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meteorologists。 They believed that the sun did not pass below the
earth； but round its northern part； and that it was the height of this
which obscured the sun and caused night。
So much to prove that there cannot be sources of the sea and to
explain its observed flow。
2
We must now discuss the origin of the sea； if it has an origin；
and the cause of its salt and bitter taste。
What made earlier writers consider the sea to be the original and
main body of water is this。 It seems reasonable to suppose that to
be the case on the analogy of the other elements。 Each of them has a
main bulk which by reason of its mass is the origin of that element；
and any parts which change and mix with the other elements come from
it。 Thus the main body of fire is in the upper region； that of air
occupies the place next inside the region of fire； while the mass of
the earth is that round which the rest of the elements are seen to
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
cannot be true of the sun； for if it were nourished like that； as they
say it is； we should obviously not only have a new sun every day； as
Heraclitus says； but a new sun every moment。 Again； when the sun
causes the moisture to rise； this is like fire heating water。 So； as
the fire is not fed by the water above it； it is absurd to suppose
that the sun feeds on that moisture； even if its heat made all the
water in the world evaporate。 Again； it is absurd； considering the
number and size of the stars； that these thinkers should consider
the sun only and overlook the question how the rest of the heavenly
bodies subsist。 Again； they are met by the same difficulty as those
who say that at first the earth itself was moist and the world round
the earth was warmed by the sun； and so air was generated and the
whole firmament grew； and the air caused winds and solstices。 The
objection is that we always plainly see the water that has been
carried up coming down again。 Even if the same amount does not come
back in a year or in a given country； yet in a certain period all that
has been carried up is returned。 This implies that the celestial
bodies do not feed on it； and that we cannot distinguish between
some air which preserves its character once it is generated and some
other which is generated but becomes water again and so perishes； on
the contrary； all the moisture alike is dissolved and all of it
condensed back into water。
The drinkable； sweet water； then； is light and is all of it drawn
up： the salt water is heavy and remains behind； but not in its natural
place。 For this is a question which has been sufficiently discussed （I
mean about the natural place that water； like the other elements； must
in reason have）； and the answer is this。 The place which we see the
sea filling is not its natural place but that of water。 It seems to
belong to the sea because the weight of the salt water makes it remain
there； while the sweet； drinkable water which is light is carried
up。 The same thing happens in animal bodies。 Here； too； the food
when it enters the body is sweet； yet the residuum and dregs of liquid
food are found to be bitter and salt。 This is because the sweet and
drinkable part of it has been drawn away by the natural animal heat
and has passed into the flesh and the other parts of the body
according to their several natures。 Now just as here it would be wrong
for any one to refuse to call the belly the place of liquid food
because that disappears from it soon； and to call it the place of
the residuum because this is seen to remain； so in the case of our
present subject。 This place； we say； is the place of water。 Hence
all rivers and all the water that is generated flow into it： for water
flows into the deepest place； and the deepest part of the earth is
filled by the sea。 Only all the light and sweet part of it is
quickly carried off by the sun； while herest remains for the reason we
have explained。 It is quite natural that some people should have
been puzzled by the old question why such a mass of water leaves no
trace anywhere （for the sea does not increase though innumerable and
vast rivers are flowing into it every day。） But if one considers the
matter the solution is easy。 The same amount of water does not take as
long to dry up when it is spread out as when it is gathered in a body；
and indeed the difference is so great that in the one case it might
persist the whole day long while in the other it might all disappear
in a moment…as for instance if one were to spread out a cup of water
over a large table。 This is the case with the rivers： all the time
they are flowing their water forms a compa