lie. So we must clearly look for something analogous in the case of
water. But here we can find no such single mass, as in the case of the
other elements, except the sea. River water is not a unity, nor is
it stable, but is seen to be in a continuous process of becoming
from day to day. It was this difficulty which made people regard the
sea as the origin and source of moisture and of all water. And so we
find it maintained that rivers not only flow into the sea but
originate from it, the salt water becoming sweet by filtration.
But this view involves another difficulty. If this body of water
is the origin and source of all water, why is it salt and not sweet?
The reason for this, besides answering this question, will ensure
our having a right first conception of the nature of the sea.
The earth is surrounded by water, just as that is by the sphere of
air, and that again by the sphere called that of fire (which is the
outermost both on the common view and on ours). Now the sun, moving as
it does, sets up processes of change and becoming and decay, and by
its agency the finest and sweetest water is every day carried up and
is dissolved into vapour and rises to the upper region, where it is
condensed again by the cold and so returns to the earth. This, as we
have said before, is the regular course of nature.
Hence all my predecessors who supposed that the sun was nourished by
moisture are absurdly mistaken. Some go on to say that the solstices
are due to this, the reason being that the same places cannot always
supply the sun with nourishment and that without it he must perish.
For the fire we are familiar with lives as long as it is fed, and
the only food for fire is moisture. As if the moisture that is
raised could reach the sun! or this ascent were really like that
performed by flame as it comes into being, and to which they
supposed the case of the sun to be analogous! Really there is no
similarity. A flame is a process of becoming, involving a constant
interchange of moist and dry. It cannot be said to be nourished
since it scarcely persists as one and the same for a moment. This