CHAPTER XV. OF EARTHQUAKES.
Thales and Democritus assign the cause of earthquakes to water. The Stoics say that it is a moist vapor contained in the earth, making an irruption into the air, that causes the earthquake. Anaximenes, that the dryness and rarity of the earth are the cause of earthquakes, the one of which is produced by extreme drought, the other by immoderate showers. Anaxagoras, that the air endeavoring to make a passage out of the earth, meeting with a thick superficies, is not able to force its way, and so shakes the circumambient earth with a trembling. Aristotle, that a cold vapor encompassing every part of the earth prohibits the evacuation of vapors; for those which are hot, being in themselves light, endeavor to force a passage upwards, by which means the dry exhalations, being left in the earth, use their utmost endeavor to make a passage out, and being wedged in, they suffer various circumvolutions and shake the earth. Metrodorus, that whatsoever is in its own place is incapable of motion, except it be pressed upon or drawn by the operation of another body; the earth being so seated cannot naturally be moved, yet divers parts and places of the earth may move one upon another. Parmenides and Democritus, that the earth being so equally poised hath no sufficient ground why it should incline more to one side than to the other; so that it may be shaken, but cannot be removed. Anaximenes, that the earth by reason of its latitude is borne upon by the air which presseth upon it. Others opine that the earth swims upon the waters, as boards and broad planks, and by that reason is moved. Plato, that motion is by six manner of ways, upwards, downwards, on the right hand and on the left, behind and before; therefore it is not possible that the earth should be moved in any of these modes, for it is altogether seated in the lowest place; it therefore cannot receive a motion, since there is nothing about it so peculiar as to cause it to incline any way; but some parts of it are so rare and thin that they are capable of motion. Epicurus, that the possibility of the earth's motion ariseth from a thick and aqueous air under the earth, that may, by moving or pushing it, be capable of quaking; or that being so compassed, and having many passages, it is shaken by the wind which is dispersed through the hollow dens of it.
CHAPTER XVI. OF THE SEA, AND HOW IT IS COMPOSED, AND HOW IT BECOMES TO THE TASTE BITTER.
Anaximander affirms that the sea is the remainder of the primogenial humidity, the greatest part of which being dried up by the fire, the influence of the great heat altered its quality. Anaxagoras that in the beginning water did not flow, but was as a standing pool; and that it was burnt by the movement of the sun about it, by which the oily part of the water being exhaled, the residue became salt. Empedocles, that the sea is the sweat of the earth heated by the sun. Antiphon, that the sweat of that which was hot was separated from the rest which were moist; these by seething and boiling became bitter, as happens in all sweats. Metrodorus, that the sea was strained through the earth, and retained some part of its density; the same is observed in all those things which are strained through ashes. The schools of Plato, that the element of water being compacted by the rigor of the air became sweet, but that part which was expired from the earth, being enfired, became of a brackish taste.
CHAPTER XVII. OF TIDES, OR OF THE EBBING AND FLOWING OF THE SEA.
Aristotle and Heraclides say, they proceed from the sun, which moves and whirls about the winds; and these falling with a violence upon the Atlantic, it is pressed and swells by them, by which means the sea flows; and their impression ceasing, the sea retracts, hence they ebb. Pytheas the Massilian, that the fulness of the moon gives the flow, the wane the ebb. Plato attributes it all to a certain balance of the sea, which by means of a mouth or orifice causes the tide; and by this means the seas do rise and flow alternately. Timaeus believes that those rivers which fall from the mountains of the Celtic Gaul into the Atlantic produce a tide. For upon their entering upon that sea, they violently press upon it, and so cause the flow; but they disemboguing themselves, there is a cessation of the impetuousness, by which means the ebb is produced. Seleucus the mathematician attributes a motion to the earth; and thus he pronounceth that the moon in its circumlation meets and repels the earth in its motion; between these two, the earth and the moon, there is a vehement wind raised and intercepted, which rushes upon the Atlantic Ocean, and gives us a probable argument that it is the cause the sea is troubled and moved.