Aristotle
ei(=s koi/ranos."]--p. 1076, a. 4).
IV.
DE COELO.
Book I.
CH. 1.--The science of Nature has for its principal object--Bodies,
Magnitudes, and the various affections and movements of Bodies and
Magnitudes; also the beginnings or principles of this sort of
Essence. The Continuous is that which is divisible into parts
perpetually divisible: and Body is that which is divisible in every
direction. Of magnitudes, some (lines) are divisible only in one
direction; others (planes) only in two directions; others again
(bodies) in three directions. This is the maximum: there is no other
magnitude beyond; for three are all, and to say "in three directions"
is the same as to say "in all directions." As the Pythagoreans say,
The Universe and All Things are determined by Three: in End, Middle,
and Beginning, lies the number of the Universe, or the Triad. We have
received these as laws from nature, and we accordingly employ this
number (Three) for solemnities in honour of the Gods. Moreover, we
apply our predicates on the same principle; for we call Two, and The
Two--Both, but we do not call them all. Three is the first number to
which we apply the predicate All. Herein (as was observed before) we
follow the lead of Nature herself. Since therefore these three
phrases--All Things, The Universe, The Perfect or Complete--do not
specifically differ from each other, but are distinguished only in
respect of the matter or occasions on which they are applied. Body is
the only kind of magnitude which can be declared Perfect or Complete,
that is, All; for it is the only magnitude determined or defined by
the Three. Being divisible in three directions, it is divisible every
way; other magnitudes are divisible either only in one way or only in
two. Magnitudes are both divisible and continuous according to the
number by which they are designated--continuous in one direction, in
two, in three, or all. All divisible magnitudes are also continuous:
whether all continuous magnitudes are divisible, is not yet clear.
But what _is_ clear is--that there is no upward transition to a
higher genus beyond Body, as there is from line to surface, and from
surface to Body. If there were, Body would not be perfect or complete
as a magnitude; for the transition would be made at the point of
deficiency; but the perfect or complete can have no deficiency: it
stretches every way. Such is each body included as a part in the
universe: it has dimensions in every direction. Yet each is
distinguished from its neighbour by contact, and each therefore in a
certain sense is many. But the Universe ([Greek: to\ pa=n]) including
all these parts is of necessity perfect and complete; extending not
merely in one way, and in another way not, but [Greek: pa/ntê|], as
the word literally means (ss. 1-4).
CH. 2.--Respecting the nature of the Universe, we shall enquire
presently whether in the aggregate it be infinite or of finite
magnitude. But first let us speak about its different constituent
species, proceeding on the following basis. I affirm that all natural
bodies and magnitudes are _per se_ locally moveable; and that Nature
is to them a beginning or principle of motion. Now all Local Motion
(known by the name of [Greek: phora/]) is either Rectilinear or
Circular, or compounded of the two; for these two are the only simple
motions, by reason that the only two simple magnitudes are the
rectilinear and the circular. The circular is motion round the
Centre; the rectilinear is motion either downwards towards the centre
or upwards from the centre. These three are the only simple modes of
motion or currents: as I said in the last chapter that body was made
complete in the number three, so also the motion of body is made
complete in the number three. Now, as there are some bodies (such as
fire, earth, and their cognates) which are simple (_i.e._ which have
in themselves a natural beginning or principle of motion), and others
which are compounds of these, so also there must be simple motions
belonging to the former and compound motions belonging to the latter;
such compound motions being determined by the preponderant element
therein. Since, therefore, circular motion is a simple mode of
motion, and since simple modes of motion belong only to simple
bodies, there must of necessity be a particular variety of simple
body, whose especial nature it is to be carried round in circular
motion. By violence, indeed, one body might be moved in a mode
belonging to another; but not by nature. Moreover, since motion
against nature is opposite to motion conformable to nature, and since
each mode has one single opposite, simple circular motion, if it be
not conformable to the nature of this body, must be against its
nature. If then the body rotating in a circle be fire or any of the
other elements, its natural mode of motion must be opposite to
circular motion. But each thing has only one opposite; and up and
down are each other's opposites. If then the body which rotates in a
circle rotates thus against nature, it must have some other mode of
motion conformable to nature. But this is impossible: for, if the
motion conformable to its nature be motion upwards, the body must be
fire or air; if motion downwards, the body must be earth or water
(and there is no other simple mode of motion that it can have).
Moreover, its rotatory motion must be a first motion; for the perfect
is prior in nature to the imperfect. Now the circle is perfect; but
no straight line is perfect: neither an infinite straight line, for
in order to be perfect, it must have an end and a boundary; nor any
finite straight line, for each has something without it and may be
prolonged at pleasure. So that, if motion first by nature belong to a
body first by nature, if circular motion (as being perfect) be prior
to rectilinear motion, and if rectilinear motion belong to a first or
a simple body, as we see both in fire and in earth,--we may be sure
_à fortiori_ that circular motion belongs to a simple body, and that
there is, besides the four elements here, prior to them and more
divine than them, a different body cf special nature and essence.
Indeed, since circular motion is against the nature of these four
elements, there must be some other different body to whose nature it
is conformable. There must thus be some simple and primary body,
whose nature it is to be carried round in a circle, as earth is
carried downwards and fire upwards. On the assumption that the
revolving bodies revolved against their own nature, it would be
wonderful and even unreasonable that this one single mode of motion,
being thus contrary to nature, should be continuous and eternal; for
in all other things we see that what is contrary to nature dies away
most speedily. Now, if the revolving body were fire, as some affirm,
the revolving motion would be just as much contrary to its nature as
motion downwards; for the natural motion of fire is upwards or away
from the centre. Reasoning from all these premisses, we may safely
conclude that, distinct from all these bodies which are here around
us, there exists a body whose nature is more honourable in proportion
to its greater distance from us here (ss. 1-13).
CH. 3.--We plainly cannot affirm that every body is either heavy or
light: meaning by heavy, that which is carried by its nature
downwards or towards the centre; by light, that which is carried by
its nature upwards or away from the centre. Heaviest (or earth) is
that which underlies all other downward moving bodies, lightest
(fire) is that which floats above all upward moving bodies. Air and
water are both light and heavy, relatively, but relatively to
different terms of comparison; thus, water is heavy as compared to
air and fire, light as compared to earth. But that body whose nature
it is to revolve in a circle, cannot possibly have either heaviness
or levity; for it cannot move in a right line, either upwards or
downwards, nor either by nature or against nature. Not by nature,
for, in that case, it must be identical with some one of the four
elements; not against nature, because, if it moved upwards against
nature, this would prove that motion downwards was conformable to its
nature, and it would thus be identical with earth: we have already
seen that, if a body moves upwards against nature, it must move
downwards according to nature, and _vice versâ_. Now the same natural
motion which belongs to any body as a whole, belongs also to its
minute fragments (to the whole earth and to any of its constituent
clods). Accordingly the revolving body in its local movement of
revolution cannot possibly be dragged in any other direction, either
upward or downward,--neither the whole nor any portion thereof. It is
alike reasonable to conceive it as ungenerable, indestructible,
incapable both of increase and of qualitative change ([Greek:
a)nauxe\s kai\ a)nalloi/ôton]). It cannot be generated, because
every thing generated comes out of a substratum and an opposite, into
which it relapses on being destroyed. Now the revolving body has no
opposite; for we have already seen that opposite bodies have their
currents of motion opposite, and there is no current of motion
opposite to that of circular rotation. Nature has rightly excepted
this ungenerable and indestructible substance from the action of
contraries, in which generation and destruction occur. It is also
incapable of increase or diminution, because these processes take
place through the accession of new cognate materials; and in this
case there are none such. It is farther incapable of qualitative
change, because this always implies the being affected favourably or
unfavourably ([Greek: pa/thos]); and this last never takes place, in
plants or in animals, without some increase or diminution in quantity
(ss. 1-5).
This Celestial Substance is thus eternal, ungenerable,
indestructible, noway increased nor diminished, neither growing old
nor capable of disturbing affections nor changeable in quality.
Herein the evidence of reason and that of phenomena concur. For all
men, Hellenes and Barbarians, have some belief respecting the Gods,
and all who believe Gods to exist assign to the divine nature the
uppermost place in the Kosmos; an immortal place going naturally
along with immortal persons. Our perceptions confirm this
sufficiently, at least when we speak with reference to human belief.
For not the smallest change has ever been observed in the celestial
substance, throughout all past time. Under these impressions, the
ancients gave to it the name which it now bears; for the same
opinions suggest themselves to us not once, nor twice, but an
infinite number of times**. Hence the ancients, regarding the First
Body as something distinct from Fire, Earth, Air, or Water, called
the uppermost place Æther, from its being always running ([Greek:
a)po\ tou= thei=n a)ei/]), the adverbial designation being derived
from eternal duration. Anaxagoras employs this name improperly: he
calls Fire by the name of Æther (s. 6).
It is plain, from all we have said, that the simple bodies cannot be
more in number than those just indicated; for a simple body must of
necessity have a simple mode of motion, and there are only three
simple modes of motion--one circular and two rectilinear, one of
these being from the centre, the other towards the centre (s. 7).
CH. 4.--That Circular Rotation has no motion opposed to it, may be
shown by several different arguments. If there were any, it would
certainly be rectilinear motion; for convex and concave, though each
respectively opposed to the other, are, when both put together,
opposed as a couple to rectilinear motion. But each variety of
rectilinear motion has another variety of rectilinear motion opposed