movements of the planets and their satellites. What results from
conceptions of this order? Amazing things! If our space is curved in
higher space, you may be looking toward the back of your own head.
If time flows in cycles, in travelling toward to-morrow you may be
facing yesterday.

This "eternal return," so far from being a new idea, is so old that
it has been forgotten. Its reappearance in novel guise, along with
so many other recrudescences, itself beautifully illustrates time
curvature in consciousness. _Yugas_, time cycles, are an integral
and inexpugnable part of Oriental metaphysics. "Since the soul
perpetually runs," says Zoroaster, "in a certain space of time it
passes through all things, which circulation being accomplished, it
is compelled to run back again through all things, and unfold the
same web of generation in the world." Time curvature is implicit in
the Greek idea of the iron, bronze, silver, and golden ages,
succeeding each other in the same order: the winter, seed-time,
summer and harvest of the larger year. Astrology, seership, prophecy,
become plausible on the higher-time hypothesis. From this point of
view history becomes less puzzling and paradoxical. What were the
Middle Ages but a forgetting of Greek and Roman civilization, and
what was the Renaissance but a remembering of them--a striving to
re-create the ruined stage-settings and to re-enact the urbane play
of Pagan life. The spirit of the Crusades is now again animate
throughout Europe. Nations are uniting in a Holy War against the
Infidel _de nos jours_.

But it is in the individual consciousness that time curvature
receives its most striking confirmation--those lesser returns and
rhythms to which we give the name of periodicity. Before considering