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 aegespotomi 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 Clazomenaean 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 Clazomenaean 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


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