So long as sun, moon, and planets were supposed to be gods or angels; so long as the sword of Orion was not a metaphor, but a fact, and the groups of stars which inlaid the floor of heaven were the glittering trophies of the loves and wars of the Pantheon, so long there was no science of Astronomy. There was fancy, imagination, poetry, perhaps reverence, but no science. As soon, however, as it was observed that the stars retained their relative places--that the times of their rising and setting varied with the seasons--that sun, moon, and planets moved among them in a plane, and the belt of the Zodiac was marked out and divided, then a new order of things began. Traces of the earlier stage remained in the names of the signs and constellations, just as the Scandinavian mythology survives now in the names of the days of the week: but for all that, the understanding was now at work on the thing; Science had begun, and the first triumph of it was the power of foretelling the future. Eclipses were perceived to recur in cycles of nineteen years, and philosophers were able to say when an eclipse was to be looked for. The periods of the planets were determined. Theories were invented to account for their eccentricities; and, false as those theories might be, the position of the planets could be calculated with moderate certainty by them. The very first result of the science, in its most imperfect stage, was a power of foresight; and this was possible before any one true astronomical law had been discovered. We should not therefore question the possibility of a science of history, because the explanations of its phenomena were rudimentary or imperfect: that they might be, and might long continue to be, and yet enough might be done to show that there was such a thing, and that it was not entirely without use. But how was it that in those rude days, with small knowledge of mathematics, and with no better instruments than flat walls and dial plates, those first astronomers made progress so considerable? Because, I suppose, the phenomena which they were observing recurred, for the most part, within moderate intervals; so that they could collect large experience within the compass of their natural lives: because days and months and years were measurable periods, and within them the more simple phenomena perpetually repeated themselves. But how would it have been if, instead of turning on its axis once in twenty-four hours, the earth had taken a year about it; if the year had been nearly four hundred years; if man's life had been no longer than it is, and for the initial steps of astronomy there had been nothing to depend upon except observations recorded in history? How many ages would have passed, had this been our condition, before it would have occurred to any one, that, in what they saw night after night, there was any kind of order at all?