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treatise
On Plants
, which is still formally attributed to Aristotle (1936; II 822b, 25) although
it is known to be spurious, one reads the following.
Rivers which arise under the ground from mountains behave in the same way. For the matter of which
they are composed is rain; and when the water grows large in quantity and is forced into a narrow
channel within, the excess of vapor rises from them, which cuts through the earth by pressure from
within; and in this way springs and rivers make their appearance.
On Plants
became associated with Aristotle's name probably because it was a product of the
Lyceum and because it reflected the teaching at the school he had founded. But contrary to
Aristotle's explanation in the
Meteorologica
, this passage unambiguously asserts that rivers
are composed of rain, and there is no mention of underground condensation. Thus, among
later generations at the Peripatetic School, it appears that it was the rainfall percolation
theory which gained the upper hand, in spite of its original rejection by Aristotle.
To summarize at this point, Greek antiquity produced essentially four competing theories
on the origin of rivers and springs, namely first and foremost, the rainfall percolation theory,
which is the one still held today; in addition, there were the seawater filtration theory and
the underground condensation theory. Finally, there was also the concept, quite likely based
on early popular beliefs and mythology and seemingly less accepted by the philosophers,
that rivers originate from underground reservoirs of primal water.
14.3 The Latin era
14.3.1 The Romans
The Romans are mainly praised for their engineering feats and their accomplishments in law
and public administration. They are less known for their contributions to natural philosophy
and as a result their writings often tend to be dismissed as mere reviews and commentaries
on the Greeks. This may be true in general, but it is an oversimplification. With their practical
orientation, the Romans usually relied more on observation than on speculation, arriving
at interesting insights in some cases. Moreover, for several centuries their writings were
the only source of ancient philosophy available in Western Europe; they are therefore an
indispensable background to understand and trace the thought currents that brought about
the scientific revolution.
The views of Lucretius (
c
. 99-55 BCE) in his work
On Nature
provide a revealing
example of some aspects of natural philosophy in Rome. In the following passage Lucretius
(1924, V, 261) deals with the problem of why the sea does not overflow and with the origin
of springs.
Moreover, there is no need to say how sea, rivers, and springs for ever well up in abundance with fresh
waters and their streams flow unceasing: the great pouring down of waters from all sides makes it clear.
But, bit by bit, whatever comes first of the water is taken off, and the result is that there is no excess
of liquid in the sum total: partly because strong winds sweep the surface and diminish it, as does the
sun on high unraveling it with his rays; partly because it is distributed abroad through all the earth
underneath; for the pungency is strained off, and the substance of the water seeps back, and all meets
at the sources of each river, whence it returns over the earth in a column of sweet water along the path
which has once been cut for it in its liquid course.
A more elaborate but similar account is given in VI, 608-638. In contrast to Aristotle's
explanation, evaporation is not the only reason why the sea does not overflow; seawater also
flows back underground to feed the springs, in accordance with the original theory of Hippon
and Thales. Also in contrast to Aristotle, who only considered the sun (Brutsaert, 1982),
