But if
bodies of another kind go and attack them [i.e. the small
particles], the latter continue to be dissolved until, being
completely forced back and dispersed, they make their escape to
their own kindred, or else, being overcome and assimilated to the
conquering power, they remain where they are and dwell with their
victors, and from being many become one. And owing to these
affections, all things are changing their place, for by the
motion of the receiving vessel the bulk of each class is
distributed into its proper place; but those things which become
unlike themselves and like other things, are hurried by the
shaking into the place of the things to which they grow like.
Now all unmixed and primary bodies are produced by such causes
as these. As to the subordinate species which are included in the
greater kinds, they are to be attributed to the varieties in the
structure of the two original triangles. For either structure did
not originally produce the triangle of one size only, but some
larger and some smaller, and there are as many sizes as there are
species of the four elements. Hence when they are mingled with
themselves and with one another there is an endless variety of
them, which those who would arrive at the probable truth of
nature ought duly to consider.
Unless a person comes to an understanding about the nature and
conditions of rest and motion, he will meet with many
difficulties in the discussion which follows. Something has been
said of this matter already, and something more remains to be
said, which is, that motion never exists in what is uniform. For
to conceive that anything can be moved without a mover is hard or
indeed impossible, and equally impossible to conceive that there
can be a mover unless there be something which can be moved-motion
cannot exist where either of these are wanting, and for these to
be uniform is impossible; wherefore we must assign rest to
uniformity and motion to the want of uniformity. Now inequality
is the cause of the nature which is wanting in uniformity; and of
this we have already described the origin. But there still
remains the further point-why things when divided after their
kinds do not cease to pass through one another and to change
their place-which we will now proceed to explain. In the
revolution of the universe are comprehended all the four
elements, and this being circular and having a tendency to come
together, compresses everything and will not allow any place to
be left void. Wherefore, also, fire above all things penetrates
everywhere, and air next, as being next in rarity of the
elements; and the two other elements in like manner penetrate
according to their degrees of rarity. For those things which are
composed of the largest particles have the largest void left in
their compositions, and those which are composed of the smallest
particles have the least. And the contraction caused by the
compression thrusts the smaller particles into the interstices of
the larger. And thus, when the small parts are placed side by
side with the larger, and the lesser divide the greater and the
greater unite the lesser, all the elements are borne up and down
and hither and thither towards their own places; for the change
in the size of each changes its position in space. And these
causes generate an inequality which is always maintained, and is
continually creating a perpetual motion of the elements in all
time.
In the next place we have to consider that there are divers
kinds of fire. There are, for example, first, flame; and
secondly, those emanations of flame which do not burn but only
give light to the eyes; thirdly, the remains of fire, which are
seen in red-hot embers after the flame has been extinguished.
There are similar differences in the air; of which the brightest
part is called the aether, and the most turbid sort mist and
darkness; and there are various other nameless kinds which arise
from the inequality of the triangles. Water, again, admits in the
first place of a division into two kinds; the one liquid and the
other fusile. The liquid kind is composed of the small and
unequal particles of water; and moves itself and is moved by
other bodies owing to the want of uniformity and the shape of its
particles; whereas the fusile kind, being formed of large and
uniform particles, is more stable than the other, and is heavy
and compact by reason of its uniformity. But when fire gets in
and dissolves the particles and destroys the uniformity, it has
greater mobility, and becoming fluid is thrust forth by the
neighbouring air and spreads upon the earth; and this dissolution
of the solid masses is called melting, and their spreading out
upon the earth flowing. Again, when the fire goes out of the
fusile substance, it does not pass into vacuum, but into the
neighbouring air; and the air which is displaced forces together
the liquid and still moveable mass into the place which was
occupied by the fire, and unites it with itself. Thus compressed
the mass resumes its equability, and is again at unity with
itself, because the fire which was the author of the inequality
has retreated; and this departure of the fire is called cooling,
and the coming together which follows upon it is termed
congealment. Of all the kinds termed fusile, that which is the
densest and is formed out of the finest and most uniform parts is
that most precious possession called gold, which is hardened by
filtration through rock; this is unique in kind, and has both a
glittering and a yellow colour. A shoot of gold, which is so
dense as to be very hard, and takes a black colour, is termed
adamant. There is also another kind which has parts nearly like
gold, and of which there are several species; it is denser than
gold, and it contains a small and fine portion of earth, and is
therefore harder, yet also lighter because of the great
interstices which it has within itself; and this substance, which
is one of the bright and denser kinds of water, when solidified
is called copper. There is an alloy of earth mingled with it,
which, when the two parts grow old and are disunited, shows
itself separately and is called rust. The remaining phenomena of
the same kind there will be no difficulty in reasoning out by the
method of probabilities.
