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 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.