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Besides, even if one leaves out of account water so produced and considers only the daily supply of
water already existing, this does not act as a source of rivers by segregating into subterranean lakes, as
it were, in the way some people maintain: the process is rather like that in which small drops form in
the region above the earth, and these again join others, until rain water falls in some quantity; similarly
inside the earth quantities of water, quite small at first, collect together and gush out of the earth, as it
were, at a single point and form the sources of rivers. A practical proof of this is that when men make
irrigation works they collect the water in pipes and channels, as though the higher parts of the earth
were sweating it out. So we find that the sources of rivers flow from mountains, and that the largest
and most numerous rivers flow from the highest mountains. Similarly the majority of springs are in the
neighborhood of mountains and high places, and there are few sources of water in the plains except
rivers. For mountains and high places act like a big sponge overhanging the earth and make the water
drip through and run together in small quantities in many places. For they receive the great volume of
rain water that falls (it makes no difference whether a receptacle of this sort is concave and turned up
or convex and turned down: it will contain the same volume whichever it is); and they cool the vapor
as it rises and condense it again to water.
Thus the argument is repeated and clarified by contrasting it with yet another theory which,
as he explains, holds that rivers originate from preexisting or primal water stored in under-
ground lakes. Reference is undoubtedly made here to the Tartarus theory of his teacher Plato
(1975; 1993, 111 d, ff.), which Aristotle discusses and refutes more thoroughly later on (see
355 b,38). The passage is noteworthy in that it indicates that there were others who held this
view. But this Tartarus, which also appears in Homer's poetry, is more a throwback to Greek
mythology rather than natural philosophy and its discussion is beyond the present scope.
Aristotle concludes the paragraph by summarizing once again his own opinion: springs and
the sources of rivers result both from rainfall and from condensation inside the Earth.
On why the sea does not overflow
Beside the origin of rivers, Aristotle also concerned himself with the problem why the sea
does not overflow, even though all rivers flow into it (Aristotle, 1952, II 355 b,15).
The place occupied by the sea is, as we say, the proper place of water, which is why all rivers and all
the water there is run into it: for water flows to the deepest place, and the sea occupies the deepest place
on earth. But one part of it is all quickly drawn up by the sun, while the other for the reasons given
is left behind. The old difficulty why so great an amount of water disappears (for the sea becomes no
larger even though innumerable rivers of immense size are flowing into it every day) is quite a natural
one to ask, but not difficult to answer with a little thought. For the same amount of water does not take
the same time to dry up if it is spread out as if it is concentrated in a small space: the difference is so
great that in the one case it may remain for a whole day, in the other, if for instance one spills a cup of
water over a large table, it will vanish as quick as thought. This is what happens with rivers: they go on
flowing in a constricted space until they reach a place of vast area when they spread out and evaporate
rapidly and imperceptively.
He calls it an “old difficulty,” so it must have been a problem of long standing in Greek
philosophy; indeed as seen earlier, Anaximander had already thought about it and had
concluded that the sea may eventually dry up altogether. While Aristotle seems to have been
the first on record to resolve the issue successfully by providing the correct explanation, it
was considered elsewhere as well.
For instance, it appears to have been of concern in ancient China (see Lin, 1949). In the
third century BCE during the Zhou (or Chou) dynasty, in the chapter “Autumn Floods”,
Zhuang Zi (or Chuangtse, d. 275 BCE), raised the issue, as follows.
There is no body of water beneath the canopy of heaven which is greater than the ocean. All streams
pour into it without cease, yet it does not overflow. It is being continually drained off at the Tail-Gate,
yet it is never empty. Spring and autumn bring no change; floods and droughts are equally unknown.
