ON THE ORIGIN AND CAUSES OF SUBTERRANEAN THINGS, BOOK I

the heat of the sun enters into the depths of the caverns, which it warms and contains within its embrace. As if such great heat from the sun—which could warm water to the point of boiling—could not have made the soft earth hard over such a long period of time. And as if all the mountains near the valleys, from which hot waters burst forth, have rare porous earth just because one or two happen to have it. And why would soft earth not harden in a few days under such intense solar heat? And if that porosity is not present in the mountains, because they are for the most part rocky—but let us grant that a certain softness and porosity exists in them through which the sun’s heat might penetrate under the earth—it would certainly warm the waters when it ascends to the summer sign, but would not warm them when, with a reversed course, it approaches the winter sign. But in the wintertime, such springs are no less hot than in the summer, nor does the approach and departure of the sun change their heat. Therefore, the sun does not generate hot waters. What then would generate them within the earth? It hardly warms any lake in the hottest region to the point of boiling.

Another opinion is that of those who say that wind, driven violently into the bowels of the earth and thus somehow confined there, causes the heat, and by pressing more sharply upon the waters, warms them. Those people, however, do not notice that even if the wind could warm the waters, it could not be contained. For as soon as the caverns pour out the water, they emit the wind along with it. The entire body of hot water, once poured out, would be followed by cold water, which we do not see happen. Certainly, anyone who reads the writers of historical accounts has no doubt that in Italy, hot waters have flowed from the same springs for many centuries. But neither can an inflamed spirit warm the waters to such a degree, because its heat is extinguished by their coldness, nor can it endure for a long time without fuel. Since they themselves say nothing about this, we understand that they held a false opinion concerning hot waters.

A third opinion is related to this one: that waters are warmed by being dashed against rocks due to varied and violent motion. This must be rooted out of people's minds. Metallurgists can certainly know by daily experiment that subterranean waters, no matter how variably and precipitously they flow, do not become hot for that reason. No less so for others who consider that some rivers or streams go under the earth, and return not hot, but cold. For example, the Alpheus a river in Greece, after being submerged on the Peloponnesian shore, completes a course under the sea over a very long distance and emerges again in the Syracusan territory, where its spring is named Arethusa, and it comes out cold. Therefore, motion is not the cause of the heat of the waters.

A fourth opinion is that there is an extreme heat within the earth in those places that bubble with hot waters, and that this is their cause. But those who think so do not agree among themselves. For some of them think that the waters are warmed while enclosed in caverns; others think that when the earth, soaked with waters, has been heated, it exhales hot vapors from which hot waters arise. But subterranean...