairly done. That is a riddle. Look at the question, boy. What makes the apparent daily motion of the stars? The real daily motion of the earth. And if, then, you observe any other peculiarity of movement among your bright friends up there, to what may you reasonably ascribe it? I should imagine some peculiar twist, roll, or slipping of this world of ours. True. And if there be seen among the polar stars, north as well as south, a slight but regular movement, a sort of a swing round, so that some stars get farther off the spot we call the south pole of the heavens, while others approached it nearer, and yet so swung round that at last all find their old places again, how could you get a motion of the earth to make up for all that? Ah! I must contrive that the world should do three things. It must roll over once a day, roll round the sun once a year, and yet wriggle about in another way at the same time.--Stop a bit--I have it. My top turns round itself, and pretty quickly, too; it shifts about on the floor almost in a circle as it turns round; and I see it, especially when it is quietly spinning, have a slow roll of the head, like a sailor when walking ashore, as if its head were a little giddy. You have hit it exactly, my good fellow. The three motions of your top are much like the three motions of the world. That top-heavy slow swinging of your top while it is spinning in full force is like a sort of head-rolling of the earth. The poles seem to have a roll of their own, independent of the regular roll. Yes; and that would make the Polar stars seem as though they were swinging. But how long are they before they are in their regular places again? Astronomers calculate 25,850 years. But will not this changing make the star-charts of the ancients all wrong? Indeed it does. Aries the Ram, for instance, as a _sign_, is the first thirty degrees on the celestial globe; but as a _constellation_ it has shifted to between the thirtieth and sixtieth degree on the ecliptic. This is called the precession of the Equinoxes. How is that? I know when the equinoxes are--March 21st and September 23rd--when it is equal night all over the world.