Aristotle · a new plain-English translation from the original language
1| Problems Concerning Air. Why do limbs shut inside inflated wineskins cause pain? Is it because of the pressure of the air? For just as the air does not yield to those pressing the skin from outside, but pushes back, so too the air presses on whatever is caught inside it. Or is it because the air is held by force and compressed? Straining outward on every side in accordance with its nature, it then presses hard against the body caught within it.
2| Why, in the marshes beside rivers, do the creatures called "bull-bellowers" occur, which are said in myth to be bulls sacred to the god? The sound that occurs is like the voice of a bull, so that cows are affected on hearing it just as if a bull were bellowing. Is it because this occurs in rivers that pool into marshes, or in marshes that stand stagnant, or are checked by the sea, or that release their air more all at once — is it in such places that this happens? The cause is that hollows form in the earth. So the water, being churned in this way — since there is a current within such a pooling — pushes the air out through a narrow opening into a wider hollow, just as if someone made a noise at the mouth of an empty jar, it becomes like a bellow; for in cattle too the bellowing comes about because of this shape. And the shapes of the hollows, being uneven, produce many strange sounds besides, since if one removes the base of a jar and rubs it, pulling in and out through the bottom — if one rubs through the binding — it makes a noise, so that wild animals flee, whenever orchard-keepers construct this device. Why is air not wet, though it touches water? For of other things, nothing that touches water fails to become wet. Is it because their outer surfaces meet together, and the plane surface of each is not a distinct one? Now other things are heavier, but air does not sink below the water's surface. So it touches the water, because nothing lies between them, but it is not wetted, because it is always above the water.
3| Why does calm, fine weather occur especially at midnight and at midday? Is it because calm is a standing-still of the air, and it stands still especially when the air is either mastering or being mastered, while it moves when the two are fighting? Now it masters especially at midnight, and is mastered at midday; for at one time the sun is farthest away, and at the other nearest. Further, winds begin either around dawn or around sunset, and the one from dawn ceases when it is mastered, while the one from sunset ceases when it stops mastering. So it turns out that some winds cease at midday, and others at midnight. Why, when dawn is just breaking and it is already early morning, is it colder than at night, although the sun is nearer to us then? Is it because toward daybreak dew and frost fall, and these are cold; so it is as if the whole region were sprinkled with cold moisture, and a general chilling results? Why does the region of the Black Sea have both the greatest cold and the greatest stifling heat? Is it on account of the thickness of its air? For in winter the air cannot be thoroughly warmed through, while in summer, once it is heated, it burns because of its thickness. And the same cause explains why marshy places are cold in winter but hot in summer. Or is it because of the sun's course? For in winter the sun is far off, and in summer it is near.
4| Why is the sky clearer at night than by day? Is the sun the cause of both wind and disturbance? For these come about when some motion has occurred, and the cause of that motion is heat. So when heat is not present, everything is at rest, more so than when the sun is rising — the opposite case. And as to why this clearness is perhaps never found coming from the mainland: it is because where there is the most motion, there a thing would least remain and hold together, since what is forming is not uniform and does not prevail. In winter, then, the sea is such a place of motion, and in summer, the land.
5| Why is it that when liquid is poured out into wineskins, the wine-jar does not only take in the liquid together with the skins, but also takes in something extra? Is it because air is present within the liquid? This air, then, when it is inside the jar, cannot be squeezed out because of the size of the jar; for it is harder to press anything out of a larger thing, whether liquid or breath, than out of a smaller — as with sponges. But when the liquid is divided up into small portions, the air is squeezed out of the skin along with what is in it, so that the place the air occupied becomes empty. That is why the jar takes in the skins and, further, still more liquid. And this happens more with wine, because there is more air present in wine than in water. Similar to this is the fact that the same vessel can take ash and water together in a quantity greater than each poured in separately would occupy. For the ash evidently has many empty spaces within it. Being finer, then, the water works its way through more and packs the ash down, so that it becomes compressed — and this is because the packing occurs part by part (for a thing is packed more tightly when it is packed a little at a time than when packed all at once), and as this happens the ash settles further down;
6| and at the same time the ash also takes the liquid into itself, because it has hollow spaces. And the ash, being hot when thrown into the water, cuts through it and turns it into vapor. And the same thing happens whether the water is poured in first and the ash falls in afterward, or the reverse — so that the water too would have hollow spaces and empty gaps within itself. Or is it not the water that receives the ash, but the ash that receives the water? For it is reasonable that what is finer in its parts is what enters in. This is also clear from experience. For when the ash is sprinkled in, the rest of the water flows together toward the spot where it is sprinkled — whereas the opposite ought to happen, if it were the water that was doing the receiving. Or does this not happen if the water is poured in first and thoroughly fills the space? But if anything at all is then added, it overflows. And if it once overflows and the ash then falls on top, this result does occur — for it was the ash that was doing the receiving. The same thing explains why pits do not take back the earth that was dug out of them: it seems that some air has taken possession of the space beforehand, and this is why they do not receive it. Why does air, although thicker than light, pass through solid bodies? Is it because light travels only in a straight line — which is why sight cannot see through porous things, such as pumice stone, since the pores in it do not line up, though it can see through glass — whereas air is not blocked, because what it passes through need not run in a straight line?
7| Why does air become cold from contact with water, but not thoroughly wet, even if one blows very hard into the water so as to make it churn — while the fact that it is cold is shown by its shifting away, for it cools things coming from the water? Is it because air is naturally disposed to be both cold and hot, so that it changes, to the touch, whatever it comes in contact with, but it is never made wet, because it is lighter? And it never goes down into the depth of the water, but always keeps to the surface, even if forced downward — and the water itself moves further down still, so that the air never goes down into the depth. Why does the air that rises up out of bubbles come out dry? Is it because the liquid does not stay on it, but the water slides off? And what remains on the bubble is too little to make it wet. Why does air not become saturated, but water does? For even when it is turned into air, it is still wet. Is it because it is not the case, just as it is not the case with stone either? For not everything is capable of being saturated, but only what is sticky or wet. ...or is it because air travels upward? For a wineskin, when empty, travels downward, but when it is inflated, it stays up, because the air carries it upward. But if air lightens things and prevents them from moving downward, why do things become heavier when inflated? And how is it that at one time, when a thing is heavier, it stays up, but when it becomes lighter, it moves down?
8| Why does air ...not travel upward? For if winds arise from air being set in motion by heat, and fire is naturally disposed to travel upward, then the wind too ought to have gone upward, given that both what moves it goes upward and what is moved is naturally disposed to travel in that same way. But as it is, wind evidently makes its motion slantwise. Why is the air from the east colder than that from the west? Is it because the one is nearer to midnight, the other to midday? Midday is the hottest time because it is nearest to the sun, while midnight is colder for the opposite reason. Why are nights more stifling than days during heat waves? Is it because of the absence of wind? For the etesian winds and their forerunners blow less at night. Why do things in wineskins not rot, when the skins are inflated, and likewise things in sealed containers? Is it because things rot when they are in motion, while everything that is full is motionless, and these things are full? Why is there more cold when the sky is clear than when it is overcast, given that the stars and the heavens are hot? Is it because in clear weather nothing holds back the vapor, but it disperses, whereas when it is overcast the vapor is held back? And the same holds for north winds versus south winds, and for the same reason: for the south wind draws such vapor along, while the north wind pushes it away. And vapor evidently rises more in north winds than in south winds, and more in winter than in summer. Or is this due to some dissimilarity? Or is it because vapor occurs when something hot is being cooled?
9| Why is a smaller volume of air hotter than a larger one? For confined spaces are warmer. Is it because the larger volume moves more, and motion produces cold? A sign of this is that hot things grow cold when set in motion. Why do water and earth rot, but air and fire do not? Is it because everything that rots becomes extremely hot, and nothing is hotter than fire? Or is it because a thing must first be cooled, whereas fire is always hot, and air is full of fire? Nothing rots while hot, but only once it has been cooled; earth, water, and air all become both hot and cold. Why are overcast days warmer than clear ones? Is it, as the ancients used to say, because the stars are cold? Or is that altogether absurd, and is it rather because vapor rises? It should also be noted that dew and frost form when there is no wind. So when the sky is clear, the heat disperses out, and it is this that draws up the moisture, so that the air is cold; that is why moisture given off from the heat forms dew. But when the sky is overcast, the heat is held back, so that neither dew nor frost forms when it is overcast. So the heat, remaining down near the earth, produces the warmth.
10| Why does the air stir back and forth in the upper parts of houses, especially in calm weather? Is it because air, in its composition, is full of empty spaces? So when it begins to flow inward, the air already in the room yields and contracts. As this happens, over time the air outside becomes fuller of empty space, and comes to occupy a great deal of room. Into this space, then, the air from the room falls, being close by, and is carried into this space because it hangs there and the nature of the void cannot resist it. And as this happens in many parts of the outside air at once, the neighboring air follows it because of the way they face each other; then, as a great deal flows in from outside, the inner region becomes full of empty space, and the outer region denser, and the flow again passes from inside to outside. And these movements keep alternating.