e same species towards each extreme; as if
this circumstance was a consequence of the conjunction of the
extremes. The mathematicians who try to calculate the measure of the
circumference, make it amount to four hundred thousand stadia; whence we
collect that the earth is not only spherical, but is not large compared
with the magnitude of the other stars."

But in giving full meed of praise to Aristotle for the promulgation of
this doctrine of the sphericity of the earth, it must unfortunately be
added that the conservative philosopher paused without taking one other
important step. He could not accept, but, on the contrary, he expressly
repudiated, the doctrine of the earth's motion. We have seen that this
idea also was a part of the Pythagorean doctrine, and we shall have
occasion to dwell more at length on this point in a succeeding chapter.
It has even been contended by some critics that it was the adverse
conviction of the Peripatetic philosopher which, more than any other
single influence, tended to retard the progress of the true doctrine
regarding the mechanism of the heavens. Aristotle accepted the
sphericity of the earth, and that doctrine became a commonplace of
scientific knowledge, and so continued throughout classical antiquity.
But Aristotle rejected the doctrine of the earth's motion, and that
doctrine, though promulgated actively by a few contemporaries and
immediate successors of the Stagirite, was then doomed to sink out of
view for more than a thousand years. If it be a correct assumption that
the influence of Aristotle was, in a large measure, responsible for this
result, then we shall perhaps not be far astray in assuming that
the great founder of the Peripatetic school was, on the whole, more
instrumental in retarding the progress of astronomical science that any
other one man that ever lived.

The field of science in which Aristotle was pre-eminently a pathfinder
is zoology. His writings on natural history have largely been preserved,
and they constitute by far the most important contribution to the
subject that has come down to us from antiquity. They show us that
Aristotle had gained possession of the widest range of facts regarding
the animal kingdom, and, what is far more important, had attempted to
classify these facts. In so doing he became the founder of systematic
zoology. Aristotle's classification of the animal kingdom was known
and studied throughout the Middle Ages, and, in fact, rem