Aristotle
proskei=tai. panto\s de\ peperasme/nou sô/matos pro\s peperasme/non
ê( du/nami/s e)stin.]).[1]
[Footnote 1: [See Prantl's note on this difficult passage in his
German translation of the De Coelo, p. 309 (Leipzig, 1857).]]
CH. 13.--Having thus explained, respecting the Stars and Planets
which are carried round in circular motion, what is their essence,
figure, current, and order of position, we now proceed to speak of
the Earth: What is its position? Whether is it at rest or in motion?
What is its figure?
Philosophers differ respecting the position of the Earth. Most of
those who conceive the entire Kosmos as finite, declare the Earth to
be in its centre. But the Italian philosophers, called Pythagoreans,
are of an opposite opinion; affirming that Fire is in the centre, and
that the Earth, being one of the stars revolving round the centre,
makes night and day. They assume moreover another Earth opposite to
this ([Greek: e)nanti/an a)/llên tau/tê|])--which other they call
_Antichthon_. Herein they do not adjust their theories and look out
for causes adapted to the phenomena; but, on the contrary, they
distort the phenomena so as to suit their own doctrines and
reasonings, and try to constitute themselves auxiliary governors of
the Kosmos ([Greek: peirô/menoi sugkosmei=n]--s. 1). And, if we are
to look for assurance not to the phenomena but to our own reasonings,
many others might agree with them, that it is not proper ([Greek:
mê\ dei=n]) to assign to the Earth the central place. They think
that the most honourable place belongs to the most honourable body,
and that Fire is more honourable than Earth; that the two extremes,
centre and circumference, are more honourable than the parts
intermediate between them. Upon these grounds they consider that Fire
and not Earth is at the centre of the Universal Sphere; and they have
another reason, peculiar to themselves, for this conclusion: they
hold that the centre is the most important place in the universe, and
that it ought as such to be the most carefully guarded; wherefore
they call it the watch of Zeus ([Greek: Dio\s phulakê/n]), and
regard it as occupied by Fire (s. 2).
This assumes that what is absolutely (_i.e._, without subjoining any
qualifying adjunct), described as _the centre_, is at once centre of
the magnitude, centre of the object, and centre of nature. But we
ought rather to follow the analogy of animals, where the same point
is not the centre of the animal and the centre of the body: the case
is the same in the entire Kosmos. Hence the Pythagoreans need not
feel any anxiety about the Universe ([Greek: ou)the\n au)tou\s dei=
thorubei=sthai peri\ to\ pa=n]), nor introduce a guard at the centre.
They ought rather to enquire where and of what character the middle
point is; for that middle point is the true beginning and the
honourable. The middle of the place occupied is rather like an end
than like a beginning; for that which is limited is the middle, that
which limits is the boundary: now that which comprehends and is
boundary, is more honourable than that which is bounded; the former
is the Essence of the entire compound, the latter is only its Matter
(s. 3).
As about the place of the Earth, so also about its motion or rest,
philosophers differ. The Pythagoreans and those who do not even place
it at the centre, consider it to revolve in a circle, and they
consider the Antichthon to revolve in like manner. Some even think it
possible that there may be many other bodies carried round the centre
in like manner, though invisible to us, by reason of the obstructing
body of the Earth. Hence (they say) the eclipses of the moon are more
frequent than those of the Sun; since not only the Earth, but also
each of these unseen bodies, causes the Moon to be eclipsed. For, the
Earth not being a point, we on the circumference thereof, even
assuming it to occupy the centre, are distant from the centre by the
entire hemisphere of the Earth; yet we do not find out that we are
not in the centre, and astronomical appearances present themselves to
us just as if we were so. Thus it happens (according to these
philosophers), the Earth not being in the centre at all: the
appearances presented to us are just the same as if we were at the
centre.
Again, there are some who (like Plato in Timæus) affirm that the
Earth, though situated in the centre, is packed and revolves round
the axis stretched across the universe (s. 4).
About the figure of the Earth, there is no less difference of
opinion. Some say that it is spherical; others, that it is flat and
in shape like a tambourine ([Greek: tumpanoeidê/s]). These last
adduce as proof, that the Sun, at rising and setting, exhibits a
rectilinear section or eclipse of his disk and not a circular one,
when partially concealed by the Earth, and becoming invisible under
the horizon or visible above the horizon. They do not take proper
account of the vast distance of the Sun and the magnitude of his
circumference. The segment of a long circle appears from a distance
like a straight line. These philosophers further add, that the flat
tambourine-like shape must be inferred of necessity from the fact
that the Earth remains stationary (s. 5).
Upon this disputed question, a feeling of perplexity comes
unavoidably upon every one. It would argue a very irrational mind not
to wonder how a small piece of the Earth, if suspended in the air, is
carried downward and will not stop of itself, and the larger piece is
carried downward more quickly than the smaller; while nevertheless
the entire Earth, if suspended in like manner, would not be so
carried. In spite of its great weight, it remains stationary (s. 6).
But the solutions of this problem which some suggest are more strange
and full of perplexity, and it is surprising that they have not been
so considered. The Kolophonian Xenophanes affirmed that the lower
depths of the Earth were rooted downwards to infinity, in order to
escape the troublesome obligation of looking for a reason why it
remained stationary. Others say, that the Earth rests upon water,
floating thereupon like wood: this is an ancient doctrine promulgated
by Thales; as if there were not as much perplexity about the water
which supports the Earth, as there is about the Earth itself. For it
is not the nature of water to remain suspended, but always to rest
upon something (s. 7). Moreover, air is lighter than water, and water
lighter than earth; how then can these men think that the substance
naturally lighter can lie below the substance naturally heavier?
Besides, if it were the nature of the whole Earth to remain resting
on water, it must be the nature of each part of the Earth to do the
same; but this does not happen: each part of the earth is carried
down to the bottom, and the greater part more quickly than the less
(s. 8).
All these philosophers carry their researches to a certain point, but
not to the bottom of the problem. It is indeed a habit with all of us
to conduct our enquiries not with reference to the problem itself,
but with reference to our special opponents. If we have no opponent
but are conducting our investigations alone, we pursue them as far as
that point where we can make no farther objections to ourselves.
Whoever therefore intends to investigate completely must take care to
make objections to himself upon all the points of objection which
really belong to the subject; and this he can only do after having
thoroughly surveyed all the differences of opinion and doctrine (s.
9).
The reason why the Earth remains at rest, Anaximenes, Anaxagoras, and
Demokritus, declare to be its breadth or flatness ([Greek: to\
pla/tos]): it does not (they say) divide the air beneath, but covers
over the air like a lid ([Greek: ou) ga\r te/mnein, a)ll'
e)pipômati/zein to\n a)e/ra to\n ka/tôthen]); as we see that flat
and spreading bodies usually do, being difficult to be moved and
making strong resistance even against the winds. The Earth does the
same, through its flatness, against the air beneath, which remains at
rest there (in the opinion of these philosophers) because it finds no
sufficient place into which to travel, like water in a _klepsydra_:
they also produce many evidences to show that air thus imprisoned,
while remaining stationary, can support a heavy weight (s. 10).
Now, in the first place, these men affirm that, unless the shape of
the Earth were flat, it would not remain at rest. Yet on their own
showing it is not alone the flat shape of the earth which causes it
to remain at rest, but rather its magnitude. For the air beneath
remains _in situ_ by reason of its vast mass, finding no means of
escape through the narrow passage: and the mass of the air is thus
vast, because it is imprisoned inside by the great magnitude of the
Earth; which effect will be produced in the same manner, even though
the Earth be spherical, provided it be of its present magnitude.
Moreover, philosophers who hold this opinion about the motion of the
Earth, think only of its motion as a whole, and take no account of
its parts. For they ought to define at the first step whether bodies
have or have not one special mode of motion by nature; and, if none
by nature, then whether they have any mode of motion violent or
contra-natural. I have already determined this point as well as my
powers admitted, and shall therefore assume the results as settled.
If there be no special motion natural to bodies, neither will there
be any which is contra-natural or violent; and, if there be none
either natural or violent, no body will be moved at all. I have
already shown that this is a necessary consequence; and, farther,
that (upon that supposition) there can be no body even at rest; for
rest, like motion, is either natural or contra-natural; and, if there
be any special mode of motion which is natural, neither
contra-natural motion, nor contra-natural rest, can stand alone
(ss. 11-13).
Let us then assume (reasoning on the hypothesis of these
philosophers) that the Earth now remains in its present place
contrary to nature, and that it was carried into aggregation at the
centre by the revolution of the Kosmos (also contrary to
nature--[Greek: kai\ sunê=lthen e)pi\ to\ me/son pherome/nê dia\ tê\n
di/nêsin]--s. 14). For all those who recognize a generation of the
Kosmos assign this revolution as the cause which determined the
aggregation of the Earth at the centre, upon the analogy of particles
carried round in liquids or in air, where the larger and heavier
particles are always carried to the centre of the revolution. They
profess thus to know the cause which determined the Earth to _come
to_ the centre; but what they seek to find out is the cause which
determines it to remain there, and upon that they differ: some
saying, as has been stated just now, that its breadth and magnitude
is the cause; others, with Empedokles, ascribing the fact to the
revolution of the Heaven, the extreme velocity of which checks the
fall of the Earth downward, just as water in a cup may be whirled
rapidly round without falling to the ground. But suppose absence of
these two causes: in which direction will the Earth be naturally
carried? Not to the centre; for (upon the doctrine which we are now
criticising) its motion to the centre, and its remaining at the
centre, are both of them contra-natural; but some special mode of
motion, natural to the Earth, there must necessarily be. Is this
upward, or downward, or in what other direction? If there be no
greater tendency downward than upward, and if the air above does not
hinder the Earth from tending upward, neither will the air beneath
hinder it from tending downwards: the same causes produce the same
effects, operating on the same matter (ss. 14, 15).