ARISTOTLE (384-322 B.C.)
When we pass to that third great Athenian teacher,
Aristotle, the case is far different. Here was a man
whose name was to be received as almost a synonym
for Greek science for more than a thousand years
after his death. All through the Middle Ages his writings
were to be accepted as virtually the last word regarding
the problems of nature. We shall see that his
followers actually preferred his mandate to the testimony
of their own senses. We shall see, further, that
modern science progressed somewhat in proportion
as it overthrew the Aristotelian dogmas. But the
traditions of seventeen or eighteen centuries are not
easily set aside, and it is perhaps not too much to say
that the name of Aristotle stands, even in our own
time, as vaguely representative in the popular mind
of all that was highest and best in the science of antiquity.
Yet, perhaps, it would not be going too far
to assert that something like a reversal of this judgment
would be nearer the truth. Aristotle did, indeed,
bring together a great mass of facts regarding
animals in his work on natural history, which, being
preserved, has been deemed to entitle its author to be
called the "father of zoology.'' But there is no reason
to suppose that any considerable portion of this work
contained matter that was novel, or recorded observations
that were original with Aristotle; and the classifications
there outlined are at best but a vague foreshadowing
of the elaboration of the science. Such as
it is, however, the natural history stands to the credit
of the Stagirite. He must be credited, too, with a
clear enunciation of one most important scientific
doctrine—namely, the doctrine of the spherical figure
of the earth. We have already seen that this theory
originated with the Pythagorean philosophers out in
Italy. We have seen, too, that the doctrine had not
made its way in Attica in the time of Anaxagoras.
But in the intervening century it had gained wide currency,
else so essentially conservative a thinker as
Aristotle would scarcely have accepted it. He did
accept it, however, and gave the doctrine clearest and
most precise expression. Here are his words:
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"As to the figure of the earth it must necessarily be
spherical.... If it were not so, the eclipses of the moon
would not have such sections as they have. For in the
configurations in the course of a month the deficient
part takes all different shapes; it is straight, and concave,
and convex; but in eclipses it always has the line
of divisions convex; wherefore, since the moon is
eclipsed in consequence of the interposition of the earth,
the periphery of the earth must be the cause of this by
having a spherical form. And again, from the appearance
of the stars it is clear, not only that the earth is
round, but that its size is not very large; for when we
make a small removal to the south or the north, the
circle of the horizon becomes palpably different, so
that the stars overhead undergo a great change, and
are not the same to those that travel in the north and
to the south. For some stars are seen in Egypt or at
Cyprus, but are not seen in the countries to the north
of these; and the stars that in the north are visible
while they make a complete circuit, there undergo a
setting. So that from this it is manifest, not only that
the form of the earth is round, but also that it is a part
of a not very large sphere; for otherwise the difference
would not be so obvious to persons making so small a
change of place. Wherefore we may judge that those
persons who connect the region in the neighborhood
of the pillars of Hercules with that towards India, and
who assert that in this way the sea is one, do not assert
things very improbable. They confirm this conjecture
moreover by the elephants, which are said to
be of the 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,
remained in vogue until superseded by that of Cuvier in
the nineteenth century. It is not to be supposed that
all the terms of Aristotle's classification originated
with him. Some of the divisions are too patent to
have escaped the observation of his predecessors.
Thus, for example, the distinction between birds and
fishes as separate classes of animals is so obvious that
it must appeal to a child or to a savage. But the
efforts of Aristotle extended, as we shall see, to less
patent generalizations. At the very outset, his grand
division of the animal kingdom into blood-bearing and
bloodless animals implies a very broad and philosophical
conception of the entire animal kingdom.
The modern physiologist does not accept the classification,
inasmuch as it is now known that colorless fluids
perform the functions of blood for all the lower organisms.
But the fact remains that Aristotle's grand
divisions correspond to the grand divisions of the
Lamarckian system—vertebrates and invertebrates—
which every one now accepts. Aristotle, as we have
said, based his classification upon observation of the
blood; Lamarck was guided by a study of the skeleton.
The fact that such diverse points of view could direct
the observer towards the same result gives,
inferentially, a suggestive lesson in what the modern
physiologist calls the homologies of parts of the
organism.
Aristotle divides his so-called blood-bearing animals
into five classes: (1) Four-footed animals that bring
forth their young alive; (2) birds; (3) egg-laying four-footed animals (including what modern naturalists
call reptiles and amphibians); (4) whales and their
allies; (5) fishes. This classification, as will be observed,
is not so very far afield from the modern divisions
into mammals, birds, reptiles, amphibians, and
fishes. That Aristotle should have recognized the
fundamental distinction between fishes and the fish-like whales, dolphins, and porpoises proves the far
from superficial character of his studies. Aristotle
knew that these animals breathe by means of lungs and
that they produce living young. He recognized, therefore,
their affinity with his first class of animals, even
if he did not, like the modern naturalist, consider these
affinities close enough to justify bringing the two types
together into a single class.
The bloodless animals were also divided by Aristotle
into five classes—namely: (1) Cephalopoda (the
octopus, cuttle-fish, etc.); (2) weak-shelled animals
(crabs, etc.); (3) insects and their allies (including
various forms, such as spiders and centipedes, which
the modern classifier prefers to place by themselves);
(4) hard-shelled animals (clams, oysters, snails, etc.);
(5) a conglomerate group of marine forms, including
star-fish, sea-urchins, and various anomalous forms
that were regarded as linking the animal to the vegetable
worlds. This classification of the lower forms of
animal life continued in vogue until Cuvier substituted
for it his famous grouping into articulates, mollusks,
and radiates; which grouping in turn was in part superseded
later in the nineteenth century.
What Aristotle did for the animal kingdom his pupil,
Theophrastus, did in some measure for the vegetable
kingdom. Theophrastus, however, was much less a
classifier than his master, and his work on botany,
called The Natural History of Development, pays comparatively
slight attention to theoretical questions.
It deals largely with such practicalities as the making
of charcoal, of pitch, and of resin, and the effects of
various plants on the animal organism when taken as
foods or as medicines. In this regard the work of
Theophrastus, is more nearly akin to the natural history
of the famous Roman compiler, Pliny. It remained,
however, throughout antiquity as the most
important work on its subject, and it entitles Theophrastus
to be called the "father of botany.'' Theophrastus
deals also with the mineral kingdom after
much the same fashion, and here again his work is the
most notable that was produced in antiquity.