by Aristotle
11 · Why is the air from bubbles and the air which comes up from beneath [25] the water never wet? Is it because the moisture is not retained, but the water drops off? The water on the surface of a bubble is also too little to moisten anything.
12 · Why is it that air cannot saturate anything, but water can? For water even when it is transformed into air is moist. Is it for the same reason as that for [30] which stone cannot do so? For everything has not this faculty of saturating other things, but only that which is viscous or liquid.
13 · … Is it because the air in it is carried upwards? For when the skin is empty it sinks; but when it is inflated, it remains on the surface, because the air supports it. But if the air makes it lighter and prevents it from sinking, why does a [35] skin become heavier when it is inflated? And how is it that when it is heavier it floats, and when it is lighter it sinks?
14 · Why is it that the air does not rise upwards? For if the winds are the [939b1] result of air being moved by heat and it is the nature of fire to rise upwards, the wind ought to travel upwards, since that which sets it in motion rushes upwards and that which is set in motion has a natural tendency to travel in the same direction. As a matter of fact, however, the air obviously travels in an oblique direction.
[5] 15 · Why is the hour of dawn colder than the evening? Is it because the former is nearer to midnight and the latter to midday? Now midday is the hottest time, because it is nearest to the sun, and midnight is colder for the opposite reason.
16 · Why is it that in hot weather the nights are more stifling than the days? [10] Is it owing to the absence of wind? For the periodical winds and the ‘forerunners’ blow less at night.
17 · Why is it that substances enclosed in inflated skins and closely covered vessels remain uncorrupted? Is it because things which are in motion become corrupt, and all things that are full are without motion, and such skins and vessels are full?
[15] 18 · Why is it that it is colder when the sky is clear than when it is overcast, though the stars and the heaven are warm? Is it because in clear weather there is nothing to hold the vapour, but it is diffused everywhere, whereas in cloudy weather it is contained? For the same reason it is colder when the wind is in the North than when it is in the South; for the South wind attracts cloud, whereas the North wind [20] dispels it, and more evaporation appears to take place when the wind is in the North than when it is in the South, and in winter than in summer. Or is it because of dissimilarity? Or because vapour is formed when that which is hot cools?
19 · Why is it that a smaller amount of air is warmer than a larger quantity (for confined spaces are always warmer)? Is it because a larger quantity is [25] subjected to more motion, and motion makes a thing cold? This can be seen from the fact that hot things become cold if set in motion.
20 · Why is it that water and earth become corrupt, but air and fire do not? Is it because anything which is corrupted must become very hot, but there is nothing hotter than fire? Or is it because a thing must be chilled before it can be corrupted, [30] but fire is always hot and the air is full of fire? So nothing becomes corrupted when it is hot, but only when it is chilled. Now earth and water5 can become hot and cold.
21 · Why is cloudy weather hotter than clear weather? Is it because, as the men of old said, the stars are cold? Or is this too absurd a doctrine, and is the real reason that in clear weather vaporization takes place? That this is so can be inferred [35] from the fact that, when there is no wind, dew and hoar-frost are formed. When, therefore, the weather is clear, the hot substance, by which the moisture is taken up, is blown about, and so the air becomes cold; for which reason also the moisture which the hot substance lets fall forms dew. But when the weather is cloudy the moisture is contained; and therefore there is no dew or hoar-frost in cloudy weather. [940a1] The heat, therefore, remaining in the neighbourhood of the earth makes the weather warm.
22 · Why is it that in lofty rooms the air constantly ebbs and flows, especially in calm weather? Is it because the air contains much void in its composition? When, therefore, it begins to flow in, the air inside the room gives way [5] and contracts; and when in course of time this air becomes massed together, the air outside becomes more full of voids and contains much vacant space. Into this space then the air from the room rushes, since it is near at hand, and passes into it, because it is suspended and the nature of the void cannot resist. So when this happens in [10] many parts of it, the adjoining air follows it owing to the forward impetus;6 and then, since a large quantity of air rushes out,7 the space within becomes full of voids, while the air outside is denser and so rushes in again from outside. Thus these two currents continually interchange. [15]
BOOK XXVI
PROBLEMS CONNECTED WITH THE WINDS
1 · Why does the North-East wind (Caecias) alone of the winds attract the clouds to itself? Is it because it blows from higher regions? For the parts towards the East are higher than those towards the West, as is shown by the extent and [20] depth of the sea towards the West. Now Caecias, blowing from above to a contrary direction, describes in its course a line which follows an upward curve in relation to the earth;1 and falling, as has been said, upon the western regions of the earth and massing the clouds together as a result of the form of line which it follows, on its [25] return it thrusts the clouds before it towards itself. It is the only one of all the winds which does this, because for some the opposing regions are higher,2 towards which their course, either starting from a lower level or proceeding in a straight line, as a result travels in a downward curve3 towards the earth, so that there can be no return [30] of the wind to its source because it ends its course round the earth, where, besides, there are no clouds.4 The East wind (Apeliotes) and the other winds which follow a less curving course do not form clouds because they have no moisture. Since, then, it forms no clouds, the effect produced by the East wind (Apeliotes) is less obvious than that produced by Caecias.
[35] 2 · Why do the North winds occur at a fixed period of the year, whereas the South winds do not? Or do South winds occur annually but are they not continuous, because the source of the South wind is far away from us, and we live close to the North wind? Further, the annual North winds blow when the air is still (for they [940b1] blow in summer); whereas the South winds occur in the spring, when the region of the air is less stable. Again, the South wind is moist, and the upper region of the atmosphere is unfavourable to moisture; so any moisture which is formed in it is quickly dissolved. Also moisture is erratic; and so the South wind, because it does [5] not remain in the same place, helps to set up changes in the movement of the air. And since the air does not remain in the same place when it moves, other winds are consequently set up; for a wind is a movement of air.
3 · Why does the South wind blow after a hoar-frost? Is it because hoar-frost occurs when concoction takes place, and after concoction and cleansing a change to [10] the opposite condition takes place? Now the South wind is the opposite of the North wind. For the same reason also the South wind blows after snow. In a word, both snow and hail and rain and all such processes of cleansing are a sign of concoction; [15] therefore after rain and similar storms the winds fall.
4 · Why do the alternating winds blow? Is it for the same reason as causes the change of current in straits? For both sea and air are carried along until they flow; then, when the land-winds encounter opposition and can no longer advance, because the source of their motion and impetus is not strong, they retire in a [20] contrary direction.
5 · Why do the alternating winds come from the sea? Is it because the sea is close at hand? Or is it because the alternating wind is the opposite of the land-wind and as it were the reverse of it? Now the land-wind is the breeze which blows from [25] the land towards the sea, and the alternating wind is the reflux of the land-wind, so that it must necessarily come from the sea. Or is it because the air which has been set in motion collects out at sea? The reason of its not collecting on land and of its being thrown back
is the fact that the sea is in a hollow, and air, like water, flows always into the deepest hollow it can find.
[30] 6 · Why do cloud-winds stop sooner when rain falls? Is it because, when it rains, the hollows of the cloud, in which the source of the wind is formed, collapse?
7 · Why are not the same winds everywhere rainy? Is it because the same winds do not everywhere blow against mountains, but different winds are opposed to different mountains? For example, when the winds blow laboriously against [35] steep mountains, the clouds are more likely to form there, since the wind cannot push them farther forward; and when the clouds form and are compressed, they burst.
8 · Why are sunsets, if they are clear, a sign of fine weather; if they are [941a1] disturbed, a sign of stormy weather? Is it because a storm occurs when the air is dense and thick? When, therefore, the sun prevails, it breaks up and clears the air; but, if it is itself overpowered, an overcast sky results. If, therefore, the density is [5] excessive, a storm occurs as soon as the day dawns; whereas if it is weaker but not completely overpowered, the denseness which forms is driven towards the setting sun and remains there, because the air round the earth is thicker than the storm. And the rest of the air quickly densifies, because a beginning of the process has already been made and there is a rallying point to receive and collect anything [10] which comes to it,5 the same thing occurring in the air as happens in a rout, where, if one man makes a stand, the rest also remain firm. Hence the sky sometimes becomes quickly and suddenly overcast. When, therefore, there is a disturbed sunset, it is a strong indication that the sun has not got the mastery over the density, [15] though it has struggled long against it, so that probably further condensation has taken place. This is a less alarming symptom when it occurs after a storm than in calm weather; for in the former circumstances it is probably the remnant of a storm, but in the latter the beginning of condensation.
9 · What is the origin of the saying, [20]
Boreas blows not at night when once the third sun has arisen?
Is it because the breezes which come from the north are weak when they blow at night? A proof that the amount of air which is set in motion is not great is the fact that they blow at a time when there was a small amount of heat; and a small amount of heat was moving a small amount of air. Now all things terminate in multiples of three, and things which are very small terminate at the end of the first triad; and [25] that is what this wind does.
10 · Why does the North wind blow more frequently than the South wind? Is it because the North wind, being near the inhabited portion of the world, attracts our notice in spite of its short duration (for it is with us as soon as it begins to blow), whereas the South wind does not reach us, because it blows from a distance? [30]
11 · Why does the South wind blow as much6 on winter nights as on winter days? Is it because during the night the sun is near the southern region, and the nights there are warmer than are the days in the north? Much air, therefore, is set in [35] motion and not less than by day; but the warmer days prevent the wind from blowing more strongly by drying up the moisture.
12 · Why does the South wind blow at the time of the dog-star, and why does this happen regularly like any other natural phenomenon? Is it because the southern regions are warm, since the sun is not far7 away, and so the evaporation is considerable? The South winds would blow frequently if it were not for the annual [941b1] winds; as it is, these prevent their blowing. Or is it because a sign occurs at the setting and rising of any star, and especially of the dog-star? It is clear that winds blow most of the time of and after its rising, and since it causes stifling heat, it is [5] only natural that the hottest winds should be set in motion when it rises; and the South wind is hot. And since things are most accustomed to pass from contraries into contraries, and the ‘forerunners’, which are northern winds, blow before the rising of the dog-star, the South wind naturally blows after the dog-star appears, [10] since a sign then occurs, and the occurrence of a sign8 at the time when stars rise means a change in the air. Now all winds change either into their contraries or into those on their right; but since the North wind cannot9 change into the winds on its right, the only thing left for it to do would be to change into a South wind. Now on the fifteenth day after the winter solstice the wind is in the south, because the [15] solstice marks as it were a fresh start and the sun sets in motion air which is nearest to it10 and at this solstice it is near the south. Just as, therefore, when it sets the region of the east in motion it stirs up the East winds, so when it sets in motion the southern region it stirs up the South winds. It does not do this immediately after the [20] solstice, because the changes which it sets up extend at first over a very small area, but only on the fifteenth day, because this date corresponds to the first sensible impression made by the change; for the said date is simply the most significant part of a whole.
13 · Why are the days most changeable during the period of Orion, and why [25] is there then such variability in the wind? Is it because during a period of change all things are always most indeterminate, and Orion rises at the beginning of autumn and sets in the winter, so that, since there is not yet one settled season, but one is coming on and the other coming to an end, the winds must therefore necessarily be [30] unsettled, because those of each season are passing into one another? And Orion is said to be dangerous both in his setting and in his rising owing to the uncertainty of the season; for it must be full of confusion and inconsistency.
14 · Why does the North wind which blows at night cease on the third day? [35] Is it because it comes from a small and weak source and the third day marks the crisis? or is it because it expends itself all at once like the cloud-winds, and therefore quickly dies down again?
15 · Why do the North winds blow more than the other winds? Is it owing to the fact that the inhabited portion of the earth is near the region of the north, which is high and outside the tropics and full of snow, which never leaves some of the [942a1] mountains? As, therefore, frozen matter is usually melting there, a wind often arises, and this wind is the North wind which comes from the region of the pole.
16 · Why do the South winds blow during winter and at the beginning of [5] spring and the end of the autumn, and why are they boisterous and whirling in their course and why are they cold to the inhabitants of Libya in like manner as the North winds are to us? Is it because, the sun being near, the winds must necessarily be set in motion? Now during the winter the sun travels towards the south, and at the beginning of the spring and at the end of autumn it is giving forth heat; whereas [10] during the summer the sun travels towards the north and leaves those other regions. The South wind is hot, because it mingles its breath with the air in the region of Libya, which is hot; and so it is boisterous and makes the summer rainy, sweeping down on the sea. [15]
17 · Why does the South wind cause evil odours? Is it because it makes bodies moist and hot, and they are then most liable to corruption? South winds, however, which come from the sea are good for plants—for it falls on them from the sea, as it does on the Thriasian Plain in Attica—and the reason is that it is cooled before it arrives.11 Now mildew is caused by moisture which is hot and comes from [20] without.
18 · Why does wind usually occur before eclipses, at nightfall before midnight eclipses and at midnight before those which occur at dawn? Is it because the heat which comes from the moon becomes faint, because its course is already [25] getting near the earth, and when it is quite near the eclipse will take place? Now when the heat, by which the air is held back and kept still, is set free, the air begins to move again and a wind springs up later in time according as the eclipse is later.
19 · Why is the South wind rainy not when it is beginning but when it is ending? Is it because it collects the air from a distance? For the rain comes when the [30] South wind masses the air together, and it masses the air together only after it begins to blow. Or is it because, when the South wind begins to blow, the air is still hot, because it comes from a ho
t region, but in course of time it becomes cool, and then tends to become massed into rain?
20 · Why is it that the South wind, when it is less strong, brings clear weather, but, when it is strong, brings clouds and lasts longer? Is it, as some say [35] owing to the source from which it comes? For if it comes from a weaker source it brings clear weather, but if it starts from a stronger source it brings clouds. Or is it because it is weaker when it begins, so that it does not propel much air, but in the [942b1] end it usually becomes strong? Hence comes the proverb,
When the South wind begins and when Boreas ceases his blowing.
21 · Why is it that in the winter the winds come forth from the east, but in the summer also from the west? Is it because, when the sun no longer prevails, the [5] air flows freely? When, therefore, the sun sinks, it leaves clouds behind it, which cause the West winds, and anything which it carries with it to the inhabitants of the southern hemisphere becomes an East wind. And, contrariwise, when it sinks in the southern region of the earth, it will cause West winds for the inhabitants of that [10] region and East winds in our part of the world from the air which accompanies it. For this reason too, if it finds another wind blowing, that wind becomes stronger when the sun rises, because it adds something to it.