ANAXAGORAS
Sometime during the early part of this golden age
there came to Athens a middle-aged man from Clazomenæ,
who, from our present stand-point, was a
more interesting personality than perhaps any other
in the great galaxy of remarkable men assembled there.
The name of this new-comer was Anaxagoras. It was
said in after-time, we know not with what degree of
truth, that he had been a pupil of Anaximenes. If so,
he was a pupil who departed far from the teachings of
his master. What we know for certain is that Anaxagoras
was a truly original thinker, and that he became a
close friend—in a sense the teacher—of Pericles and of
Euripides. Just how long he remained at Athens is not
certain; but the time came when he had made himself
in some way objectionable to the Athenian populace
through his teachings. Filled with the spirit of the
investigator, he could not accept the current conceptions
as to the gods. He was a sceptic, an innovator.
Such men are never welcome; they are the chief factors
in the progress of thought, but they must look always
to posterity for recognition of their worth; from
their contemporaries they receive, not thanks, but
persecution. Sometimes this persecution takes one form,
sometimes another; to the credit of the Greeks be it
said, that with them it usually led to nothing more
severe than banishment. In the case of Anaxagoras,
it is alleged that the sentence pronounced was death;
but that, thanks to the influence of Pericles, this
sentence was commuted to banishment. In any event,
the aged philosopher was sent away from the city of
his adoption. He retired to Lampsacus. "It is not
I that have lost the Athenians,'' he said; "it is the
Athenians that have lost me.''
The exact position which Anaxagoras had among his
contemporaries, and his exact place in the development
of philosophy, have always been somewhat in
dispute. It is not known, of a certainty, that he even
held an open school at Athens. Ritter thinks it doubtful
that he did. It was his fate to be misunderstood,
or underestimated, by Aristotle; that in itself would
have sufficed greatly to dim his fame—might, indeed,
have led to his almost entire neglect had he not been
a truly remarkable thinker. With most of the questions
that have exercised the commentators we have
but scant concern. Following Aristotle, most historians
of philosophy have been metaphysicians; they have
concerned themselves far less with what the ancient
thinkers really knew than with what they thought.
A chance using of a verbal quibble, an esoteric phrase,
the expression of a vague mysticism—these would suffice
to call forth reams of exposition. It has been the
favorite pastime of historians to weave their own anachronistic
theories upon the scanty woof of the half-remembered thoughts of the ancient philosophers.
To make such cloth of the imagination as this is an
alluring pastime, but one that must not divert us here.
Our point of view reverses that of the philosophers.
We are chiefly concerned, not with some vague saying
of Anaxagoras, but with what he really knew regarding
the phenomena of nature; with what he observed,
and with the comprehensible deductions that he derived
from his observations. In attempting to answer
these inquiries, we are obliged, in part, to take our
evidence at second-hand; but, fortunately, some fragments
of writings of Anaxagoras have come down to
us. We are told that he wrote only a single book. It
was said even (by Diogenes) that he was the first man
that ever wrote a work in prose. The latter statement
would not bear too close an examination, yet it is true
that no extensive prose compositions of an earlier day
than this have been preserved, though numerous
others are known by their fragments. Herodotus,
"the father of prose,'' was a slightly younger contemporary
of the Clazomenæan philosopher; not unlikely
the two men may have met at Athens.
Notwithstanding the loss of the greater part of the
writings of Anaxagoras, however, a tolerably precise
account of his scientific doctrines is accessible. Diogenes
Laertius expresses some of them in very clear and
precise terms. We have already pointed out the uncertainty
that attaches to such evidence as this, but it
is as valid for Anaxagoras as for another. If we reject
such evidence, we shall often have almost nothing left;
in accepting it we may at least feel certain that we are
viewing the thinker as his contemporaries and immediate
successors viewed him. Following Diogenes,
then, we shall find some remarkable scientific opinions
ascribed to Anaxagoras. "He asserted,'' we are told,
"that the sun was a mass of burning iron, greater than
Peloponnesus, and that the moon contained houses
and also hills and ravines.'' In corroboration of this,
Plato represents him as having conjectured the right
explanation of the moon's light, and of the solar and
lunar eclipses. He had other astronomical theories
that were more fanciful; thus "he said that the stars
originally moved about in irregular confusion, so that
at first the pole-star, which is continually visible, always
appeared in the zenith, but that afterwards it acquired
a certain declination, and that the Milky Way
was a reflection of the light of the sun when the stars
did not appear. The comets he considered to be a
concourse of planets emitting rays, and the shooting-stars he thought were sparks, as it were, leaping from
the firmament.''
Much of this is far enough from the truth, as we now
know it, yet all of it shows an earnest endeavor to
explain the observed phenomena of the heavens on
rational principles. To have predicated the sun as a
great molten mass of iron was indeed a wonderful
anticipation of the results of the modern spectroscope.
Nor can it be said that this hypothesis of Anaxagoras
was a purely visionary guess. It was in all probability
a scientific deduction from the observed character of
meteoric stones. Reference has already been made
to the alleged prediction of the fall of the famous
meteor at Ægespotomi by Anaxagoras. The assertion
that he actually predicted this fall in any proper sense
of the word would be obviously absurd. Yet the fact
that his name is associated with it suggests that he had
studied similar meteorites, or else that he studied this
particular one, since it is not quite clear whether it
was before or after this fall that he made the famous
assertion that space is full of falling stones. We should
stretch the probabilities were we to assert that Anaxagoras
knew that shooting-stars and meteors were
the same, yet there is an interesting suggestiveness
in his likening the shooting-stars to sparks leaping
from the firmament, taken in connection with his observation
on meteorites. Be this as it may, the fact
that something which falls from heaven as a blazing
light turns out to be an iron-like mass may very well
have suggested to the most rational of thinkers that
the great blazing light called the sun has the same
composition. This idea grasped, it was a not unnatural
extension to conceive the other heavenly bodies
as having the same composition.
This led to a truly startling thought. Since the
heavenly bodies are of the same composition as the
earth, and since they are observed to be whirling
about the earth in space, may we not suppose that they
were once a part of the earth itself, and that they
have been thrown off by the force of a whirling motion?
Such was the conclusion which Anaxagoras
reached; such his explanation of the origin of the
heavenly bodies. It was a marvellous guess. Deduct
from it all that recent science has shown to be untrue;
bear in mind that the stars are suns, compared
with which the earth is a mere speck of dust; recall
that the sun is parent, not daughter, of the earth, and
despite all these deductions, the cosmogonic guess of
Anaxagoras remains, as it seems to us, one of the most
marvellous feats of human intelligence. It was the
first explanation of the cosmic bodies that could be
called, in any sense, an anticipation of what the
science of our own day accepts as a true explanation
of cosmic origins. Moreover, let us urge again that
this was no mere accidental flight of the imagination;
it was a scientific induction based on the only data
available; perhaps it is not too much to say that it was
the only scientific induction which these data would
fairly sustain. Of course it is not for a moment to be
inferred that Anaxagoras understood, in the modern
sense, the character of that whirling force which we
call centrifugal. About two thousand years were yet
to elapse before that force was explained as elementary
inertia; and even that explanation, let us not forget,
merely sufficed to push back the barriers of mystery
by one other stage; for even in our day inertia is a
statement of fact rather than an explanation.
But however little Anaxagoras could explain the
centrifugal force on mechanical principles, the
practical powers of that force were sufficiently open to his
observation. The mere experiment of throwing a
stone from a sling would, to an observing mind, be
full of suggestiveness. It would be obvious that by
whirling the sling about, the stone which it held would
be sustained in its circling path about the hand in
seeming defiance of the earth's pull, and after the stone
had left the sling, it could fly away from the earth to
a distance which the most casual observation would
prove to be proportionate to the speed of its flight.
Extremely rapid motion, then, might project bodies
from the earth's surface off into space; a sufficiently
rapid whirl would keep them there. Anaxagoras
conceived that this was precisely what had occurred.
His imagination even carried him a step farther—to a
conception of a slackening of speed, through which the
heavenly bodies would lose their centrifugal force,
and, responding to the perpetual pull of gravitation,
would fall back to the earth, just as the great stone at
Ægespotomi had been observed to do.
Here we would seem to have a clear conception of
the idea of universal gravitation, and Anaxagoras
stands before us as the anticipator of Newton. Were
it not for one scientific maxim, we might exalt the old
Greek above the greatest of modern natural philosophers;
but that maxim bids us pause. It is phrased
thus, "He discovers who proves.'' Anaxagoras could
not prove; his argument was at best suggestive, not
demonstrative. He did not even know the laws
which govern falling bodies; much less could he apply
such laws, even had he known them, to sidereal bodies
at whose size and distance he could only guess in the
vaguest terms. Still his cosmogonic speculation remains
as perhaps the most remarkable one of antiquity.
How widely his speculation found currency
among his immediate successors is instanced in a
passage from Plato, where Socrates is represented as
scornfully answering a calumniator in these terms:
"He asserts that I say the sun is a stone and the
moon an earth. Do you think of accusing Anaxagoras,
Miletas, and have you so low an opinion of these
men, and think them so unskilled in laws, as not to
know that the books of Anaxagoras the Clazomenæan
are full of these doctrines. And forsooth the young
men are learning these matters from me which sometimes
they can buy from the orchestra for a drachma,
at the most, and laugh at Socrates if he pretends they
are his-particularly seeing they are so strange.''
The element of error contained in these cosmogonic
speculations of Anaxagoras has led critics to do them
something less than justice. But there is one other
astronomical speculation for which the Clazomenæan
philosopher has received full credit. It is generally
admitted that it was he who first found out the explanation
of the phases of the moon; a knowledge that
that body shines only by reflected light, and that its
visible forms, waxing and waning month by month
from crescent to disk and from disk to crescent, merely
represent our shifting view of its sun-illumined face.
It is difficult to put ourselves in the place of the ancient
observer and realize how little the appearances
suggest the actual fact. That a body of the same
structure as the earth should shine with the radiance
of the moon merely because sunlight is reflected from
it, is in itself a supposition seemingly contradicted by
ordinary experience. It required the mind of a philosopher,
sustained, perhaps, by some experimental observations,
to conceive the idea that what seems so
obviously bright may be in reality dark. The germ
of the conception of what the philosopher speaks of
as the noumena, or actualities, back of phenomena
or appearances, had perhaps this crude beginning.
Anaxagoras could surely point to the moon in support
of his seeming paradox that snow, being really composed
of water, which is dark, is in reality black and
not white—a contention to which we shall refer more
at length in a moment.
But there is yet another striking thought connected
with this new explanation of the phases of the moon.
The explanation implies not merely the reflection of
light by a dark body, but by a dark body of a particular
form. Granted that reflections are in question,
no body but a spherical one could give an appearance
which the moon presents. The moon, then, is
not merely a mass of earth, it is a spherical mass
of earth. Here there were no flaws in the reasoning
of Anaxagoras. By scientific induction he passed
from observation to explanation. A new and most
important element was added to the science of astronomy.
Looking back from the latter-day stand-point, it
would seem as if the mind of the philosopher must
have taken one other step: the mind that had conceived
sun, moon, stars, and earth to be of one substance
might naturally, we should think, have reached
out to the further induction that, since the moon is a
sphere, the other cosmic bodies, including the earth,
must be spheres also. But generalizer as he was, Anaxagoras
was too rigidly scientific a thinker to make
this assumption. The data at his command did not,
as he analyzed them, seem to point to this conclusion.
We have seen that Pythagoras probably, and Parmenides
surely, out there in Italy had conceived the
idea of the earth's rotundity, but the Pythagorean
doctrines were not rapidly taken up in the mother-country, and Parmenides, it must be recalled, was a
strict contemporary of Anaxagoras himself. It is no
reproach, therefore, to the Clazomenæan philosopher
that he should have held to the old idea that the
earth is flat, or at most a convex disk—the latter being
the Babylonian conception which probably dominated
that Milesian school to which Anaxagoras harked
back.
Anaxagoras may never have seen an eclipse of the
moon, and even if he had he might have reflected that,
from certain directions, a disk may throw precisely the
same shadow as a sphere. Moreover, in reference to
the shadow cast by the earth, there was, so Anaxagoras
believed, an observation open to him nightly which,
we may well suppose, was not without influence in
suggesting to his mind the probable shape of the earth.
The Milky Way, which doubtless had puzzled astronomers
from the beginnings of history and which was
to continue to puzzle them for many centuries after
the day of Anaxagoras, was explained by the Clazomenæan
philosopher on a theory obviously suggested
by the theory of the moon's phases. Since the earth-like moon shines by reflected light at night, and
since the stars seem obviously brighter on dark nights,
Anaxagoras was but following up a perfectly logical
induction when he propounded the theory that the
stars in the Milky Way seem more numerous and
brighter than those of any other part of the heavens,
merely because the Milky Way marks the shadow of
the earth. Of course the inference was wrong, so far
as the shadow of the earth is concerned; yet it contained
a part truth, the force of which was never fully recognized
until the time of Galileo. This consists in the
assertion that the brightness of the Milky Way is
merely due to the glow of many stars. The shadow-theory of Anaxagoras would naturally cease to have
validity so soon as the sphericity of the earth was
proved, and with it, seemingly, fell for the time the
companion theory that the Milky Way is made up of
a multitude of stars.
It has been said by a modern critic [62]
that the shadow-theory was childish in that it failed to note
that the Milky Way does not follow the course of the
ecliptic. But this criticism only holds good so long
as we reflect on the true character of the earth as a
symmetrical body poised in space. It is quite possible
to conceive a body occupying the position of the
earth with reference to the sun which would cast a
shadow having such a tenuous form as the Milky Way
presents. Such a body obviously would not be a
globe, but a long-drawn-out, attenuated figure. There
is, to be sure, no direct evidence preserved to show that
Anaxagoras conceived the world to present such a
figure as this, but what we know of that philosopher's
close-reasoning, logical mind gives some warrant to
the assumption—gratuitous though in a sense it be—
that the author of the theory of the moon's phases had
not failed to ask himself what must be the form of that
terrestrial body which could cast the tenuous shadow
of the Milky Way. Moreover, we must recall that the
habitable earth, as known to the Greeks of that day,
was a relatively narrow band of territory, stretching
far to the east and to the west.