Intense and swift are the actions that cold and heat perform in the earth. For in summer the heat of the sun warms the surface of the earth, and since two contrary things do not endure to remain in the same place, the cold flies before the heat to the bowels of the earth and that makes the water which it finds under the earth cold, and on that account the water of the wells is cold in summer. For the same reason, on account of the great distance of the sun from us in winter,63 the cold gains strength then on the surface of this whole earth, and sends the heat flying in before it to the interior of the earth. Therefore the water of the wells is warm in winter; and when, in the summer, that cold is in the middle of the earth in all its strength, it concentrates and compresses itself there, since the solidity and firmness of the earth does not allow it to escape, and the further in it is, the greater is its power and strength. In the winter when the cold of the earth's surface sends the heat into the centre of the earth, and finds the prisoner inside before it, i.e., the cold of the centre of the earth, they act upon each other, and each of them seeks to destroy the other, and the earth shakes; and it is to that shaking that terrae motus, i.e., earthquake64, is applied. It results from that shock that the earth is cut and broken and great wind accompanied by thunder and noise comes forth from that breach, and the wind carries with it sods of earth and stones, and no person, animal, castle, or any other solid thing that one of those stones would strike, could escape its passing through them.
It often happens at a time of terrae motus that the sun is darkened; and the cause of that darkness is that the strong wind, that comes from that rupture of the earth, blows much dust and sods with strength and force from it up into the air. And that dust is like a cloud between the earth and the sun, and cuts off the light of the sun from the surrounding nations.
At another time the terrae motus breaks the earth under the sea, and the wind that comes out of the water blows up into the air and makes the sea rage in a terrible manner.65 The same shock tears hills and mountains when there is a disturbance beneath them, so that it leaves deep dark crevices which appear bottomless.
Moreover, waters taste differently according as they are situated in different places. Although all waters have the same substance, they adopt an accidental peculiarity according to the taste of the earth in which they are situated. Consequently, the water that is in a stony, sandy place has a sweet taste, and the water that is in salt earth has a salty taste, and the water that is in clay soil has a flat taste, and the water that is in acid earth, where there are stones of
p.148sulfur or alum, or a place where there is a brass or copper mine or other acids, that water has a bitter taste; therefore, in accordance with the accidental peculiarity of the taste of the soil in which the waters are, does the water change the accident of taste.
Also, when the rivers that flow on the surface of the earth encounter weak, movable soil they pierce through it and make secret paths for themselves in it beneath the earth, until they meet immovable earth that does not let them pass to this side or that. Since, when, they thus come in conflict below, the earth breaks overhead, and they are converted into wells, according to the greatness or smallness of the underground streams whence they come, or according to the quantity of the rain, from whence the streams come, since it is in accordance with that that the wells fill or dry up.
The cause of the saltiness of the sea is its own antiquity and the constant beating of the waves around its stones, and the course of the sun being always above it, and because the sweetest parts of the water are driven from it by the heat of the sun.66 For the heat of the sun draws the most volatile and sweetest part of the water of the sea up into the clouds of the air, and from that are made the dew and the rain and the snow and the hailstones and every other phenomenon from above. It leaves below the heaviest, most solid, most material, and sourest portion. From its similar nature, human urine is sour, for the same action as is performed by the sun upon the sea, is performed by the bile67 upon the urine, as it filters it and extracts the volatile parts from it.
From the same cause water that receives much boiling becomes bitter, as the heat of the fire vapourises it. When that salt seawater receives much boiling on the fire, or from the sun in warm countries, it becomes crystallised68 and solidified, and adopts the nature of the earth, and that is the salt we use. That effect is produced by the excessive boiling, caused by fire or by the sun vapourising them i.e., the waters. They are thus strained, and become solid and converted into the nature of the earth in accordance with (their) solidity. And sometimes fresh water, and particularly the water of rivers, is bound by the intensity of the cold and converted into ice. The natural heat that is in the sea, and the fact that it is still, does not permit it to take that binding upon itself from the cold, because it is the nature of cold to bind everything that flows and the nature of heat to dissolve every bound thing, as the philosophers say.