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

166 INTRODUCTION TO MATHEMATICS
three events, A, B, C, occurred in this order,
so that A came before B, and B before C;
but also we can say that the length of time
between the occurrences of A and B was
twice as long as that between B and C. Now,
quantity of time is essentially dependent on
observing the number of natural recurrences
which have intervened. We may say that
the length of time between A and B was
so many days, or so many months, or so
many years, according to the type of recurrence to which we wish to appeal. Indeed,
at the beginning of civilization, these three
modes of measuring time were really distinct.
It has been one of the first tasks of science
among civilized or semi-civilized nations, to
fuse them into one coherent measure. The
full extent of this task must be grasped. It
is necessary to determine, not merely what
number of days (e.g. 365 25...) go to some
one year, but also previously to determine
that the same number of days do go to the
successive years. We can imagine a world in
which periodicities exist, but such that no two
are coherent. In some years there might be
200 days and in others 350. The determination of the broad general consistency of the
more important periodicities was the first step
in natural science. This consistency arises
from no abstract intuitive law of thought;
it is merely an observed fact of nature