Aristotle
A farther argument becomes applicable, when we are reasoning against
Empedokles. When the four elements were first separated out of their
confused huddle by the influence of Contention, what was the cause
for the Earth to remain still and _in situ_? Empedokles cannot claim
to introduce then the agency of the cosmical revolution. Moreover, it
is strange that he should not have reflected that in the first
instance the particles and fragments of the Earth were carried to the
centre. But what is the cause now that every thing having weight is
carried towards the Earth? It cannot be the revolution of the Heaven
which brings these things nearer to us (s. 16).
Again, Fire is carried upward. What is the cause of this? The
revolution of the Heaven cannot cause it. But, if it be the nature of
fire to be carried in one certain direction, it must be equally the
nature of Earth to be carried in one certain direction. Light and
heavy, also, are not discriminated by the heavenly revolution. There
are matters originally heavy, and matters originally light: the
former are carried to the centre, the latter to the circumference,
each by its own special motion. Even prior to the heavenly revolution
there existed things intrinsically light and intrinsically heavy;
which are discriminated by certain attributes--a certain natural mode
of motion and a certain place. In infinite space, there can be no
upward and downward; and it is by this (local distinction) that light
and heavy are discriminated (ss. 17, 18).
While most philosophers insist upon the causes just noticed why the
Earth remains stationary where it is, there are others, like
Anaximander, among the ancients, who say that it remains so because
of its likeness or equality ([Greek: dia\ tê\n o(moio/tera]--equal
tendency in all directions). That which is situated in the centre
(they say) and which has like relation to the extreme parts (_i.e._,
like to _all_ the extreme parts) ought not to be carried any more
upward or downward or sideways; and it cannot be moved in opposite
directions at once; so that it remains stationary by necessity (s.
19).
This doctrine is ingenious, but not true. For the property affirmed
is noway peculiar to the Earth: the affirmation is, that every thing
which is placed at the centre must of necessity remain there; so that
Fire also would remain there at rest, as well as Earth. But this
necessity must be denied. For it is shown by observation that the
Earth not only remains at the centre, but is carried to the centre;
since each part of it is carried thither, and, whithersoever the
parts are carried, the whole is carried necessarily to the same
point. The peculiar property of the earth therefore is, not (as this
hypothesis declares) to have like relation to all the extreme
parts--for that is common to all the elements--but to be carried
towards the centre (ss. 20, 21).
Moreover, it is absurd to investigate why the Earth remains at the
centre, and not to investigate equally why Fire remains at the
extremity. For, if you explain this last by saying that Fire has its
natural place at the extremity, the Earth must have its natural place
somewhere else. If the centre be not the natural place of the Earth,
and if the Earth remains there through like tendency in all
directions, like the hair in equal tension or the man both hungry and
thirsty between food and drink, you must equally assign the reason
why Fire remains at the extremity. It is singular too that you should
try to explain only the _remaining at rest_ ([Greek: monê=s]) of the
Earth, and not also seek to explain the natural current ([Greek:
phora/])--why Earth is carried downward, and Fire upward, when there
is no opposing force (s. 22).
Nor can it be admitted that the doctrine is true. Thus much indeed is
true by accident--that every thing which has no greater obligation to
be moved in this direction than in that, must necessarily remain at
the centre. But this is true only so long as it remains a compact
whole; for, according to the theory which we are discussing, it will
not remain stationary, but will be moved: not indeed as a whole, but
dispersed into parts (s. 23: [Greek: a)lla\ mê\n ou)de\ a)lêthe/s
e)sti to\ lego/menon. kata\ sumbebêko\s me/ntoi tou=to/ ge
a)lêthe/s, ô(s a)nagkai=on me/nein e)pi\ tou= me/sou pa=n, ô(=|
mêthe\n ma=llon deu=ro ê( deu=ro kinei=sthai prosê/kei. a)lla\
dia/ ge tou=ton to\n lo/gon ou) menei= a)lla\ kinêthê/setai; ou)
me/ntoi o(/lon, a)lla\ diespasme/non.]--I understand [Greek: kata\
sumbebêko/s] to mean, subject to the condition of its remaining a
compact whole). For the same reasoning would apply to Fire as well as
to Earth: it would prove that Fire, if placed at the centre, will
remain there just as much as Earth, because Fire will have like
relation to each point of the extreme periphery. Yet nevertheless it
will (not remain at the centre, but will) be carried away, if not
impeded, as we observe that it is carried in fact, to the periphery;
only not all to one and the same point of the periphery, but
corresponding portions of the Fire to corresponding portions of the
periphery: I mean, that the fourth part (_e.g._) of the Fire will be
carried to the fourth part of the periphery; for a point is no real
part of bodies ([Greek: ou)the\n ga\r stigmê\ tô=n sôma/tôn
e)sti/n]). This is the only necessary consequence flowing from the
principle of likeness of relation. As, if supposed to be put all
together at the centre, it would contract from a larger area into a
smaller, so, when carried away from the centre to the different parts
of the periphery, it would become rarer and would expand from a
smaller area into a larger. In like manner the Earth also would be
moved away from the centre, if you reason upon this principle of
likeness of relation, and if the centre were not the place belonging
to it by nature (s. 24).
CH. 14.--Having thus reported the suppositions of others respecting
the figure, place, rest and motion, of the Earth, I shall now deliver
my own opinion, first, whether it is in motion or at rest; for some
philosophers, as I have said, regard it as one of the stars (and
therefore not in the centre, but moving round the centre--the
Pythagorean theory); others (as Plato), though they place it in the
centre, consider it to be packed and moved round the middle of the
axis of the Kosmos ([Greek: oi( de\ e)pi\ tou= me/sou the/ntes,
ei)lei=sthai kai\ kinei=sthai/ phasi peri\ to\n me/son po/lon]).
That neither of these hypotheses is possible, we shall perceive if we
take as our point of departure--That, if the Earth be carried round,
whether in the centre or apart from the centre, such motion must
necessarily be violent or contra-natural. Such motion does not belong
naturally to the Earth itself; for, if such were the fact, it would
belong equally to each portion of the Earth, whereas we see that all
these portions are carried in a straight line to the centre. Being
thus violent or contra-natural, it cannot possibly be eternal. But
the order of the Kosmos is eternal. Besides, all the bodies which are
carried round in a circular revolution (all except the First or
Outermost Sphere--the Aplanês) appear to observation as lagging
behind and as being moved in more than one current. The like ought to
happen with the Earth, if moved round, whether on the centre or apart
from the centre: it ought to be moved in two currents; and, as a
consequence thereof, there ought to be side-motions and back-turnings
of the stars fastened in their sphere. But we see by observation that
this does not happen; and that the same stars always rise and set at
the same places of the Earth (s. 1).
Farthermore, the natural current both of the entire Earth and of each
of its parts is towards the middle of the universe: this is the
reason why it is at the centre, even though it happens to be actually
there at present ([Greek: dia\ tou=to ga\r, ka)\n ei) tugcha/nei
keime/nê nu=n e)pi\ tou= ke/ntrou]--he means that though actually
there, it remains there not through any force of inertia or other
cause, but because it has a natural current towards the centre). You
might start a doubt, indeed, since the centre of the Universe
coincides with the centre of the Earth, to which of the two it is
that the current of heavy bodies naturally tends: whether they tend
thereto because it is the centre of the Universe, or because it is
the centre of the Earth. We must however necessarily suppose the
former; since Fire and light bodies, whose current is the contrary of
the current of heavy bodies, are carried to the extreme periphery of
the Universe, or of that place which comprehends and surrounds the
centre of the Universe (ss. 2, 3). But it happens ([Greek:
sumbe/bêke]: it is an accompanying fact) that the same point is
centre of the Universe and centre of the Earth; accordingly heavy
bodies are carried by accident ([Greek: kata\ sumbebêko/s]--by
virtue of this accompanying fact) to the centre of the Earth; and the
proof that they are carried to this same point is, that their lines
of direction are not parallel but according to similar angles (s. 4).
That the Earth therefore is at the centre, and that it is at rest, we
may see by the foregoing reasons, as well as by the fact, that stones
thrown upwards to ever so great a height, are carried back in the
same line of direction to the same point (s. 5).
We may see farther the cause why the Earth remains at rest. For, if
its natural current be from all directions towards the centre, as
observation shows, and that of Fire from the centre to the
periphery,--no portion of it can possibly be carried away from the
centre, except by violence. For to one body belongs one current of
motion, and to a simple body a simple current--not the two opposite
currents; and the current _from_ the centre is opposite to the
current _to_ the centre. If, therefore, it be impossible for any
portion of the Earth to be carried in a direction away from the
centre, it is yet more impossible for the whole Earth to be so; for
the natural current of each part is the same as that of the whole.
Accordingly, since the Earth cannot be moved except by a superior
force or violence, it must necessarily remain stationary at the
centre (s. 6). The same conclusion is confirmed by what we learn from
geometers respecting astronomy; for all the phenomena of the
Heavens--the changes in figure, order, and arrangement of the
stars--take place as if the Earth were in the centre (s. 7).
The figure of the Earth is necessarily spherical. For each of its
parts has gravity, until it reaches the centre; and the lesser part,
pushed forward by the greater, cannot escape laterally, but must
become more and more squeezed together, one part giving place to the
other, until the centre itself is reached. We must conceive what is
here affirmed as occurring in a manner like what some of the ancient
physical philosophers tell us, except that _they_ ascribe the
downward current to an extraneous force; whereas we think it better
to state the truth, and to say that it occurs because _by nature_ all
heavy bodies are carried towards the centre. Since, therefore, the
preliminary Chaos or hotchpotch existed in power (or with its
inherent powers existing though not exercised), the elements (those
which had gravity), were carried from all sides equally towards the
centre ([Greek: e)n duna/mei ou)=n o)/ntos tou= mi/gmatos, ta\
diakrino/mena e)phe/reto o(moi/ôs pa/ntothen pro\s to\ me/son]--this
is an allusion to the doctrine of Anaxagoras); indeed, whether
brought together at the centre equally from all the periphery or in
any other manner, the result will be the same. If we suppose
particles to be brought together at the centre equally from all