An introduction to mathematics, by A. N. Whitehead.

PERIODICITY IN NATURE 165
ancient times, in climates where the days are
burning and the skies clear, human life was
apparently largely influenced by the existence
of moonlight. Accordingly our divisions into
weeks and months, with their religious associations, have spread over the European races
from Syria and Mesopotamia, though independent observances following the moon's
phases are found amongst most nations. It
is, however, throughthetides, and not through
its phases of light and darkness, that the
moon's periodicity has chiefly influenced the
history of the earth.
Our bodily life is essentially periodic.
It is dominated by the beatings of the
heart, and the recurrence of breathing.
The presupposition of periodicity is indeed
fundamental to our very conception of life.
We cannot imagine a course of nature in
which, as events progressed, we should be
unable to say: "This has happened before."
The whole conception of experience as a guide
to conduct would be absent. Men would
always find themselves in new situations
possessing no substratum of identity with
anything in past history. The very means of
measuring time as a quantity would be absent. Events might still be recognized as
occurring in a series, so that some were earlier
and others later. But we now go beyond this
bare recognition. We can not only say that