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

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