Underground Rivers - University of New Mexico

Chapter 12 -- Superterranean Metrics
Mediterranean to be 1.9 million square kilometers -- actually, it’s 2.5 -- Halley calculated daily
evaporation to be 5.3 billion metric tons. (Lest the value seem unduly large, it corresponds to
slightly less than 3 millimeters/day. Modern meteorological records averaged over a full year
indicate about half that.)
By extrapolating from the estimated flow of the Thames, Halley concluded that evaporation from
the Mediterranean exceeds its river inflow and again extrapolated that there is sufficient
evaporation from the world's oceans to supply all the rivers and springs.
To bring his numbers into balance, he reported to the Royal Society in 1690 that some of the
vapor from the sea swept against the high mountain tops “gleets down by the crannies” and
enters into caverns from where it flows back to the sea. Mountains thus act as “external
alembics” to distill fresh water for the benefit of man “like so many veins in the microcosm.”
An Estimation of the Quantity of Vapour Raised out of the Sea, and the Cause of Springs (1687)
illustrates the caverns and rivers.
Halley wasn't willing to place his entire bet with the rainfall hypothesis. To explain how springs
continued to flow during periods when there was no rain,
Those Vapors therefore that are raised copiously in the Sea, and by the Winds are carried over
the low Land in those Ridges of Mountains, are there compelled by the stream of the Air to
mount up with it to the tops of the Mountains, where the Water presently precipitates, gleeting
down by the Crannies of the stone; and part of the Vapour entering into the Caverns of the
Hills, the Water thereof gathers as in an Alembick into the Basons of stone it finds, which being
once filled, all the overplus of Water that comes thither runs over by the lowest place, and
breaking out of the sides of the Hills, forms single Springs.
I doubt not but this Hypothesis is more reasonable than that of those who derive all Springs...
from a Filtration of Percolation of the Sea-waters through certain imaginary Tubes or Passages
within the Earth, wherein they lose their saltness.-- "An Account of the Circulation of the Watery
Vapors of the Sea, and of the Causes of Springs," Philosophical Transactions of the Royal
Society (1686)
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