d when air is overcome and cut up into small pieces, two and a half
parts of air are condensed into one part of water. Let us consider the
matter in another way. When one of the other elements is fastened
upon by fire, and is cut by the sharpness of its angles and sides, it
coalesces with the fire, and then ceases to be cut by them any longer.
For no element which is one and the same with itself can be changed by
or change another of the same kind and in the same state. But so long
as in the process of transition the weaker is fighting against the
stronger, the dissolution continues. Again, when a few small particles,
enclosed in many larger ones, are in process of decomposition and
extinction, they only cease from their tendency to extinction when they
consent to pass into the conquering nature, and fire becomes air and air
water. 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