Geoscience Reference
In-Depth Information
Some of them (natural philosophers) say that the sea is the leftover of the original moisture. As the
region around the earth was wet, the first of that moisture was evaporated by the sun and became the
winds, and from it the turnings of the sun and of the moon as well; thus, as the turnings are caused by
the same vapors and by their exhalations, it becomes then the provider of the same (moisture) for those
revolving around them. The part of it (the moisture) that is left behind in the hollow places is the sea;
therefore, it decreases, as it is continually evaporated by the sun, and eventually it will perhaps have to
be dry. Anaximander and Diogenes (of Apollonia) arrived at this view, thus reports Theophrastos.
Anaximander's opinion on what happens to this continual evaporation was summarized
by Hippolytus, a Christian writer of the early third century, who died in 235 CE; in his
Refutation
(see Mansfeld, 1992), Hippolytus described it as follows (Diels, 1879, p. 560,
6, 7; 1961, p. 84, 6, 7).
Winds are generated when the finest vapors of the air are separated off and whenever they are put into
motion as they gather; rains are generated from the vapor that is released upward from the earth by the
sun.
These two passages indicate that Anaximander considered the sea to be the remainder of
the original water around the Earth; the evaporation from the sea is the cause, instead of the
result, of the winds and also the cause of the rains. There is no specific mention of streams.
Anaximander did not assume, as Thales did, that the Earth floats on water, which would then
flow upward to the surface to feed springs and streams; instead, he is known to have posited
that the Earth does not rest on anything and that it is suspended in the sky in some sort of
equilibrium, because it is equidistant from everything on all sides. Therefore, it is unlikely
that he would have assumed that the sea feeds the streams by some upward filtration, as
asserted by Thales and Hippon. Rather, it would seem more natural in his scheme that it is
a different source of water, perhaps rainwater, which is feeding the streams that flow into
the sea. On the other hand, it is clear that he did not think that all the evaporated water ends
up in streams and rivers, because the sea is gradually drying out; thus, he definitely did
not propose a closed cycle. In any event, he seems to have started, or at least stimulated, a
productive line of thought, as can be seen from the views of Xenophanes.
Xenophanes of Colophon (
c
. 570
−
460 BCE) was probably in his prime
c
. 530 BCE,
which is roughly some 35 years after Anaximander. According to Aetius (in Diels, 1879,
p. 371, 4; 1961, p. 125, III, 4, 4), a doxographer who probably lived in the first century CE
(Mansfeld and Runia, 1997), Xenophanes said that
. . . what happens in the sky is caused by the heat of the sun; for, when the moisture is drawn out of
the sea, the sweet part, which is distinguished by its fine texture, forms a cloud, and drips out as rain
by compression like that of felt, and the winds vaporize it around. And he wrote emphatically
(an actual fragment follows in verse, Diels,1961, p. 136)
The sea is the source of the water, the source of the wind. For in the clouds, neither would the force of
the wind, which blows outward, originate without the great sea, nor the flowing of the streams, nor the
rainwater from the sky; but the great sea is the generator of the clouds, winds and streams....
Regarding the saltiness of the sea, the opinion of Xenophanes is described by Hippolytus
(Diels, 1879, p. 565, 14, 4; 1961, p. 122, 33, 14, 4) as follows.
The sea is salty, he says, because of the many admixtures which flow together into it.
All this indicates that Xenophanes had some idea of the hydrologic cycle, as we now know
it. He not only includes streams in his description, but he specifies that together with the
winds, with the rain and with the clouds, the streams are caused by the evaporation from
the sea. The only possible interpretation is that this occurs indirectly through the rain on
the land surface. This is further supported by his explanation that the saltiness of the sea is
