Meteorology · Book II

Aristotle · a new plain-English translation from the original language

1| But indeed, if rivers come to be and pass away, and the same regions of the earth are not always covered with water, then the sea too must undergo change in the same way. And since the sea is always leaving some places and advancing upon others, it is clear that of the whole earth the same parts are not always sea and the same parts always land, but everything changes over time. We have now stated why it is that the same parts of the earth are not always dry land or navigable, and for what cause this happens; and likewise why some rivers are perennial and others are not. B.

2| Let us now speak about the sea, both what its nature is, and for what cause so great a quantity of water is salty, and further about its coming-to-be from the beginning. Now the ancients, those occupied with theological accounts, provide it with sources, so that they may have principles and roots for earth and sea alike; for they supposed that what was said in this way would be more grand and more solemn, on the ground that this is a great part of the whole, and that the rest of the heaven was constituted around this place and for its sake, as being the most honored thing and a principle. But those who are wiser in human wisdom give it a coming-to-be: for they say that at first the whole region around the earth was moist, and that as it was dried out by the sun, the part that evaporated they say produces winds and the turnings of the sun and moon, while the part left behind is the sea; that is why they suppose it becomes smaller as it dries out, and that in the end it will all be dry someday. Some of them say that as the earth is heated by the sun, a kind of sweat is produced, and that this is why it is salty—for sweat too is salty. Others say that the earth is the cause of the saltiness: for just as water strained through ash becomes salty, in the same way this water too is salty because such earth has been mixed into it.

3| We must consider, on the basis of what already exists, that it is impossible for the sea to have springs. For of the waters around the earth, some happen to be flowing and some standing. Now all the flowing waters are spring-fed; and we have spoken earlier about springs, that one must think of the origin of a spring not as something stored up as if from a vessel, but as something always coming to be into one place and flowing together, being the first thing to arrive there. Of the standing waters, some are collected pools and settlings, such as marshy waters and all that are lake-like, differing from one another in greater or lesser quantity, and some are spring-fed. But all of these latter are man-made — I mean, for example, the so-called well-waters; for the spring must be higher than the whole course of the flow. Hence spring-waters and river-waters flow of their own accord, while these others require the craft that works them. Such, then, and so many are the differences among waters. Given these distinctions, it is impossible for the sea to have springs; for the sea cannot belong to either of these classes — it is neither something flowing in from elsewhere nor something man-made, and all spring-fed waters have one or the other of these features. And we see no standing water occurring of its own accord in so great a quantity from a spring. Further, since there are several seas that do not mix with one another at any point — of which the Red Sea appears to communicate to some small degree with the sea outside the Pillars, while the Hyrcanian and Caspian seas are both separated from it and inhabited all around — their springs would not have gone unnoticed, if they existed anywhere within them.

4| The sea is seen to flow at the narrows, wherever, because of the land enclosing it, it is drawn together from a great expanse into a small one, on account of its swaying to and fro repeatedly. This is imperceptible where the sea has great extent; but where, because of the narrowness of the land, it occupies a small space, the oscillation that is small in the open sea must appear great there. The whole sea within the Pillars of Heracles flows along the hollow of the land, and so does the mass of the rivers; for the Sea of Azov flows into the Black Sea, and this into the Aegean. All the seas beyond these already do this less conspicuously. This happens to those seas because of the multitude of their rivers (for more rivers flow into the Black Sea and the Sea of Azov than into a region many times its size) and because of the shallowness of their depth; for the sea always appears deeper the farther out one goes: the Black Sea is deeper than the Sea of Azov, the Aegean deeper than the Black Sea, the Sicilian Sea deeper than the Aegean; and the Sardinian and Tyrrhenian seas are the deepest of all. The waters beyond the Pillars are shallow because of the mud, and are windless, since the sea there lies as if in a hollow.

5| Just as, in particular cases, rivers are seen to flow down from high places, so too for the whole earth the greatest part of the flow comes from the higher regions toward the north. Hence the waters produced by this outpouring are not deep, while the seas farther out are deeper. As for the north being the higher part of the earth, one sign of this is that many of the ancient students of the heavens were persuaded that the sun does not travel beneath the earth but around the earth and this region, and that it disappears and produces night because the land toward the north is high. Let this, then, and so much, be said by us about why the sea cannot have springs, and for what cause it appears to flow in this way.

6| We must speak about the sea's coming-to-be itself, whether it has in fact come to be, and about its flavor — what the cause is of its saltiness and bitterness. Now the cause that led earlier thinkers to suppose the sea to be a principle and body of all water is this. It would seem reasonable that, just as each of the other elements has an accumulated mass and is a principle because of its abundance — from which, as it is divided off, it changes and mixes with the others, as fire's abundance lies in the upper regions, air's abundance in the region after that of fire, and earth's body is that around which all these plainly lie — so too, by the same reasoning, one must inquire in the same way about water. But no other such body appears to lie gathered together in a mass, as with the other elements, except the bulk of the sea; for the mass of rivers is neither gathered together nor stationary, but always appears to be coming to be anew, day by day. From this very difficulty, then, it was thought that the sea is the principle of the wet things and of all water. Hence some also say that rivers not only flow into it but also out of it; for, they say, as it is filtered, what is salty becomes drinkable.

7| Opposed to this opinion is another difficulty: why, if the sea is a principle of all water, is this collected water not drinkable but salty? The cause will at the same time be the solution of this difficulty, and it is necessary to grasp correctly the first assumption about the sea. For water is extended around the earth, just as the sphere of air is around this, and around that the so-called sphere of fire (for this is outermost of all, whether as most people say or as we say); and since the sun moves in this manner, and since because of this there is change and coming-to-be and passing-away, the finest and sweetest part is drawn up each day and travels, being separated out and turned to vapor, into the region above, and there, being condensed again through cooling, is carried back down again toward the earth. And nature always wishes to do this in this way, as has been said before. Hence all those among the earlier thinkers who supposed that the sun is nourished by moisture are ridiculous. And because of this some indeed say that the sun also makes its turnings on this account; for, they say, the same places cannot always furnish it with nourishment.

8| It is necessary that this happen to it, or else that it perish; for even visible fire lives only so long as it has fuel, and moisture alone is supposed to be fuel for fire — as though the moisture drawn up actually reaches as far as the sun, or as though its ascent were of the same kind as that of a flame coming into being; and taking the plausibility of this as their guide, they supposed the same about the sun. But the two are not alike; for flame comes to be through a continuous succession of moisture and dryness changing into each other, and is not nourished (for it does not remain the same for any length of time, so to speak), whereas this cannot happen in the case of the sun, since if it were nourished in the very way they describe, then clearly the sun would not merely be, as Heraclitus says, "new upon a day," but continuously new at every moment. Further, the drawing-up of moisture by the sun is like that of waters heated by fire; if, then, the fire that is kindled beneath such waters is not itself nourished by them, it would not be reasonable to suppose this of the sun either, not even if by its heating it should vaporize the water entirely. And it is also absurd to be concerned only about the sun, while overlooking the preservation of the other stars, which are so many in both number and magnitude.

9| The same absurdity results also for those who say that, since the earth was originally wet, and the region around the earth was heated by the sun, air came to be and the whole heaven increased in bulk, and that this heaven both supplies winds and produces its own turnings; for we plainly always see the water that has been drawn up coming down again; and even if it is not given back within a year, and not in the same way in every region, still within certain fixed periods it gives back all that was taken up — as if the regions above were not being nourished by it, and as if it were not the case that some of the air, once it has come to be, remains as it is while some of it comes to be and again perishes back into water, but rather as if all of it alike is dissolved and again constituted into water. Now the drinkable and sweet water is all drawn up because of its lightness, while the salty water stays behind because of its weight, not in a place of its own; for this is the point that ought properly to have been raised as a puzzle (it is absurd if there is no place belonging to water, as there is for the other elements) and this is the solution to it: the place we see the sea occupying is not the place of sea but rather of water. It appears to be the place of sea because the salty part stays behind on account of its weight, while the sweet and drinkable part is drawn up on account of its lightness, just as happens in the bodies of animals.

10| For in animals too, when the nourishment that enters is sweet, the residue of the liquid nourishment — the sediment, that is — turns out to be bitter and salty; for the sweet and drinkable part is drawn by the innate heat into the flesh and the rest of the arrangement of the parts, in whatever way each part is naturally suited to take it up. So then, just as in that case, if someone supposed that the belly was not the place of the drinkable nourishment, because it quickly disappears, but was the place of the residue, because he sees this staying behind, he would not be judging rightly — so too in the present case; for this place, as we say, is the place of water. That is why all the rivers, and all the water that comes to be, flow into it; for the flow is toward the lowest-lying place, and the sea occupies just such a place on the earth. But the one part is quickly carried up entirely because of the sun, while the other remains behind for the reason stated. As for pursuing the old puzzle, why such a quantity of water is nowhere apparent (since, although countless rivers flow every day and are immense in size, the sea never becomes any larger) — it is not strange that some have raised this as a puzzle, yet for one who looks into it, it is not hard to see the answer.

11| For the same quantity of water, when spread out over a breadth and when massed together, does not dry up in an equal time, but the difference is so great that the one would remain a whole day, while the other — as if someone were to pour a cup of water spread over a large table — would vanish, one might say, in the time it takes to think of it. This is exactly what happens with rivers too: since they flow continuously and in a mass, whatever arrives is always drying up quickly and imperceptibly once it reaches a vast and broad place. But what is written in the Phaedo about the rivers and the sea is impossible. For it is said that all waters are bored through into one another under the earth, and that the source and spring of all of them is what is called Tartarus, a certain quantity of water around the middle of the earth, out of which all waters, both those that flow and those that do not, are given off; and that the inflow into each of the streams is produced because the first and originating body of water is always surging — for it has no fixed seat, but is always eddying about the middle; and as it moves up and down it produces the outpouring into the streams. And in many places the water forms standing pools, of the sort that our own sea is said to be, but all of it circles round again back to the source from which it began to flow, in many cases at the very same place, but in others at the point directly opposite in position to the outflow — for example, if the rivers began to flow from below, they enter again from above.

12| And the descent, it is said, goes as far as the middle; for beyond that point the motion for all of them is now uphill. And the rivers get their flavors and colors from whatever kind of earth they happen to flow through. But it follows, on this account, that rivers do not always flow to the same place; for since they flow into the middle from the very point from which they flow out, they will be no more likely to flow from below than from above, but toward whichever side Tartarus happens to surge and tilt. And yet if this were so, there would result what is called "rivers flowing upward" — which is impossible. Further, where will the water that comes to be, and the water that is again drawn up, come from? For this whole amount must be extracted from somewhere, if the same total quantity is always to be preserved; for whatever flows out flows back again to the source. And yet all the rivers, as many as do not flow into one another, plainly end in the sea; and none flows into the earth, but even if a river disappears from view, it reappears again elsewhere. The rivers that grow large are those that flow a long distance through a hollow region; for they take in the streams of many rivers, cutting across their courses by way of the terrain and the length of their path. That is why the Danube and the Nile are the greatest of the rivers that empty into this sea of ours.

13| And about the springs, different people give different causes for each of the rivers, because many rivers flow into the same one. Now it is plain that all this is impossible to happen, especially if the sea has its origin from that source. So then, that this place belongs to water and not to sea, and for what cause the drinkable part is not apparent except as it flows, while the other part stays behind, and why the sea is rather an end-point of water than a source of it — just as the residue in bodies is the end-point of all nourishment, and especially of the liquid kind — let this much be said by us.

14| About the saltiness of the sea itself we must speak, and ask whether it is always the same, or whether it neither was nor will be the same but will diminish and give out — for some think this too. Now on this point all seem to agree, that the sea came to be, if indeed the whole universe did; for they make its coming-to-be simultaneous with that of the universe. So it is clear that if the whole is eternal, then this is how one must think about the sea too. As for the view that the quantity of the sea is becoming less, as Democritus says, and will in the end give out entirely, whoever is persuaded of this seems no different from a believer in Aesop's fables. For Aesop too told a myth, that Charybdis, by sucking up water twice, made first the mountains visible, and second the islands, and that by sucking it up a third and last time she will make everything entirely dry. Now for him, angry as he was at the ferryman, it was fitting to tell such a myth, but it is less fitting for those who are seeking the truth; for whatever the cause was that made the sea remain in the first place, whether it was weight, as some of these thinkers too say (for the cause is easy enough to see in this case), or whether it was something else, it is clear that for this same reason the sea must necessarily remain for the rest of time as well. For either they must say that even the water drawn up by the sun will not come back again, or else, if it is going to come back, it is necessary either that the sea always diminishes, or diminishes only until this point is reached, and that the drinkable water must first be drawn up again before that happens.

15| So it will never dry up completely; for that water which had risen earlier will always come back down again before the water it started is exhausted—it makes no difference whether we say this happens once or many times. If someone stops the sun's motion, what will do the drying? But if he lets its circuit continue, then, as we said, the sun will always draw up the fresh water as it approaches, and release it again as it withdraws. People got this idea about the sea from the fact that many regions appear drier now than before; but we have stated the cause of that, namely that this condition results from excesses of rainfall occurring at a given time, not from the coming-to-be of the universe and its parts; and again the opposite will occur, and when it does, the region will dry up again; and this must always proceed in a cycle in this way, for it is more reasonable to suppose this than that the whole heaven changes on this account. But our discussion has lingered over these matters longer than they deserve. As for the sea's saltiness, it is impossible for those who suppose it was generated once and for all, and who generate it as a whole in this way, to account for its being salty. For whether the sea came to be from the residue left behind when all the moisture around the earth was drawn up by the sun, or whether so great a quantity of that flavor was already present in the abundant, sweet water because some such earth had been mixed into it, none the less, once the evaporated water comes back down again, since the quantity is equal, the sea must have been the same at the first as well—

16| —or else, if it was not salty at first, it should not be salty later either. But if it was salty from the very first, one must state the cause, and at the same time explain why, if it was drawn up then too, it does not undergo the same thing now. But indeed, those who make the earth that is mixed in responsible for the saltiness (for they say the earth contains many flavors, so that being carried down together by the rivers, through this mixture it makes the sea salty) face the absurdity that the rivers themselves are not also salty. For how is it possible for the mixture of such earth to become so noticeable in a great quantity of water, but not in each individual river? For it is clear that the sea simply is all the river water together; for it differed from the rivers in nothing except in being salty, and this saltiness comes upon the rivers' water only when they flow together in a mass into the place into which they all run. Equally ridiculous is anyone who, saying that the sea is the earth's sweat, thinks he has said something clear, as Empedocles does; for said this way, for poetry perhaps he has spoken adequately (for metaphor belongs to poetry), but for understanding the nature of the thing it is not adequate; for here too it is not clear how sweat becomes salty out of a sweet drink—whether only something departs, such as the sweetest part, or whether something is mixed in, as in waters that are filtered through ash.

17| The same cause appears to apply also to the residue that collects in the bladder; for that too becomes bitter and salty even though what is drunk and the moisture in one's food are sweet. If, then, just as water filtered through ash becomes bitter, so too in these cases: in the case of urine, some such power is carried down together with it, of the kind that is even seen settling as a salty deposit in vessels; and in the case of sweat, it is separated out together with the moisture from the flesh, as though the moisture leaving the body were washing this element out of it—then it is clear that in the sea as well, what is mixed in together with the moisture from the earth is the cause of the saltiness. Now in the body this kind of thing comes about as the residue of food, on account of incomplete concoction; but in what way it existed in the earth must be stated. And in general, how can it be possible for so great a quantity of water to be secreted out as the earth dries and is heated? For it would have to be only a very small fraction of what is left in the earth. Again, why does the earth not sweat even now, whenever it happens to be drying, whether more or less? For the moisture, that is the sweat, becomes bitter; for if it happened then, it ought to happen now too. But this is not seen to happen; rather, the earth, when dry, becomes moist, and when moist, undergoes nothing of this kind.

18| But how, then, is it possible that at the first coming-to-be, when the earth was moist, it sweated as it dried? Rather it is more likely, as some say, that when most of the moisture had departed and been raised up by the sun, what was left became the sea; and while the earth was moist it was impossible for it to sweat. So the causes of saltiness that are given seem to elude the argument. Let us instead state our own view, taking as our starting point the same one as before. Since it has been established that exhalation is twofold, one moist and one dry, it is clear that this must be supposed to be the principle of such things. And indeed, concerning the question that had to be raised earlier—whether the sea too always persists as the same parts numerically, or whether its parts are always changing in form and in quantity, as with air, fresh water, and fire. For each of these is always becoming something different in succession, while the form of the total quantity of each remains, as with the stream of flowing water and the stream of flame. This much is clear and plausible—that the same account cannot fail to hold for all these cases, and that they differ only in the speed or slowness of change in each case, and that there is both destruction and coming-to-be, but that this happens to all of them in an orderly way.

19| Given that this is so, we must try to render the cause with respect to saltiness as well. It is clear from many signs that this flavor comes about through some admixture. For in bodies, what is least concocted is salty and bitter, as we said before; for the residue of moist nourishment is the least concocted; and this holds of all sediment, but most of all of that which collects in the bladder. A sign of this is that it is the thinnest; for everything that is concocted is naturally disposed to solidify. Then again, there is sweat, in the cases where the same substance is separated out together with it, which is what produces this flavor. The same holds, too, in things that are burned: wherever the heat fails to master the material, in bodies a residue results, and in things being burned, ash results. This is why some say the sea came to be from earth that had been burned up. To put it that way is absurd, but that it comes from that sort of earth is true; for just as in the cases mentioned, so too in the universe as a whole, we must always think in terms of things that grow and come to be according to nature—that what is left over from things that have been fired is earth of this kind, and in particular that this applies to all the exhalation that occurs in the dry state; for it is this exhalation that supplies this great quantity.

20| Since, as we have said, the vaporous exhalation and the dry exhalation are mixed together, whenever they combine to form clouds and water, some quantity of this power must always be enclosed within them, and must be carried down again together with the water in rains, and this must always happen according to a certain order, insofar as things in this region admit of sharing in order at all. We have now stated the source from which the generation of the saltiness present in water comes. And this is also why southerly rains fall in broader drops, as do the first rains of autumn; for the south wind is the warmest of winds both in its size and in its current, and it blows from dry, hot regions, so that it carries little vapor with it. This is why it is warm; for even if it is not warm in itself, but starts out cold from the place where it begins to blow, none the less, as it proceeds, because it takes up along with it much dry exhalation from the neighboring regions, it becomes warm. The north wind, on the other hand, being vaporous, since it comes from moist regions, is for this reason cold; but because it pushes clouds away, the sky here is clear when it blows, while in the opposite regions it is rainy. Similarly, the south wind is clear-skied for the peoples around Libya. So a large amount of such matter contributes to the water that comes down, and this is why the rains of autumn fall in broad drops; for the heaviest parts must be carried down first.

21| So in whatever contains a quantity of this kind of earthy stuff, that stuff sinks to the bottom fastest of all. And the sea is warm for this same reason: everything that has been fired has heat in it potentially. One can also see this in the case of lye, and ash, and the sediment of animals, both the dry sediment and the wet; and it turns out that the sediment of the animals that are hottest in the belly is the hottest sediment of all. So the sea is always becoming more spread out on account of this cause, and some part of it is always being drawn up together with the sweet water; but it is drawn up in a smaller amount, by just as much as, in the rain that falls, the salty and earthy element is less than the sweet. That is why the sea remains, roughly speaking, at an equal level throughout. And that what rises as vapor becomes drinkable, and that the vaporizing part is not combined again into sea water when it condenses back, we state from experience. The same thing happens with other liquids too: for wine and all the flavored liquids, whichever of them vaporize and then condense again into liquid, become water; for the other properties belong to water because of some admixture, and whatever the thing mixed in is, that is the kind of flavor it produces. But an inquiry into these matters must be carried out on other, more suitable occasions. For now let us say just this much: that since the sea exists, something is always being drawn up from it and becomes drinkable, and from above, in the rain, something else comes down that has come into being, not the very water that was drawn up.

22| And it is because of its weight that it settles beneath the drinkable water. And because of this the sea neither runs short, as rivers do, except in particular places (and this must happen in the same way in both cases), nor do the same parts of it persist forever, whether of the earth or of the sea — only the total bulk remains the same. For one must suppose the same about the earth too: part of it rises up, part sinks down again, and the parts that lie on the surface and the parts that go down exchange places with each other. That the salty element is present as a mixture of something is clear not only from what has been said, but also if one shapes a vessel of wax and sets it in the sea, tying its mouth round with something so that the sea cannot pour in: for the water that comes in through the waxen walls becomes drinkable water; for just as through a strainer, the earthy element is filtered out, along with what produces the saltness through admixture. This same thing is also the cause of the weight of sea water (for salt water draws down more than fresh water) and of its thickness; and indeed the thickness differs so much that ships carrying the same weight of cargo sink almost to the point of going under in rivers, but ride at a moderate depth and sail well in the sea — which is why some of those loading ships in rivers have suffered losses through this very ignorance.

23| A proof that the bulk of what is mixed in is rather thick is this: if one makes water very salty by mixing in salt, eggs float on it even when full; for it becomes almost like mud — so great is the bodily bulk the sea contains. People do this same thing also in salting fish for preserving. And if there really is, as some tell in myth, such a lake in Palestine that if one binds a man or a beast of burden and throws them in, they float and do not sink beneath the water, this would be testimony to what has been said; for they say the lake is so bitter and salty that no fish can live in it, and that clothes, if soaked and shaken about in it, come clean. Signs of this sort are all signs of what has been said, namely that the salty element makes a certain body, and that what is present in it is earthy. For in Chaonia there is a spring of rather thick water, which flows off into a nearby river that is sweet but has no fish in it; for the people there, as they tell in their local myth, chose, when the power was granted them by Heracles when he came driving the cattle from Erytheia, to have salt instead of fish, which are produced for them from the spring: for they boil down a portion of this water and set it aside, and when the moisture evaporates off together with the heat, and the water cools, it becomes salt — not in lumps, but loose and fine, like snow.

24| These salts are weaker in strength than other salts, and more of them must be thrown in to sweeten a dish, and they are not as white in color. Something similar to this also happens among the Umbrians: there is a certain place there where reed and rush grow naturally; they burn these, and throw the ash into water and boil it down; and when they have left only a little of the water, this, once cooled, becomes a quantity of salt. As for the salty streams of rivers or springs, one must suppose that most of them were once hot, and that afterward the source of the fire was extinguished, while the earth through which they are filtered still remains, as it were, lye and ash. And in many places there are also springs and river-streams that have flavors of every kind, the cause of all of which must be assigned to the power of fire present in them, or coming to be in them: for earth that is burned, more or less, takes on shapes and colors of flavor of every kind; for it becomes full of the powers of alum and lye and other such things, through which the waters that are filtered, though sweet to begin with, are changed — some becoming sour, as in the Sicanian region of Sicily; for there a sour brine occurs, and people use it like vinegar for some of their foods. There is also, around Lyncus, a spring of sour water, and around Scythia one that is bitter;

25| and what flows off from it makes the whole river into which it empties bitter. The differences among these are plain from what has been said. What flavors arise from what blendings has been discussed separately elsewhere. Concerning waters and the sea, then — the causes on account of which they exist continuously forever, and how they change, and what their nature is, and further how many properties naturally happen to them, whether as things they do or things done to them — we have now said nearly everything about most of these matters.

26| Let us speak now about winds, taking as our starting point what we have already stated earlier. For there are two forms of exhalation, as we say, the one moist, the other dry. The one is called vapor; the other, taken as a whole, has no name, but since we must use the term for a part of it to name the whole, we call it, generally, smoke. Now neither the moist exists without the dry, nor the dry without the moist, but all these things are named according to which predominates. As the sun moves in its circle, then, whenever it draws near it draws up the moisture by its heat, and when it moves farther off, through the resulting cooling, the vapor that had been drawn up condenses again into water; that is why rain occurs more in winter, and at night rather than during the day — though it does not seem so, because what happens at night escapes notice more than what happens during the day. Now all the water that comes down is distributed into the earth; and there is much fire and much heat present in the earth, and the sun not only draws up the moisture that lies on the earth's surface but also, by heating the earth itself, dries it out. Since the exhalation, as has been said, is of two kinds, the vapor-like and the smoke-like, both kinds must necessarily occur.

27| Of these two, the exhalation that has the greater share of moisture is the principle of the water that falls as rain, as has been said before, while the dry exhalation is the principle and nature of winds generally. That this is necessarily how things turn out is clear also from the facts themselves: for the exhalation must be of different kinds, and it is not merely possible but necessary that the sun and the heat in the earth produce these two kinds. And since the form of each is distinct, it is evident that they differ, and that the nature of wind is not the same as the nature of the water that falls as rain, as some people say — that the very same air, when it is in motion, is wind, and when it condenses again, is water. Now air, as we have said in the discussions before this one, comes to be out of these two exhalations: for vapor is moist and cold (moist because it is easily bounded, cold because, being of water, it is cold by its own nature, like water that has not been heated), while smoke is hot and dry. So that, as if compounded out of a combination of the two, air would be constituted moist and hot. And indeed it would be absurd if the air that lies spread around each of us should become wind simply by being set in motion, and should be wind wherever it happens to be moved from — and not rather (just as we suppose that rivers are not water flowing in any random way, however great its quantity, but must be water flowing from a spring) that the case is the same also with winds:

28| for a great quantity of air might be set in motion by some great collapse, and yet have no principle or spring. What actually happens bears out what has been said: because the exhalation is continuous, but comes to be in greater or lesser amount at different times, clouds and winds are always produced, in each season, in the way that is natural to it; and because sometimes the vapor-like exhalation becomes many times greater, and at other times the dry, smoke-like exhalation does, at some times the years turn out rainy and wet, at other times windy, and there are droughts. Now sometimes it happens that both droughts and heavy rains occur widely and over a continuous region at once, and sometimes only in parts; for often the region all around receives the seasonable rains, or even more, while in some part of it there is drought; and sometimes, on the contrary, while the whole surrounding region has moderate rainfall, or is even rather dry, one particular portion receives an abundant quantity of water. The cause is that, for the most part, it is likely that the same condition extends over a fairly large region, because places close to one another lie in much the same relation to the sun, unless they happen to have some peculiar difference of their own;

29| yet sometimes in one part the dry exhalation came to be the greater, and in another the vapor-like exhalation did, and sometimes the reverse. And the cause of this itself is that each kind changes over into the exhalation belonging to the neighboring region — for instance, the dry exhalation flows off toward its own proper region, while the moist flows toward the region next to it, or is even pushed off by winds to some far-off place; and sometimes this exhalation stays put, while the opposite one does the same thing. And this often happens just as in the body: if the upper cavity is dry, the lower is disposed in the opposite way, and when this is dry, the upper is moist and cold — so also with regions, the exhalations shift about and change places with one another. Further, after rains, wind generally arises in those very places where the rains happened to occur, and the winds cease once the water has come to be. For these things necessarily happen because of the causes stated: for when it has rained, the earth, being dried both by the heat within it and by the heat from above, gives off an exhalation, and this was the body of wind. And whenever there is this sort of separating-off and winds hold sway, then, as they cease because the hot is continually being separated off and carried up into the region above, the vapor condenses as it cools and becomes water;

30| and when the clouds are pushed together into one place and the cold turns back into them all around, water is produced and it cools the dry exhalation. So the coming to be of rain stops the winds, and when the rains stop, wind comes to be again for these same reasons. Further, the same cause explains why winds arise most of all from the region of the north and of the south: for the north and south winds are the most numerous of all winds; for the sun alone does not travel over these regions, but moves toward them and away from them, while it always travels toward the west and toward the east. Hence the clouds gather at the sides, and as the sun approaches, the exhalation of moisture occurs, and as it departs toward the opposite region, water and storms occur. So it is because of this movement toward the solstices and away from the solstices that summer and winter come about, and the water is carried up and comes to be again. And since the greatest amount of water comes down in those regions toward which and from which the sun turns — and these are the region toward the north and toward the south — and since where the earth receives the most water, there the exhalation must necessarily be greatest, much as smoke rises from green wood, and this exhalation is wind, it stands to reason that the most numerous and most dominant of the winds should arise from there.

31| Those that come from the north are called north winds, and those from the south, south winds. Their movement is oblique: for although the exhalation rises straight up, they blow around the earth, because all the air in a circle follows along with the movement. Hence one might also raise the question, from which direction the principle of winds comes, whether from above or from below: for the motion is from above even before the wind blows, while the air makes this evident, even if there is cloud or mist present; for it shows a moving principle of wind before the wind has plainly arrived, as though the winds had their principle from above. But since wind is a certain quantity of the dry exhalation from the earth, moving about the earth, it is clear that the principle of its motion is from above, while the principle of its matter and its coming to be is from below: for insofar as the rising exhalation will flow, the cause of that comes from above, since the movement of the more distant regions governs that of the earth; and at the same time, while it rises straight up from below, and everything is stronger the nearer it is, the principle of its coming to be is plainly from the earth. That it comes from many exhalations gradually coming together, just as the sources of rivers arise as the earth becomes moist, is clear also from what actually happens:

32| for at the very place from which winds blow on each occasion, they are all weakest, while as they advance and get further off, they blow strong and clear. Further, the regions around the north are, in winter, calm and windless in that very place; but the small amount that blows off unnoticed, once it has advanced outward, becomes a strong wind. What, then, is the nature of wind and how it comes to be, and further, concerning droughts and heavy rains, and for what cause they both cease and arise after rains, and why north and south winds are the most numerous of winds, has been stated; and, in addition to this, also concerning their movement.

33| The sun both stops winds and starts them up together with itself. For when the exhalations are weak and few, it withers, by its greater heat, the lesser heat that is in the exhalation, and disperses it. Further, it dries the earth itself before any massed discharge can occur, just as, when a little fuel falls into a great fire, it is often consumed before it can even make smoke. For these reasons, then, the sun both stops winds and prevents them from arising in the first place — stopping them by withering, and preventing their arising by the speed of the drying. This is why calm weather occurs especially around the rising of Orion, and continues up to the etesian winds and their forerunners. In general, calms occur through two causes: either because the exhalation is quenched by cold, as happens when a strong frost sets in, or because it is withered away by stifling heat. But most calms occur in the intervening seasons, either because the exhalation has not yet begun, or because the earlier exhalation has already passed off and another has not yet begun to flow in. Orion is thought to be a hard and stormy sign, both setting and rising, because its setting and its rising occur at a change of season, in summer or in winter, and because, on account of the size of the constellation, a certain number of days is taken up in its rising and setting;

34| and changes of every kind are turbulent, on account of their indeterminacy. The etesian winds blow after the solstice and the rising of the dog star, and neither at the time when the sun is closest, nor when it is farthest off; and they blow by day, but stop at night. The cause is that when the sun is near, it dries things up before the exhalation can arise; but when it has withdrawn a little, the exhalation and the heat now become commensurate, so that the frozen waters melt, and the earth, being dried both by its own heat and by that of the sun, is as it were made to smoke and steam. At night they slacken, because the melting of the frozen matter stops on account of the coldness of the nights. Nothing steams that is either frozen or has no moisture in it at all — only when what is dry has moisture does this, being heated, give off steam. Some raise the difficulty of why continuous north winds occur, which we call etesian winds, after the summer solstice, while south winds do not occur in this way after the winter solstice. And the fact is not without reason. For the so-called white-south-winds do occur in the opposite season, but they do not occur continuously in the same way, and so, passing unnoticed, they lead people to raise the question. The cause is that the north wind blows from the regions beneath the Bear, which are full of much water and snow; and as these are melted by the sun, the etesian winds blow more after the summer solstice than at the solstice itself;

35| for in just this way the stifling heat also occurs, not when the sun is closest to the Bear, but when it has been heating for a longer time, while still being near. Similarly, after the winter solstice the bird-winds blow; for these too are weak etesian winds. They are fewer and blow later than the etesian winds proper — they begin to blow on the seventieth day, because the sun, being far off, has less strength. They do not blow as continuously, because at first it is the things on the surface, weak ones, that are given off, whereas the more solidly frozen matter needs more heat. This is why these winds blow with gaps, until the etesian winds blow again at the next summer solstice, since a wind, once it begins from a given source, wants above all to blow from there continuously. The south wind blows from the summer turning-point, and not from the other Bear. For there being two divisions of the region capable of being inhabited — one toward the pole above us, the other toward the other pole and toward the south — and the earth being shaped, as it were, like a tambourine (for such is the shape that the lines drawn from its center cut out), they make two cones, one having the tropic circle as its base, the other the circle that is always visible, with the apex at the middle of the earth;

36| and in the same way, toward the lower pole, two other cones cut out other segments of the earth. Only these regions are capable of being inhabited, and not the regions beyond the tropics either; for there would be no shadow toward the north — but as it is, those places become uninhabitable through heat before the shadow either disappears or shifts toward the south; while the regions under the Bear are uninhabitable through cold. The Crown, too, moves in this same region; for it appears passing directly overhead for us, when it is on the meridian. This is why people draw maps of the circuits of the earth ridiculously nowadays; for they draw the inhabited world as circular, and this is impossible both according to the observed facts and according to reasoning. For reasoning shows that it is bounded in breadth, while it is possible for it to join up in a circle because of the blending of climate — for the heat and the cold do not exceed the bounds of habitability in length, but in breadth, so that, unless some expanse of sea prevents it, the whole would be passable — and the observed facts about voyages and journeys show the same, for the length differs greatly from the breadth. For the distance from the Pillars of Heracles to India is, compared with that from Ethiopia to Lake Maeotis and the outermost regions of Scythia, more than five to three in magnitude, if one reckons the voyages and the roads, so far as it is possible to obtain accuracy in such matters.

37| And yet in breadth we know the inhabited world only as far as the uninhabited regions — for in one direction people no longer dwell because of the cold, in the other because of the heat. The regions beyond India and beyond the Pillars of Heracles do not appear, because of the sea, to link up so as to make the whole inhabited world continuous. Since it is necessary that some region toward the other pole stand in the same relation to it as the region we inhabit stands to the pole above us, it is clear that the arrangement of the winds too, along with other things, will hold analogously; so that just as here there is a north wind, so for those people too there will be some wind of that kind blowing from the Bear that is there, none of which can possibly reach here — since not even this north wind of ours reaches the whole inhabited world here. For the north wind is, as it were, a local land-wind, extending only so far as this north wind blows into the inhabited world here. But because our habitation lies toward the north, north winds blow most frequently. All the same, even here it falls short and cannot extend far, since around the southern sea beyond Libya, just as here north and south winds blow, so there east and west winds blow continuously in succession one after another. It is clear, then, that the wind blowing from the other pole is not the south wind.

38| Since it is neither that wind nor the one from the winter turning-point — for then there would have to be another wind from the summer turning-point as well, since that is what the analogy would require. But as things are, there is not; for only one wind appears to blow from those regions there. So it is necessary that the wind blowing from the burnt-up region be the south wind. That region, because of its nearness to the sun, has no waters and pasture-lands that, by freezing, would produce etesian winds. But because that region is much larger and open, the south wind is greater and more frequent and warmer than the north wind, and reaches here more than this one reaches there. We have now stated, then, what is the cause of these winds, and how they stand in relation to one another.

39| Now let us speak about the position of the winds — which are opposite to which, which can blow together and which cannot, further how many and what winds there actually happen to be, and besides these about the other conditions not covered in the particular problems already discussed. The account of their position must be studied together with the diagram. It has been drawn, for the sake of clearer presentation, as the circle of the horizon — that is why it is round. One must think of its other segment as the one inhabited by us; for that too can be divided in the same way. Let it first be assumed that things opposite in place are those most distant from one another in place, just as things opposite in form are those most distant in form. Things are most distant in place when they lie against one another along a diameter. Let the point A, then, be the equinoctial west; and let the place opposite to it, B, be the equinoctial east. Let another diameter cut this one at right angles, its point H being the north; opposite to this, directly across, is Th, the south. Let Z be the summer sunrise, E the summer sunset, D the winter sunrise, and G the winter sunset.

40| From Z let a diameter be drawn to G, and from D to E. Since, then, things most distant from one another in place are opposite in place, and things lying along a diameter are most distant, it follows of necessity that those winds too are opposite to one another which lie along a diameter. According to the position of their places the winds are named as follows: Zephyr is the wind from A, for this is the equinoctial west. Opposite to it is Apeliotes from B, for this is the equinoctial east. Boreas, that is Aparctias, is from H, for the north is there. Opposite to this is Notos from Th; for this is the south, from which it blows, and Th is opposite H, since they lie along a diameter. From Z comes Caecias; for this is the summer sunrise. Opposite to it is not the wind blowing from E, but Lips from G; for this blows from the winter sunset, and it is opposite Caecias, since it lies along the diameter. The wind from D is Eurus; for this blows from the winter sunrise, bordering on Notos, which is why they are often said to blow together as Euronotus. Opposite to this is not Lips from G, but the wind from E, which some call Argestes, others Olympias, and others Sciron;

41| for this blows from the summer sunset, and it alone lies opposite Eurus along the diameter. These, then, are the winds positioned along a diameter, together with the winds each is opposite to; but there are others for which there are no opposite winds. From I comes the one they call Thrascias; for this lies between Argestes and Aparctias. From K comes the one they call Meses; for this lies between Caecias and Aparctias. The diameter I-K tends to coincide with the one running through the whole figure, but not exactly. There is no wind opposite to these, neither to Thrascias nor to Meses — for a wind would then have to blow from the point M, since this lies along the diameter — nor to the wind from I, Thrascias; for a wind would then have to blow from N, since this is the point along the diameter — unless indeed some slight wind does blow from that very point, which the people of that region call Phoenicias. These, then, are the principal and clearly distinguished winds, and they are arranged in this manner. The reason there are more winds from the northern regions than from the southern is, first, that our inhabited world lies toward that region, and second, that far more water and snow are driven away into this part, because those other regions lie under the sun and in its path; and since this water and snow, once melted into the earth, are warmed both by the sun and by the earth, the exhalation produced must necessarily be greater and cover a wider region, for this reason.

42| Of the winds named, Boreas is most properly Aparctias, while Thrascias is shared between Argestes and Meses; Caecias is shared between Apeliotes and Boreas; Notos is both the native wind from the south and Lips; Apeliotes is both the wind from the equinoctial east and Eurus; Phoenicias is a shared wind; and Zephyr is both the native wind and the one called Argestes. In general some of these are called northerly, others southerly. The zephyr-type winds are reckoned with Boreas, since they are colder for blowing from the west, while the apeliotes-type winds are reckoned with Notos, since they are warmer for blowing from the east. Since the winds are distinguished by cold, heat, and mildness, they were named in this way accordingly. Winds from the dawn are warmer than those from the sunset, because the winds from the east lie under the sun for a longer time, while those from the west leave it sooner and approach that region later. Since the winds are arranged in this way, it is clear that opposite winds cannot blow at the same time — for they lie along a diameter, so that one of the two will be overpowered and cease — but nothing prevents winds not positioned this way in relation to one another from blowing together, as with Z and D.

43| This is why both sometimes blow favorably at once toward the same point, though not from the same place nor as the same wind. It is in the opposite seasons that opposite winds blow most, for example around the spring equinox Caecias, and in general the winds beyond the summer solstice, while around the autumn equinox it is the Lips-winds; around the summer solstice it is Zephyr, and around the winter solstice Eurus. Aparctias, Thrascias, and Argestes fall upon the other winds most of all and stop them; for because their starting-point is nearest, these blow most often and most strongly. This is also why they are the clearest-weather winds of all; for blowing from nearby, they overpower and stop the other winds, and by blowing apart the clouds that gather they produce clear weather — unless they happen at the same time to be extremely cold. In that case they are not clear-weather winds; for if they are more cold than strong, they freeze the clouds before they can drive them on, or else push them forward instead. Caecias is not a clear-weather wind, because it curves back upon itself; hence the proverb, drawing to himself, as Caecias does a cloud. Their shifts occur as they die down into the winds next to them, following the movement of the sun, since the wind next to the starting-point is the one most set in motion. And the starting-point of the winds moves in this way, just as the sun does.

44| Opposite winds produce either the same effect or the opposite one — for instance Lips and Caecias, which some call Hellespontias, are both moist, as is Eurus, which some call Apeliotes. Argestes and Eurus are dry; Eurus is dry at the start but becomes rainy toward the end. Meses and Aparctias are especially snow-bringing, for these are the coldest. Aparctias, Thrascias, and Argestes are hail-bringing. Notos, Zephyr, and Eurus are scorching. With clouds Caecias thickens the sky very much, Lips with sparser ones; Caecias does so both because it curves back upon itself and because it is shared between Boreas and Eurus, so that, being cold, it freezes and condenses the vaporous air, while, being easterly by its region, it carries abundant material and vapor, which it drives forward. Aparctias, Thrascias, and Argestes are clear-weather winds; the reason has been stated earlier. These, together with Meses, are especially given to lightning; for because they blow from nearby they are cold, and lightning arises from cold, being separated out as the clouds come together. This is also why some of these same winds are hail-bringing, for they freeze quickly. Storm-winds occur mostly in autumn, then in spring, and especially Aparctias, Thrascias, and Argestes.

45| The cause of this is that whirlwinds occur most of all when, as some winds are blowing out, others fall in upon them, and these fall in upon the others most of all when the others are blowing; the cause of this too has been stated earlier. The etesian winds shift, for those who live in the west, from the north wind round to the northwest, the northwest-by-west, and the west winds (for the north wind is a west wind), beginning from the north and ending at the winds farthest from it; for those who live toward the east they shift round as far as the east wind. Concerning the winds, then, their origin and substance from the start, and the affections that occur in common and around each one individually, let so much have been said by us.

46| After this we must speak about earthquake and the motion of the earth; for the cause of this affection belongs to the same class as the one just discussed. The views handed down up to the present time are three, and from three men. Anaxagoras of Clazomenae, and before him Anaximenes of Miletus, declared themselves on it, and later than these, Democritus of Abdera. Anaxagoras, then, says that the aether, being naturally borne upward, falls in beneath the earth and into its hollow places and moves it; for the upper parts, he says, have become compacted together because of the rains, since by nature the whole is equally porous, there being an upper and a lower part of the whole sphere, and the part we happen to inhabit being the upper one, the other the lower. Now against this cause perhaps nothing need be said, as it is stated too simply; for to suppose that up and down are such that the bodies possessing weight are not borne toward the earth from every direction, but the light bodies and fire move upward, is naive, especially when we see that the horizon of the inhabited world, so much of it as we know, is constantly becoming different as we shift our position, which shows that the earth is convex and spherical;

47| and also to say that it rests upon the air because of its size, and then to assert that it is shaken by being struck from below upward over its whole extent. Besides this, he accounts for none of the things that happen in connection with earthquakes; for it is not any chance regions or seasons that share in this affection. Democritus says that the earth, being full of water, and receiving in addition much rain water, is moved by this; for when the water becomes too much for the hollow places to receive, it forces its way through and produces the earthquake by its violence, and again when the earth is drying out and drawing the moisture that is changing from the fuller places into the empty ones, its falling in causes motion. Anaximenes says that the earth, being wetted and dried, breaks apart, and is shaken by the falling in of the hills that break off in this way; that is why earthquakes occur both in droughts and again in excessive rains; for in droughts, as has been said, the earth dries out and breaks apart, and it is broken through by being oversaturated with waters. But if this were what happens, the earth ought to be seen sinking down in many places as a result. Further, for what cause does this affection occur often around certain regions that differ in no such degree from the others? Yet it ought to. And in general, for those who suppose things in this way, it is necessary always to say that earthquakes occur less, and that in the end the earth's shaking will stop at some point;

48| for what is being packed together has this kind of nature. So if this is impossible, it is clear that this cause too is impossible. But since it is evident that exhalation must arise both from what is moist and from what is dry, as we said earlier, it is necessary, given that these exist, that earthquakes occur. For the earth is in itself dry, but because of the rains it has within itself much moisture, so that, being heated both by the sun and by the fire within it, much wind comes to be outside it and much inside it; and this sometimes flows all continuously outward, sometimes all inward, and sometimes it is even divided. If, then, this cannot be otherwise, the next thing to consider would be which of the bodies would be most capable of causing motion; for it is necessary that what is naturally disposed to travel the greatest distance and be most violent should be of this sort. Now the swiftest-moving is necessarily the most violent, for it strikes hardest because of its speed; and what is most capable of passing through everything travels the greatest distance, and this is the finest-textured. So if the nature of wind is of this sort, wind is the most capable of motion among bodies; indeed fire too, when combined with wind, becomes flame and is carried swiftly. Neither water nor earth, then, could be the cause, but wind is the cause of the motion, whenever the exhalation that is being given off outward happens to flow inward instead.

49| That is why most and the greatest earthquakes occur in calm weather; for the exhalation, being continuous, follows for the most part the impulse of its starting point, so that it rushes either all inward at once or all outward. That some occur even when wind is blowing is not at all unreasonable; for we sometimes see several winds blowing at once, and whenever one of these rushes into the earth, the earthquake will occur even though wind is blowing. These are lesser in magnitude because their starting point and cause are divided. And most and the greater earthquakes occur by night, while those of the day occur around midday; for midday is for the most part the calmest time of day (for when the sun has the greatest power, it shuts the exhalation up inside the earth; and it has the greatest power around midday), and the nights are calmer than the days because of the absence of the sun; so that the flow becomes inward again, like an ebb tide, in the opposite direction from the outward flood, and this happens especially toward dawn; for that is when winds too naturally begin to blow. If, then, their starting point happens to change to an inward flow like the Euripus, it makes the earthquake stronger because of the quantity involved.

50| Further, the strongest earthquakes occur around such regions as these, where the sea is subject to currents or the land is porous and full of caverns. That is why they occur around the Hellespont and around Achaea and Sicily, and around those regions of Euboea; for the sea seems to run through channels under the earth there. That is also why the hot springs around Aedepsus have arisen from a cause of this kind. Around the regions mentioned, earthquakes occur most of all because of the narrowness; for the wind, becoming violent because of the quantity of sea being carried against it in large amount, is thrust back again into the earth, at least that part of it which is naturally disposed to blow off from the earth. And those regions that have porous ground beneath them, receiving much wind, are shaken more. And earthquakes occur most in spring and autumn, and in excessive rains and in droughts, for the same cause; for these are the windiest seasons, since summer and winter, the one because of the frost, the other because of the heat, produce a lack of motion; for the one is excessively cold, the other excessively dry. And in droughts the air is windy; for this is exactly what drought is, when the dry exhalation becomes greater than the moist one;

51| while in excessive rains it makes the internal exhalation greater, and, this discharge being cut off within narrower regions and forced into a smaller space, when the hollow places become filled with water, and this begins to prevail because a large quantity is compressed into a small space, the wind, flowing and striking against the earth, moves it violently. For we must understand that, just as in our own body the confined force of wind is the cause both of tremors and of pulsations, so too in the earth wind produces similar effects, and one kind of earthquake is like a tremor, another like a pulsation, and just as it often happens after urination throughout the body (for there occurs a kind of trembling as the wind changes place all at once from outside to inside), such things occur in connection with the earth as well. And how great a power wind has must be observed not only from what happens in the air (for there, because of its size, one might suppose it capable of producing such effects) but also in the bodies of living creatures; for tetanus and convulsions are motions of wind, and they have such strength that many people trying together to overpower them are unable to master the motion of those who are ill.

52| We must think that the same thing happens in the earth too, if we imagine it on a smaller scale relative to a larger one. And signs of this have appeared in many places, within reach of our own perception. For before now, an earthquake occurring in certain places did not stop until the wind that had caused the motion broke out clearly, like a whirlwind, into the region above the earth—as happened recently near Heraclea on the Pontus, and earlier near the Holy Isle, which is one of the islands called the Islands of Aeolus. For on that island part of the earth swelled up, and a mound-like mass rose with a noise; finally, when it burst, a great blast of wind came out, and it threw up cinder and ash, and it covered with ash the whole city of the Liparaeans, which is not far off, and it reached some of the cities in Italy; and even now the place where this eruption occurred is plain to see. Indeed we must suppose this to be the cause of the fire that occurs in the earth as well: it happens when the air, having been broken up into small parts and struck together, first bursts into flame. A proof that winds flow beneath the earth is also found in what happens around these islands: when a south wind is about to blow, it gives a sign of it beforehand—

53| for the places from which the eruptions occur echo, because the sea is already being pushed forward from far off, and the exhalation coming up out of the earth is pushed back inward again by it, wherever the sea is advancing. And it makes a noise without an earthquake, both because of the openness of the places (for the exhalation pours out into what is unbounded outside) and because of the small quantity of air being pushed back. Further, the sun's becoming hazy and dimmer without any cloud, and, before dawn earthquakes, a windlessness and a strong cold that sometimes occur, are signs of the cause we have stated. For the sun must become hazy and dim as the wind—which dissolves and separates the air—begins to retreat into the earth, and toward dawn and around daybreak there must be windlessness and cold. For the windlessness must, as a rule, occur, just as has been said before, since the wind is, so to speak, flowing back inward, and this is truer the more so before the greater earthquakes; for since it is not torn apart, part going out and part staying in, but is carried along as a mass, it must be stronger. And the cold occurs because the exhalation—which is naturally hot in its own right—is turned back inward.

54| Winds do not seem to be hot, because they set in motion air that is full of cold and abundant vapor, just like the breath blown out through the mouth. For this breath too is hot close up, as also when we pant, but because there is so little of it, this is not equally noticeable, while from a distance it is cold, for the same reason as with the winds. So when this kind of power fails to reach the earth, the vaporous outflow, condensing because of its moisture, produces the cold, in whichever places this condition happens to occur. And the same cause also explains the sign that sometimes customarily occurs before earthquakes: either during the day or a little after sunset, in clear weather, a thin cloud appears, stretched out and long, like the length of a line drawn with exact straightness, as the wind withers away because of its shift of direction. And the same thing happens at sea, around the shores: when the sea, being rough, casts up waves, the breakers become very thick and crooked, but when there is calm, because the discharge it makes is small, they run thin and straight. So what the sea does around the land, the wind does around the haze in the air, so that when windlessness sets in, the cloud is left altogether straight and thin, like a breaker made of air.

55| Because of these same causes, it also happens sometimes that an earthquake occurs around eclipses of the moon. For when the obstruction is already near, and the light and the heat from the sun have not yet altogether left the air, but are already withering away, windlessness occurs as the wind shifts back into the earth, and this produces the earthquake before the eclipses. For winds also frequently arise before eclipses—winds at dusk before midnight eclipses, and winds at midnight before dawn eclipses. This happens because the heat from the moon grows dim, when its motion is already near the point at which, once it has reached it, the eclipse will occur. So when the air, which was being held down and kept at rest by this heat, is released, it is set in motion again, and a wind arises earlier than the eclipse. And when an earthquake becomes violent, it does not stop shaking at once, nor all in a single stroke, but at first it often continues for as much as forty days, and later it gives off after-tremors in the same places for one year and even two. The cause of the magnitude is the quantity of the wind and the shapes of the places through which it happens to flow; for wherever it meets resistance and does not pass through easily, there it shakes most, and it is bound to be left trapped in the difficult passages, like water that cannot get through.

56| This is why, just as in the body the pulses do not stop suddenly or quickly, but the affection dies away gradually, by degrees, so too the source from which the exhalation arose and the onrush of the wind clearly does not use up all at once the whole matter out of which it produced the wind we call an earthquake. So as long as what remains of this matter is not used up, the earth must go on shaking, but more gently, and this continues until what is being exhaled becomes too little to be able to cause perceptible motion. The wind also produces the noises that occur under the earth, both those before earthquakes and those that have before now occurred underground even without earthquakes. For just as air struck gives off noises of every kind, so also does air itself striking—it makes no difference, for whatever strikes is at the same time itself struck, in every case. And the noise runs ahead of the motion, because it consists of finer parts and the noise of the wind travels more easily through everything. And when the wind is too weak, because of its fineness, to move the earth, then because it easily filters through it cannot cause motion, but because it strikes solid masses and hollow ones and shapes of every kind, it gives off sounds of every kind, so that sometimes it seems—just as the tellers of marvels say—that the earth is bellowing.

57| Before now, waters have also burst forth when earthquakes occurred; but the water is not for this reason the cause of the motion, but whether the wind forces its way from the surface or from below, that is what is doing the moving—just as with waves, the winds are the cause, not the waves the cause of the winds—since on this reasoning one might just as well blame the earth itself for the affection; for it is overturned when it is shaken, just as water is (for a spilling-out is a kind of overturning). But both of these are causes only as matter (for they are acted upon, but do not act), while the wind is a cause as a principle. Wherever a wave has occurred together with an earthquake, the cause is that the winds are running counter to each other. This happens whenever the wind that is shaking the earth, being driven along by another wind, is not able to push the sea away entirely, but by pushing it forward and compressing it gathers a great mass of it into one place; for then, this wind being overpowered, the mass of sea that is being pushed by the opposing wind must burst out all at once and produce the flood. This also happened around Achaea: for outside there was a south wind, but there, a north wind, and when windlessness set in and the wind flowed inward, the wave and the earthquake occurred together, and all the more because the sea did not allow a vent for the wind that had set out beneath the earth, but blocked it instead—

58| For as they force each other apart, the wind produced the earthquake, and the settling of the wave produced the flood. Earthquakes of the earth occur locally, and often over a small area, but winds do not occur locally. They occur locally whenever the exhalations in that place and in the neighboring one come together into one, just as we said droughts also come about, and local excessive rains. Earthquakes, then, come about in this way, but winds do not: for earthquakes have their starting point in the earth, so that they all rush toward one point; but the sun cannot do this in the same way, but rather has more power over the exhalations that are up in the air, so that they flow, whenever they take their starting point from the sun's motion, toward one point according to the differences of the places. So then, whenever the wind is great, it moves the earth broadly, as a trembling would, but this happens rarely and only in certain places; when it moves up and from below, as a pulse does, and for this reason the earth shakes less often in this way; for it is not easy for so much of a source to come together in this fashion, since the separation lengthwise is many times greater than that from the depth.

59| Wherever such an earthquake occurs, a great number of stones rise to the surface, as when things are tossed up in winnowing-baskets; for it was in this way that an earthquake overturned the region around Sipylus and the so-called Phlegraean Plain and the region around Liguria. But in the islands out at sea earthquakes occur less than in those near the mainland; for the great mass of the sea cools the exhalations and hinders them by its weight and forces them back, and further, the sea flows and is not shaken, being mastered by the winds; and because it occupies so great a place, the exhalations do not go into it but come out of it, and the exhalations from the earth follow after these. But the islands near the mainland are a part of the mainland; for the space between, being small, has no power of its own; but it is not possible to move the islands out at sea without moving the whole sea, by which they happen to be surrounded. Concerning earthquakes, then—both what their nature is, and through what cause they come about, and concerning the other things that happen along with them—we have spoken, roughly, about the most important points.

60| Let us now speak about lightning and thunder, and further about the typhoon and the fiery whirlwind and thunderbolts; for one must suppose the same starting point for all of these. For since the exhalation, as we said, is twofold—one moist, the other dry—and the mixture has both of these potentially and is formed into cloud, as has been said before, and further, since the formation of the clouds becomes denser toward the outer limit (for at the point where the hot is separated off and departs into the region above, at that point the formation must necessarily be denser and colder)—for this reason thunderbolts and squalls of wind and all such things travel downward, even though everything hot is naturally disposed to travel upward; but the expulsion must necessarily happen in the direction opposite to the density, just like fruit-stones that leap out from between the fingers; for these too, though they have weight, often travel upward. So the heat that is separated off scatters into the region above. But as much of the dry exhalation as is enclosed within, during the change as the air is cooled, is squeezed out as the clouds come together, and being carried along by force and striking against the clouds that surround it, it produces a blow, the sound of which is called thunder. And the blow comes about in the same way—to compare a small effect to a greater one—as the sound that occurs in a flame, which some call the laughter of Hephaestus, others the laughter of Hestia, and others still a threat from these gods.

61| It occurs whenever the exhalation, gathered together, is carried into the flame, as the logs crack and dry out; for it is in this same way that, occurring in the clouds, the expulsion of wind, falling upon the density of the clouds, produces thunder. The sounds are of every kind because of the unevenness of the clouds and because of the hollow spaces between them, where the continuity of the density fails. This, then, is what thunder is, and it comes about through this cause; but the wind that is squeezed out is, for the most part, set on fire with a thin and weak burning, and this is what we call lightning, whenever the wind, as it were shooting out, is seen colored. It occurs after the blow and later than the thunder; but it appears earlier because sight outstrips hearing. This is made clear in the rowing of triremes; for the first sound of the rowing reaches one only when the oarsmen are already bringing the oars back up again. And yet some say that fire comes to be within the clouds: Empedocles says this is the sunlight that has been enclosed within, while Anaxagoras says it is fire from the upper aether—what he calls fire—brought down from above to below. They say, then, that lightning is the flashing-through of this fire, and thunder is the sound and hissing of it being extinguished within, so that, just as it appears and comes about, in this way too the lightning is prior to the thunder.

62| But the enclosure of fire is unreasonable, on both accounts, but more so the drawing-down of the aether from above. For one must state the cause of what is naturally disposed to travel upward instead traveling downward, and also why this happens in the sky only when it is cloudy, but not continuously so in that condition; and when the sky is clear, it does not happen. For this seems, in every respect, to have been said carelessly. In the same way, too, it is not persuasive to say that the heat coming from the rays, trapped within the clouds, is the cause of these things; for this account too has been stated far too casually; for the cause must always be something separated off and determinate—of thunder and lightning and the other such things—and must come about in this way. But this differs very greatly; for it would be like supposing that water and snow and hail exist within beforehand and are later separated out, and do not come to be, as though the combination were always producing each of them ready to hand. For in the same way, one must suppose those things to be combinations and these to be separations-out, so that if one of these two does not come to be but exists, the same account will fit both alike. And what would one call the enclosure any different from what happens in denser things?

63| For water too becomes hot from the sun and from fire; but nevertheless, whenever the water comes together again and is cooled as it freezes, no such expulsion as those men speak of results. And yet, in proportion to the size, the wind arising within it from the fire ought to produce a boiling, which it is not possible for it to have existed within beforehand; nor do those men make the sound a boiling, but a hissing; but the hissing too is a slight boiling; for where what falls upon it masters it as it is being extinguished, there it produces the sound by boiling. There are some, such as Cleidemus, who say that lightning does not exist but only appears to, comparing it to the case where someone strikes the sea with a rod; for the water appears to gleam at night; so too, they say, when the moisture in the cloud is struck, the appearance of the brightness is the lightning. These men, then, were not yet familiar with the doctrines about reflection, which seems to be the cause of such an effect; for the water appears to gleam when struck because sight is reflected off it toward one of the bright objects. For this reason this happens more at night; for by day it does not appear, because the greater brightness of the day makes it disappear.

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