Underground Rivers - University of New Mexico

Chapter 11 -- Straining the Salt
Democritus (460-370 BC) held that the salinity of the sea is due to the same cause as the
accumulation of salt on the land, like seeking like. As the water flees via secret channels to lakes
and rivers, the sea will become smaller and smaller and finally dry up.
Aristotle (384-322 BC) drew upon them all.
At first the Earth was surrounded by moisture. Then the sun began to dry it up, part of it
evaporated, and is the cause of winds while the remainder formed the seas. So the seas are
being dried up. Others say that the sea is a kind of sweat exuded by the earth when the sun
heats it, and that this explains its saltness, for all sweat is salt. Others say that the saltness is
due to the earth. Just as water strained through ashes becomes salt, so the sea owes its
saltness to the mixture of earth with similar properties.
The fresh water, then, is evaporated, the salt water left. The process is analogous to the
digestion of liquid food. The place occupied by the sea is the natural place of water, and fresh
water evaporates more easily and quickly when it reaches and is dispersed in the sea. The sea
is not salt either because it is a residue left by evaporation or because of an admixture of earth;
nor is it any explanation to call it the sweat of the earth.
Concluding "nor is it any explanation to call it the sweat of the earth" seems odd from a
biologically-inclined philosopher, but to Aristotle's credit, his was the first theory of salt circulation
not reliant on subsurface filtration.
Seneca (3 BC-65 AD) agreed with the early Greeks that marine substances separate. Requoting
from Chapter 3,
The sea water returns by a secret path, and is filtered in its passage back. Being dashed
about as it passes through the endless, winding channels in the ground, it loses its salinity,
and, purged of its bitterness in such a variety of ground as it passes through, it eventually
changes into pure, fresh water.
Unlike his predecessors, however, Seneca was on the lookout for evidence. "The endless,
winding channels in the ground" he believed to be proven by calcareous tuff.
The poet Lucretius Caro (99-55 BC) adopted Aristotelian
explanations in De Rerum Natura. Mt. Etna, Lucretius
suggested, is hollow. As for the source of springs,
The sun drinks some, to quench his natural heat;
And some the winds brush of.
Some passes through the earth, diffused all over,
And leaves its salt behind in every pore;
For all returns through narrow channels freed
And joins where ere fountain shows her head
And thence fine streams in fair meadows play.
“The clouds imbibe much seawater,” as some translations render the leading words. The power
of wind drives together an abundance of clouds and presses the water out.
"And leaves its salt behind in every pore" was an insightful consequence for a Roman poet, but
one not to be carried to logical conclusion until much later.
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