Precisely as the earth goes round the sun from year to year, the moon goes round the earth from month to month, and that at a distance of some 240,000 miles; the same lunar side or hemisphere being always turned toward us, although that satellite turns upon her own axis as well as the earth and the sun. The earth is in repose so far as the moon is concerned; it is her sun. The two combined, being as true a unity as any chemical molecule which is composed of two atoms, go round the sun as if they were one; the earth carries her moon with her. So that it is possible, if not probable in the first instance, that the sun, though in repose as to the earth and her moon (and, indeed, to all the planets yet to be mentioned) may be in motion on some vast orbit of his own; an orbit along which he carries all his planetary adherents with him, just as the earth takes her moon round the sun. It is curious to perceive how, not only in the case of our own moon, but in the cases of the moons of Jupiter, Saturn, and Uranus, and actually in those of all the planets considered as the moons of the sun, the Platonic epicycle really holds good. The earth turns on her heel, with the moon held out at arm's length, while she goes round the amphitheatre before the solar eye; so do the other moon-bearers. So does the sun himself upon a vaster arena and before a greater spectator, like another Briareus; holding out his seventeen planets, and nobody knows how many comets, in his hundred hands. The moons, of those solar planets which have them, represent the epi-epicyclical orbits of the Ptolemaic theory. It is curious, and also touching, to notice how often the errors of man are thus the shadows of truth. Were it not for the preceding shadows, indeed, the substance would never arrive; and therefore the Ptolemaics of the world are second, in value and in merit, only to epochal discoverers like Copernicus.