Lecture 10 — The south wind not from the antarctic but from the summer tropic.
But the south wind blows from the tropic of Cancer and not from the antarctic region.
There are two inhabitable sections of the earth: one near our upper, or nothern pole, the other near the other or southern pole; and their shape is like that of a tambourine. If you draw lines from the centre of the earth they cut out a drum-shaped figure. The lines form two cones; the base of the one is the tropic, of the other the ever visible circle, their vertex is at the centre of the earth. Two other cones towards the south pole give corresponding segments of the earth. These sections alone are habitable. Beyond the tropics no one can live: for there the shade would not fall to the north, whereas the earth is known to be uninhabitable before the sun is in the zenith or the shade is thrown to the south: and the regions below the Bear are uninhabitable because of the cold. (The Crown, too, moves over this region: for it is in the zenith when it is on our meridian.)
So we see that the way in which they now describe the geography of the earth is ridiculous. They depict the inhabited earth as round, but both ascertained facts and general considerations show this to be impossible. If we reflect we see that the inhabited region is limited in breadth, while the climate admits of its extending all round the earth. For we meet with no excessive heat or cold in the direction of its length but only in that of its breadth; so that there is nothing to prevent our travelling round the earth unless the extent of the sea presents an obstacle anywhere. The records of journeys by sea and land bear this out. They make the length far greater than the breadth.
If we compute these voyages and journeys the distance from the Pillars of Heracles to India exceeds that from Aethiopia to Maeotis and the northernmost Scythians by a ratio of more than 5 to 3, as far as such matters admit of accurate statement. Yet we know the whole breadth of the region we dwell in up to the uninhabited parts: in one direction no one lives because of the cold, in the other because of the heat. But it is the sea which divides as it seems the parts beyond India from those beyond the Pillars of Heracles and prevents the earth from being inhabited all round.
Now since there must be a region bearing the same relation to the southern pole as the place we live in bears to our pole, it will clearly correspond in the ordering of its winds as well as in other things. So just as we have a north wind here, they must have a corresponding wind from the antarctic. This wind cannot reach us since our own north wind is like a land breeze and does not even reach the limits of the region we live in. The prevalence of north winds here is due to our lying near the north. Yet even here they give out and fail to penetrate far: in the southern sea beyond Libya east and west winds are always blowing alternately, like north and south winds with us. So it is clear that the south wind is not the wind that blows from the south pole. It is neither that nor the wind from the winter tropic. For symmetry would require another wind blowing from the summer tropic, which there is not, since we know that only one wind blows from that quarter. So the south wind clearly blows from the torrid region. Now the sun is so near to that region that it has no water, or snow which might melt and cause Etesiae. But because that place is far more extensive and open the south wind is greater and stronger and warmer than the north and penetrates farther to the north than the north wind does to the south. The origin of these winds and their relation to one another has now been explained.
199. Because in solving the foregoing doubt the Philosopher had posited that the south winds do not blow uninterruptedly after the winter solstice, as do the northern winds after the summer solstice, and because the reason he assigned supposed that southern winds do not blow from regions of much water and snow (which would be false, if the south wind should blow from the other pole, where there is also an abundance of such matter, as has been said above), he therefore now intends to show that the south wind does not blow from the other pole but from a place under the summer tropic. About this he does three things:
first, he proposes what he intends (362a31);
second, he outlines the disposition of the habitable earth, to enable one to better understand what he intends, at there are two inhabitable sections of the earth (362a32);
third, he manifests what he proposes, at now since there must be a region bearing the same relation to the southern pole (362b30).
He says therefore first that the south wind blows toward us from the summer turning (362a31), i.e., from the place under the summer tropic, namely, under Cancer, and not from the other Bear, i.e., from the other pole, concealed from us. He uses this terminology because the arctic pole, which is visible to us, is the one around which the constellations of the Bear, Big and Little, rotate.
200. Then when he says, there are two inhabitable sections of the earth (362a32), he shows the disposition of the habitable earth.
First, he shows that the shape of the habitable earth is as a drum (362a32);
second, he dismisses a contrary opinion which some held, at so we see that the way in which they now describe the geography (362b12).
He says therefore first (362a32) that there are two zones that can be inhabited: one toward the upper, arctic, pole, in which we live; the other, toward the opposite pole, south of us, just as our habitable area is south to them. But whether that land is inhabited, he leaves unclarified. The shape, however, of both areas resembles a drum. How this is to be imagined must be gathered from the facts he gives.
For it is plain that a certain portion of the heavenly sphere is always visible to us, namely, from the arctic pole to a zone which is less and less the closer one gets to the opposite pole. Another portion of the heaven is forever invisible to us, namely, from the opposite pole to a certain amount, whose size increases the closer one gets to the arctic pole. Midway between the two poles is the equinoctial circle [equator] intersected by the Zodiac declining toward each region. Where, therefore, the Zodiac declines most from the equinoctial circle toward the arctic pole is the summer tropic, i.e., the beginning of Cancer; where it declines most toward the pole invisible to us is the winter tropic, i.e., the beginning of Capricorn. This, then, is the third region of the heavenly sphere, namely, the one between-the two tropics.
Two other parts are considered: one between the summer tropic and that which is always visible to us, and the one between the winter tropic and that which is hidden to us of the heaven. And because the whole earth is spherical, and located in the center of the heavenly sphere, it is necessary that under each part of the heavenly sphere there be considered individual parts of the terrestrial sphere. Let A mark the terrestrial point under the arctic pole; let B mark the point under the limit of the part always visible to us; let C represent the point under the summer tropic; let D mark the point under the winter tropic, let E represent the point under the limit of the part always hidden; let F mark the point under the antarctic pole, and Z the point in the center of the earth. Now draw straight lines from the center of the earth, Z, to B and to C. [The lines ZB and ZC] form two angles with a line drawn on the surface of the earth, which angles he here calls cones. Because the line on the surface of the earth is curved—for the earth is spherical—it is plain that the two aforesaid lines [ZB and ZC] produce the figure of a drum, cutting the surface of the earth in a non-circular figure.
This is what he [Aristotle] says: such a shape, i.e., that of a drum, for the inhabitable earth, is cut out by two lines proceeding from the center of it, i.e., of the earth, and they form two cones, i.e., two angles, with a line traced under the surface of the earth, the base of one angle being the tropic, i.e., having its base in the tropic point, and the base of the other, the ever visible, i.e., the other angle is at the limit of the part of the heavens always visible; the vertex, however, i.e., the top of the triangle ZBC, whose base is BC, is produced in middle of the earth, i.e., in the center. In the same way, in the other direction, toward the lower pole, two lines cut that part, drawn, namely, from the center to D and E.
And these two are the only zones that are habitable. For the zone between the two tropics seems uninhabitable because of the immense heat, as the sun passes, as it were, directly over it and over the tops of the heads of the inhabitants, if it should be inhabited. As for the other two zones, under the part of the heaven always visible and under that always hidden from us, near both poles, these are uninhabitable because of the immense cold, due to distance of the sun. That the zone beyond [i.e., below] the summer tropic is not inhabited, he shows from the fact that, if it were, it would not be true that for all men living toward the arctic pole, shadows fall toward the north. For if the sun should sometimes be between them and the north, a shadow would fall sometimes towards the south. But if anyone lived beyond [below] the summer tropic, toward the arctic pole, then, when the sun is in the summer tropic, it would be between them and the arctic pole; hence a shadow would fall for them toward the south. But it is not found in inhabitable regions either that a shadow disappear or shift to the south. For there is no shadow where the sun is directly overhead, so that no shadow can be produced in any direction, while a shadow falls to the south in places where the sun declines more to the north.
And he says that such places are uninhabitable, because even though someone should live there on account of some favorable combination of waters or mountains, yet such dwellings are rare and oppressive. Just as these places are uninhabitable on account of the excessive heat, so the regions under the constellation of the Bear [which is the part of the heaven always visible to us] are uninhabitable on account of the cold caused by the sun being far away. Hence that part of the earth in which we live is between the two circles, i.e., between the one that passes through the summer tropic and the one which bounds that part of the heaven always visible to us. And this is plainly evident from the fact that the constellation of the Crown, which, indeed, is between both these circles, appears directly over our heads, when it is in the meridian circle, i.e., in the circle that passes through the poles of the world and the point directly overhead.
201. Then when he says, so we see that the way in which they now describe the geography (362b12), he dismisses a false theory upheld by some. And he says that the foregoing account shows how ridiculous they are who describe the inhabited earth as circular: for such a thing is seen to be impossible, both according to reason and according to evident signs. For reason shows that the inhabited portion of earth is limited to a width, bounded on one side by a zone uninhabitable on account of the heat, and on the other by a zone uninhabitable on account of the cold. But along its length a circle could be joined, in such a way that all the aforesaid area would be inhabited, on account of the temperate climate; for no excess of heat and cold is found in the directions of east and west—according to which the earth's length is measured—but only according to width, which is reckoned according to the distance from the pole to the equinoctial circle [equator], since, on a surface the greater dimension is called the length, and the smaller one the width, and from east to west there is designated a whole semicircle, while from the arctic pole to the equator, a quarter part of a circle. It is reasonable also that a distance to east and west should not cause differences of heat and cold, because this does not produce a greater or lesser approach to the sun's path as is produced by distance in latitude. Hence, if the mass of the sea did not somewhere prevent it, the whole course from west to east, and again from east to west, would be traversable, since the whole appears temperate. However, we find the earth inhabited only in a semicircular zone running from east to west; the extent of the sea preventing our access to the other semicircle. Thus does reasoning sufficiently show that the habitable surface of the earth is not circular or spherical.
And this is also made evident from manifest signs based on sea and land journeys: there is a great difference in quantity between longitude and latitude; consequently, the surface area that is habitable is not in the shape of a sphere. That there is such a great difference is plain: for from the Pillars of Hercules, which are at the final confines of Spain, as though at the last border of the west, to the Tanais in India, the distance (which is longitude) exceeds in size the distance from the last borders of Ethiopia to the extreme regions of Scythia (which is the latitude of our habitable earth), by a ratio of more than 5 to 3. If anyone were to analyze sea and land voyages in the proper way, he would have no doubt about these distances. But the habitable earth has the following differences respecting longitude and latitude — for we know that all of the inhabitable area of the earth according to latitude is inhabited up to the uninhabitable areas, which are not inhabited either on account of the cold or on account of the heat; but this is not so of the longitude, because the area around the Indian limit to the east, and that around the Pillars of Hercules to the west, do not seem to be able to be conjoined so as to return in another direction, making the whole of this portion of the earth continuously habitable, because access is forbidden by the sea. That is why we cannot know whether people live there or not.
202. Then when he says, now since there must be a region bearing the same relation to the southern pole (362b30), he proves his proposition about the source of the south wind. About this he does three things:
first, he shows that the south wind does not blow from the other pole;
second, that it does not blow from the winter tropic, but from the summer tropic, at it is neither that nor the wind (362b30);
third, he accounts for the vehemence of the south wind, at now the sun is so near to that region that it has no water (362b30).
He says therefore first (362b30) that just as the area of the earth in which we live is related to the arctic pole, so must some other be related to the opposite pole. Hence the blowing of winds in that area must be analogous to their blowing here. Then just as the north wind blows from the arctic pole, so a wind must blow there from the opposite pole (which he calls "the other Bear"). But the wind which blows from the other pole cannot reach to here, because the north wind not only cannot reach the other inhabitable part of the earth, but it cannot even reach all of our habitable area: for the north wind is apogeious, and cannot advance very far. But since our habitable area is to the north, very many north winds blow upon us; but just as many north and south winds blow here, so beyond the Sea of Libya, which is to the south, blow many east and west winds. Consequently, it is plain that the south wind does not blow from the other pole.
203. Then when he says, it is neither that nor the wind (362b30), he shows that it does not blow from the winter tropic, because if the south wind blew from the winter tropic, there would have to be another wind blowing from the summer tropic, since those two places proportionately correspond. But this does not happen: for only one wind blows on us from that direction. For this reason it is necessary that the south wind is a wind blowing from the summer tropic, where the region is torrid.
204. Then when he says, now the sun is so near to that region that it has no water (362b30), because he had previously assigned the cause of the vehemence of the north and south wind by assuming that
Continuation of the Commentary by an Unknown Author
they blew from the opposite poles, according to the opinion of others, which he has just assailed, therefore he now gives the true cause of the south wind's vehemence according to his own opinion.
He says, therefore, that, although in that region, i.e., under the summer tropic, there is a scarcity of smoky matter in comparison to the pole, because the nearness of the sun forbids the presence of much water or "pastures," i.e., grassy and moist places from which Etesiae, i.e., continuous winds, can arise, yet that region is so vast that it receives from various localities a collection of material suitable for a south wind, which wind is stabler and stronger than the north wind, on account of the size of the places from which its abundant matter has been collecting for a long time. As a consequence, this wind can last longer and reach the place of the north wind, more than the north wind can reach there, i.e., the place of the south wind.
Lecture 11
On the order and contrariety of winds
Let us now explain the position of the winds, their contraries, which can blow together with which, and which cannot, what they are and how many, and any other of their passions that have not been treated in the particular Problems. What we say about their position must be followed with the help of a description.
For clarity's sake, we have drawn the circle of the horizon, which is round, but it represents the zone in which we live; for that can be divided in the same way.
Let us also begin by laying down that those things are locally contrary which are locally most distant from one another, just as things specifically most remote from one another are specific contraries. Now things that face one another from opposite ends of a diameter are locally most distant from one another.
Let A be the point where the sun sets at the equinox and B, the point opposite, the place where it rises at the equinox. Let there be another diameter cutting this at right angles, and let the point D on it be the Bear and its diametrical opposite C the south. Let H be the rising of the sun in the summer and F its setting in the summer; G its rising in the winter, and E its setting in the winter. Draw a diameter from H to E from G to F.
Then since those things are locally contrary which are most distant from one another in space, and points diametrically opposite are most distant from one another, those winds must necessarily be contrary to one another that blow from opposite ends of a diameter.
The names of the winds according to their position are these. Zephyrus is the wind that blows from A, this being the point where the sun sets at the equinox. Its contrary is Apeliotes blowing from B, the point where the sun rises at the equinox. The wind blowing from D, the north, is the true north wind, called Boreas and Aparctias: while Auster blowing from C is its contrary; for this point is the south and C is contrary to D, being diametrically opposite to it. Caecias blows from H, where the sun rises at the summer solstice. Its contrary is not the wind blowing from F but Lips blowing from E. For Lips blows from the point where the sun sets at the winter solstice and is diametrically opposite to Caecias: so it is its contrary. Eurus blows from G, coming from the point where the sun rises at the winter solstice. It borders on Notus, and so we often find that people speak of 'Euro-Noti'. Its contrary is not Lips blowing from E but the wind that blows from F which some call Argestes, some Olympias, and some Sciron. This blows from the point where the sun sets at the summer solstice, and is the only wind that is diametrically opposite to Eurus. These are the winds that are diametrically opposite to one another and their contraries.
There are other winds which have no contraries. The wind they call Thrascias, which lies between Argestes and Aparctias, blows from C; and the wind called Meses, which lies between Caecias and Aparctias, from K. (The line CK nearly coincides with the ever visible circle, but not quite.) These winds have no contraries. Meses has not, or else there would be a wind blowing from the point M which is diametrically opposite. Thrascias corresponding to the point G has not, for then there would be a wind blowing from N, the point which is diametrically opposite. (But perhaps a local wind which the inhabitants of those parts call Phoenicias blows from that point.) These are the most important and definite winds and these their places.
There are more winds from the north than from the south. The reason for this is that the region in which we live lies nearer to the north. Also, much more water and snow is pushed aside into this quarter because the other lies under the sun and its course. When this thaws and soaks into the earth and is exposed to the heat of the sun and the earth it necessarily causes evaporation to rise in greater quantities and over a greater space.
Of the winds we have described Aparctias is the north wind in the strict sense. Thrascias and Meses are north winds too. (Caecias is half north and half east.) South are that which blows from due south and Lips. East, the wind from the rising of the sun at the equinox and Eurus. Phoenicias is half south and half east. West, the wind from the true west and that called Argestes. More generally these winds are classified as northerly or southerly. The west winds are counted as northerly, for they blow from the place of sunset and are therefore colder; the east winds as southerly, for they are warmer because they blow from the place of sunrise. So the distinction of cold and hot or warm is the basis for the division of the winds into northerly and southerly. East winds are warmer than west winds because the sun shines on the east longer, whereas it leaves the west sooner and reaches it later.
205. After the Philosopher has discussed the motion of the winds and the causes of their motion, here he determines their position, their contrariety, and their other passions or affections.
And first, he lays down his intention, saying that after the aforementioned determination, he must explain the position (363a21), that is, the place and order, of the winds themselves; and their contrariety, namely, which winds are contrary to each other; and which can blow together and which cannot. It must also be considered what are the winds, according to the account of their names, and how many are the winds, according to their number. But further, he must explain their passions and accidents, or their affections, which happen to be considered in particular Problems. (The authenticity of the Problemata is disputed; see Problems, bk. 26, 940a17–947b9.) And he must show this order from the description of each, by describing each wind.
206. Second, at for clarity's sake (363a26; [206]), he pursues his intent. And concerning this, he does three things.
First, he shows the position and order of the winds.
Second, he explains their contrariety, at then since those things (363b8; [209]).
Third, he explains their accidents or affections, at since this is the distribution (364a27; [214]).
The first point, again, is in two parts.
First, he lays down certain things necessary for showing what he proposed.
Second, he concludes to what is proposed, at let A be the point [363a34; 208]).
Concerning the first point, he does two things.
First, he lays down a certain prerequisite necessary for showing the position of the winds.
Second, he lays down a certain point that is necssary for declaring their contrariety, at let us also begin (363a30; [207]).
He speak first, therefore, of that from which it is suitable to show the order of the winds, that is, from a description, as the more manifest ought to be spoken of first: in the description, the horizon is described, for the horizon is a certain circle, because of which it is also round, cutting the heavens into two hemispheres, and consequently, setting the boundaries of our sight around the earth, because it divides the hemisphere, that is, the part of heaven seen by us, from the part that is not seen by us.
But it ought to be considered that the horizons are many and diverse according to the different habitable parts of the earth. For the same horizon does not exist for those living here in Paris as for those in Rome. For since the earth in Paris is lower down and the earth in Rome is higher up, from the fact that the whole earth is round, those who live in Paris do not see the same part of the sky as those who live in Rome, for the earth, which is higher in Rome, occupies one part of their sight; but nevertheless, in both places, they can describe the following order of the wind.
207. Then, when he says, let us also begin (363a30), he lays down a certain point that is necessary for showing which winds are contraries. And he says that first we ought to suppose that contraries according to place are the furthest apart according to place, as contraries in species, that is, in form, are said to be furthest apart in form. For contraries are what are furthest apart in the same genus, and so on. (Aristotle, Categories 6, 6a15.) Nevertheless, it must not be understood from this that contraries in form are properly "apart," that is, distant in place; and therefore, they are said to be the furthest apart because they are naturally the most unlike. But those are furthest apart in place which are apart according to a diameter, that is, which are the extremes of one diametrical straight line, contraposed to each other, as is that distance of the straight line that crosses through the center of the horizon.
208. Then, when he says, let A be the point (363a34), he concludes with what he proposed, distinguishing horizons according to different points in relation to the rising and setting sun above them. And he says, in order to make the proposition more evident, that the aforementioned circle of the horizon should be described and a line be drawn through its center from east to west, which is called the equinoctial, and in one part of it, namely, in the point in the west, let the letter A be marked down, and in the other part, namely, in the point opposite to the west, that is, in the east, let the letter B be marked down. Then let another diameter be drawn, that is, another straight line, crossing through the center of the horizon and dividing the aforementioned equinoctial line at right angles, at the top of which will be the Bear, that is the north pole, and let the south, that is the south pole, be at the other head. (Septentrio can simply mean "north," but it is also a Latin name for the north wind; the name is derived from the seven (septem) stars in Ursa Minor. Similiarly, meridies, "midday," can also simply mean "south," since, in the northern hemisphere, the sun is due south at midday.)
Therefore, at the point in the south let C be put down and D at the point in the north. Again, for the part that is the rising in the summer, that is, for the northern side of the eastern part (which he calls the rising in the summer because when the sun is in that northern part of the east, it causes summer), let it be signified by the letter H. But, the letter G is assigned for the other side of the east (which is called the rising in the winter for the same reason, for when the sun is in that part, namely the southern part, it causes winter). Likewise, for the western part, the letter F is assigned for the northen part that is the setting in the summer, and the letter E is assigned for the southern part that is the setting in the winter. Again, on the southern side, the letter I is marked for the eastern part of the south, and the letter K for the western part. And likewise for the northern part: the letter L marks the eastern part of the north, and the letter M marks the western part. And the winds are disposed according to this order, as appears in the following figure.
{figure}
209. Then, when he says, then since those things (363b8), he shows which winds are the contraries of each other. And concerning this, he does two things.
First, he shows which are contraries.
Second, in order to be better understood, he determines their names, at the names of the winds (363b11; [210]).
He says first, therefore, that since those that are contraries according to place are the furthest apart according to place, but those that are furthest part according to place are at the extreme opposites of a straight line, as was said above, it follows that those winds are contraries which are apart according to the diametrical straight line that passes through the center of the horizon.
It should be known, however, that winds have a twofold contrariety with each other: one of which is contariety according to place and about which Aristotle speaks here, but another of which is contariety according to active and passive qualities, which is addressed not according to the contariety of only one quality, but according to the contrariety of both. And according to this contrariety, Subsolanus, (Etymologically, Subsolanus signifies "under the sun." The Greek word Apeliotes (ἀφηλιώτης) also signifes "from the sun.") which arises in point B and is hot and dry, is contrary to the wind Favonius, (Zephyrus (ζέφυρος) is the Greek name for this wind, perhaps derived from the Greek word for "darkness" (ζόφος), since it arises from the place of the setting sun. The name Favonius may simply be derived from favere, "to favor," although Isidore of Seville derives the etymology of Favonius from fovere, "to keep warm, to cherish, to support" (see Isidore of Seville, Etymologies, bk. 13, c. 11, para. 8). Zephyrus, the west wind, is often featured in western literature as the wind that announces the coming of spring; as in, for example, the prologue of Chaucer's Canterbury Tales.) which arises in the west at point A and is cold and wet. But Auster, (Isidore derives the name Auster from [h]auriendo aquas, "drawing waters" (Etymologies 13.11.6). The Greek name is Notus or Notos (Νότος), perhaps from νότιος, meaning "moist.") which arises from point C in the south, is hot and wet, and it is contrary to Septentrio which arises from the north under the point D of Aquilo, (Aquilo is traditionally the north-northeast wind rather than the north wind, and its inclusion in this passage here is confusing; perhaps it is mentioned here because Aristotle offers Boreas as an alternative name for Aparctias; Boreas and Aquilo were often listed as equivalent names for the north-northeast wind, although here Aristotle clearly intends the name Boreas to be an alternative name for the north wind proper. Aquilo may be etymologically derived from aquilus, "dark-colored"; as for the Greek Boreas (βορέας), there are multiple theories for its derivation, one of which is that this northerly wind in Greece came from over the mountains (ὅρος).) and which is cold and dry. Likewise, Caecias, (The commentary here mistakenly lists Vulturnus in place of Caecias; this is an oft-repeated case of mistaken naming, found in Isidore of Seville and elsewhere. The Greek Caecias (καικίας) is named from a river in Asia Minor, and thus, northeast from the perspective of the Greeks.) which arises from point H and is mildly warm and exceedingly dry (because its heat is diminished due to its proximity to the north and its dryness is increased for the same reason) is the contrary wind to Africus, (Africus, naturally, is derived from the name for Africa; the Greek equivalent is Lips (λίψ), "from Libya," to the southwest of Greece.) which arises under point E, and is mildly cool and exceedingly wet (because its coldness is diminished due to its proximity to the south and its wetness is increased for the same reason). Eurus, (The Greek name Eurus (εὖρος) is derived from the Greek ἠώς, "dawn; light of day." Vulturnus, sometimes confused for Caecias, is the Latin equivalent, perhaps named from the hills of Volturno, southeast of Rome; other etymologies trace the name to vellere, "to demolish.") which arises under point G and is exceedingly hot but moderately dry (because of its nearness to the south, its heat is increased and its dryness diminished), is the contrary wind of Corus, (Alternatively, Caurus. Isidore relates the name to a chorus, a circle of dancers, enclosing off the circle of winds (Etymologies 13.11.10), but the origin of the name remains obscure. The Greek equivalent is Argestes (ἀργέστης), "clearing; brightening," since this wind sweeps away the clouds; note, however, that Corus is also known for bringing the clouds (see, for example: Boethius, The Consolation of Philosophy, bk. 1, poem 3).) which arises at point F and is exceedingly cold and moderately wet (its coldness is increased and its wetness is diminished by being in the vicinity of the north).
And for the same reason, Austroafricus (The name Austerafricus is compounded of Auster and Africus; its Greek equivalent is Libonotus (λιβόνοτος), a word similarly compounded from Lips and Notos.) is moderately hot and exceedingly wet, and it is the wind contrary to Aquilo, which is moderately cold and exceedingly dry. So, too, Euroauster (The name Euroauster is compounded from Eurus and Auster and is thus the southeast wind; the Greek equivalent is Euronotos (εὐρόνοτος), similarly compounded.) is contrary to Circius, (Circius is a violent northwest wind; its etymology perhaps suggests circular, vortex-like motion, though Isidore relates its name to the circle of winds again, saying that it is so-called because it is joined to Corus (Etymologies 13.11.12). The Greek equivalent is Thrascias (θρασκίας), signifying the wind coming from Thrace (which historically covered an area of land that was to the northwest of Greece as well).) because, for the same reason, that wind is exceedingly hot and moderately wet, while Euroauster is moderately cold and exceedingly dry. So therefore all these winds are completely contrary for this twofold reason, namely, because they blow from opposite places according to a straight line and because they have contrary qualities. But it should also be known that since, in every wind, dry evaporation is mixed with wet (although in these winds, the dry evaporation is predominant, as was said above), the winds will exceed more or less in the aforementioned qualities according to the different proportions of the mixture of these qualities, which nevertheless also increase in these winds because of the places in which they arise and through which they travel.
210. Then, when he says, the names of the winds (363b11), he determines the names of the winds, from which it will appear more determinately which winds are contraries to which. And he says that the winds are names according to the position of the places from which they blow. For the wind is called Zephyrus that arises from A, namely, from the equinoctial east; and its contrary, which lies across from it along the diameter and blows from the equinoctial east under point B, is called Apeliotes. But the first is called Favonius by the Latins, and the second is called Subsolanus. But Boreas, which blows from D where the Bear is (that is, from the north pole), is called Aparctias, (The Greek ἀπαρκτίας signifies "from the Bear.") but by us is called Septentrio. But the wind contrary to this, which blows from C, which is the southern point, is called Auster, but by th the Greeks is called by a different name, Notus. But from G, which is the winter rising, blows Eurus. But the wind contrary to it is not that which blows from the winter setting but that which blows from the summer setting, which is opposite to it in a straight line, and is called Corus or Argestes or Olympius or Sciron. But from the winter setting, under point E, blows the wind that is called by us Africanus, or Lips, and its contrary wind is that which arises under point H, from the summer rising, and is is called Caecias or another name.
211. Then, when he says, there are other winds (363b28), he determines the contrariety of the less principal winds. And he says that there are other winds that are less principal and manifest in that region, and the other winds contrary to them are not manifest to us. Such is Thrascias, which blows from point M and divides Argestes and Aparctias and is called Circius by us. And likewise Meses, called Aquilo by us, which arises in point L and is between Caecias and Aparctias (that is, between Caecias (Again, Vulturnus is improperly placed here in the Latin, as that name usually signifies the southeast wind.) and Septentrio). But no wind that we can feel appears to blow from the opposite points, namely, from I and from K; or, if they do blow, they are weak and of short duration and do not affect us—as is that wind which is called "Phoenicias" by the inhabitants of the place, but by us is called Euroauster, and as is that wind which is called Austroafricus, for they are breezes of short duration and are thus are unnoticed by us. But Aristotle says that the aforementiond winds do not have contraries, because contrariety is principally among the four principal winds, but among the others there is no contrariety unless by participation, because the mean participates the nature of the extremes.
212. Then, when he says, there are more winds (364a5), because Aristotle had supposed above that more winds blow from the northern part than from the southern part, therefpre, he here shows the reason for this. And he says that the reason why from the north, that is, from Septentrio, between the north pole and the east, more winds blow than from the opposite part, namely, from the south, is because our habitable part is nearer to this part than to that part, and therefore the winds that come to be there are felt more by us than the others that blow from the opposite part.
Then he gives another reason by simply showing why more winds are generated here than there (for the above reason showed this only with respect to us). And the reason is that there is more water and snow there, because of the withdrawal of the sun, than there is in the other part, which lies under the sun and its course, which therefore does not let the water there freeze. For although wind is generated from dry evaporation, nevertheless, the dry evaporation cannot join or compact in the wind without moisture joining the parts of the dry evaporation and thus making more winds.
213. Then, when he says, of the winds we have described (364a13), he makes more evident what he said before: which are the northern winds and which are the southern. And he says that the northern winds are those they are also called sometimes Aparctias and Thrascias (that is, Septentrio and Circius), which are between Argestes (that is, Corus) and Boreas. But the southern winds are Auster (which is also called Ithagenes) and Lips, which winds blow from the south. But the eastern winds are Apeliotes and the rest. And, generally, the eastern winds are the two which are nearer to the east and that third one which is in between and common to both and arises in the eastern point. Thus, the western winds are those nearer to the west and that wind common to them both that arises in the western point. But the southern winds are nearer to the south, which is in between them; and the northern winds are those nearer to the north, which is in between them, as is clear from the circle that was laid down. But it must be noted that Aristotle sometimes names (and sometimes says what is called by others) one wind by the name of another, for the reason that, because of the great proximity that a place in which one arises has to the place of another, one seem to participate in the nature and name of another, as Septentrio is called Boreas, and so for each.
Then he shows why, in an extended sense, all the winds are called northern (Boreales) or southern (Australes), and he takes his argument from the similarity of their qualities. For the western winds, which are called Zephyri, are connected to the northern ones because they are colder; but the eastern winds, because they are warmer, are joined to the southern ones,; and therefore, because of the likeness of these qualities, the eastern are called southern, but the western are called northern; and thus, all winds are called northern or southern.
But he gives the reason why the southern winds are warmer, namely, because for longer, that is, for a longer time, they stand under the sun. And the northern winds are colder for the opposite reason, because they stand under the sun less. He is also able to provide another reason, namely, because the southern winds pass through hotter places and are therefore continuously made more hot, but the northern winds pass through colder regiions and are therefore always made colder.
Lecture 12
On certain effects and accidents of the winds
Since this is the distribution of the winds, it is clear that contrary winds cannot blow simultaneously. They are diametrically opposite to one another and one of the two must be overpowered and cease. Winds that are not diametrically opposite to one another may blow simultaneously: for instance the winds from H and from G. Hence it sometimes happens that both of them, though different winds and blowing from different quarters, are favourable to sailors making for the same point. Contrary winds commonly blow at opposite seasons. Thus Caecias and in general the winds north of the summer solstice blow about the time of the spring equinox, but about the autumn equinox, Lips; and Zephyrus about the summer solstice, but about the winter solstice Eurus.
The winds that fall on others most and stop them are Aparctias, Thrascias, and Argestes. Their source is so close to us that they are greater and stronger than other winds. They bring fair weather most of all winds for the same reason, for, blowing as they do, from close at hand, they overpower the other winds and stop them; they also blow away the clouds that are forming and leave a clear sky—unless they happen to be very cold. Then they do not bring fair weather, but being colder than they are strong they condense the clouds before driving them away. Caecias does not bring fair weather because it returns upon itself. Hence the saying: 'Bringing it on himself as Caecias does clouds.'
When they cease, winds are succeeded in turn by their neighbors in the direction of the movement of the sun. For an effect is most apt to be produced in the neighborhood of its cause, and the cause of winds moves with the sun.
Contrary winds have either the same or contrary effects. Thus Lips and Caecias, sometimes called Hellespontias, are both rainy, but Argestes and Eurus are dry: the latter being dry at first and rainy afterwards.
Meses and Aparctias are extremely cold and bring most snow. Aparctias, Thrascias, and Argestes bring hail. Notus, Zephyrus, and Eurus are hot. Caecias covers the sky with heavy clouds, Lips with lighter ones. Caecias does this because it returns upon itself and combines the qualities of Boreas and Eurus. By being cold it condenses and gathers the vaporous air, and because it is easterly it carries with it and drives before it a great quantity of such matter. Aparctias, Thrascias, and Argestes bring fair weather for the reason we have explained before. These winds and Meses are most commonly accompanied by lightning. They are cold because they blow from the nearby north, and lightning is due to cold, being ejected when the clouds contract. Some of these same bring hail with them for the same reason, namely, that they cause a sudden condensation.
Hurricanes are commonest in autumn, and next in spring: Aparctias, Thrascias, and Argestes give rise to them most. This is because hurricanes are generally formed when some winds are blowing and others fall on them; and these are the winds which are most apt to fall on others that are blowing, the reason for which, too, we have explained before. But the Etesiae veer round: they begin from the north, and become, for dwellers in the west, Thrasciae, Argestae, and Zephyrus (for Zephyrus belongs to the north). For dwellers in the east, they veer round as far as Apeliotes. So much for the winds, their origin and nature and the properties common to them all or peculiar to each.
214. Then, when he says, since this is the distribution (364a27), he determines those things things that are consequences of the winds. And concerning this, he does two things.
First, he discusses certain accidents of the winds.
Second, he discusses their effects, at contrary winds (364b17; [217]).
In regard to the first, he does three things.
First, he shows which winds can blow together and which cannot.
Second, he discusses the falling of winds upon each other, at the winds that fall on others (364b3; [215]).
Third, he discusses their turning around in a circle, at when they cease (364b14; [216]).
He says first, therefore, that if winds are so disposed as has already been laid down, namely, that contrary winds are placed oppositely in a straight line, then it is clear that contary winds cannot blow together. For since one would blow against the other, either both would be equally strong, and thus mutually impede each other, or one of them would be stronger and thus eliminate the weaker wind. But those which are not contrary can sometimes blow together, as, for example, G and E, that is, Eurus and Africus, sometimes blow together and to the same part, but not altogether from the same point, because Eurus blows from G and Africus from E. Neither do they also blow with the same breath, that is, with an equal force of blowing, but one is stronger and the other weaker, according to the diversity of the matter and of the contrary wind pushing back. The contrary winds, however, do not blow together, but according to different and contrary times, for contraries are the causes of contraries, and different times are contraries according to contrary qualtites. As, for example, Caecias, blowing from the point of the summer rising, frequently blows around the time of the spring equinox and generally blows until the summer solstice, when the sun is stronger. But Lips blows around the time of the fall equinox, when the sun is withdrawing from the aforementioned solstice; Zephyrus, however, blowing from the point of the western equinox, blows arounds the summer solstice or the turning around of the sun, but Eurus and Apeliotes blow around the time of the winter solstice.
215. Then, when he says, the winds that fall on others (364b3), he determines what follows from winds falling upon each other. But it is said that one wind falls upon another because, in blowing against the other, it causes it to cease. He says, therefore, that Aparctias, Thascias, and Argestes, which are called the nothern winds (Boreales), are the ones that chiefly fall upon the others and cause them to cease. And the reason for this is that the blowing of these winds is nearer to us, who live in the north, and also because the blowing of theses same winds is strong, because in the place where such winds arise, there is plenty of matter, that is, matter from which the dry evaporation comes to be. Hence, these winds easily push back the weaker winds on which they fall and thus frequently cause them to cease. They are also the causes of calmness in the air, for because of the violence of their blowing, they drive the clouds meeting them to a standstill. But this happens when they are not exceedingly cold, for then they do not calm the air but by their coldness they thicken and enlarge the vapor in the cloud, as, for example, Caecius often gathers clouds together and is not altogether calm because it does not blow completely laterally around the earth but inclines down as against the earth, and when it is turned back from the earth, then it drives the clouds it meets to its own place from which it began to blow and gathers them together there, and for this reason it is the cause of clouds and rain. Hence, it is said in a proverb about the miser that he draws money to himself as Caecias draws clouds to itself.
216. Then, when he says, when they cease (364b14), he explains the turning around of the winds in a circle. And he calls the generation of a neighboring wind a "gyration" or a "turning around in a circle," that is, going around the horizon after the cessation of the first. As, for example, when, after Subsolanus stops blowing, Eurus, which is its neighbor, comes to be, then this is called a gyration of the winds, because it comes to be according to a certain turning around a circle. Therefore, he says that when they cease, winds are succeeded in turn by their neighbors, that is, the gyrations are the generation of the following winds that are its neighbors, that is, being related consequently to the preceding ones, they come to be according to the movement of the sun. For the sun, by approaching different places, raises the dry evaporation that is the principle of the winds and thus makes winds come to be in them, but, by the sun receding, because the raising of material subsides, it causes the winds to cease. And because the sun approaches and recedes according to a certain turning around in a circle, it therefore makes "gyrationes" in turn, that is, the coming to be of winds in a circle. Therefore, because the sun first raises evaporations at the summer solstice, then at the fall equinox, afterwards at the winter solstice, and then at the spring equinox, (The Latin reads solstitio autumnali and solstitio vernali, but there is no solstice at these times.) so also, consequently, the winds are related proportionally and similarly.
217. Then, when he says, contrary winds (364b17), he determines the effects of the winds. And concerning this, he does two things.
First, he determines their primary effects.
Second, he determines their secondary effects, at Meses and Aparctias (364b21; [218]).
He says first, therefore, that contrary winds sometimes make the same thing and sometimes the contrary thing: they make the same thing in an accidental way and the contrary things through themselves (per se), since the per se effects of contaries are contraries. As, through itself, Boreas cools, but it warms accidentally, namely, by the concentration of heat: for in cooling, it collects the heat, concentrating it into some one part, and thus it warms, as was said above about the depths of the earth in winter. But Lips and Caecias bring moisture. Eurus (which because of its proximity to the eastern wind, some call Apeliotes) and Argestes, however, both bring dryness, but, nevertheless, Eurus in the end makes it rainy because of the mixing together of humid vapor.
218. Then, when he says, Meses and Aparctias (364b21), he treats their secondary effects. And he says that Aparctias and Meses produce clouds because they are extremely cold: for what is cold gathers vapor together and compacts it in a cloud. But accidentally, because of the strength of the winds, they clear up the sky be propelling the clouds to the opposite part. But those winds that frequently bring about hail are the same Aparctias (that is, Boreas), Thrascias, and Argestes, because their extreme cold causes freezing. And the winds that cause heat are Auster, Zephyrus, and Eurus, either because of the heat of the raised evaporation itself or because of the heat of the place through which they are borne. But that which is said here about the heat of the southern winds, because of the heat of the place through which they travel, is true also about the northern winds, for as Auster is hot because of the heat of its place, so also, Boreas, its contrary, is cold because of the coldness of the place in which it arises and through which it travels: for in nature the contraries are always causes of contrary effects. But Caecias greatly compacts the sky, that is, the air, with clouds, and Lips, its contrary, make the sky lighter; this is because Caecias, bent back, propels clouds to its own place in which it arose from the start, and it is also cold, and besides this, it has much matter that it propels, because it is easterly, that is, it is near the wind Apeliotes, where the sun raises much evaporation. And Aparctias, Thrascias, and Argestes clear up the sky for the aforementioned reason, namely, accidentally, because of the strength of these winds. And these same winds, and likewise Meses, make lightning because they are cold and blow from the nearby northern parts, which are cold. For lightning and thunder come to be from the cold, for, in becoming cold, clouds expel the dry evaporation, enclosed and partly enkindled in them, and force it to leave. And for the same reason, certain of these make hail, because by their coldness, they quickly freeze the cloud into hail.
219. Then, when he says, hurricanes are commonest (365a1), he shows which winds make hurricanes more. But it should be known that "hurricane" can be taken in two senses. In one sense, and chiefly, inasmuch as a hurrican is a certain breeze blowing from the clouds toward the earth with violence, and in regard to this sense of the word, he will discuss it in the third book. But, in another sense, the word is taken to mean the motion above or below each wind, because of the violence of another wind falling upon it, and it is in this way that it is discussed here. He says, therefore, that hurricanes happen mostly in the fall, and next most often in the spring. And Aparctias, Thrascias, and Argestes mostly make those winds because hurricanes mostly happen when some winds fall upon others, propelling them to the earth because of the violence of the blowing, as was said; but the ones that do this are the aforementioned winds, which blow intensely and are the winds that chiefly fall upon others, as was said above. But the etesiae, that is, annual winds, blow in gyrations according to a circle: for those living in the west, they begin from Boreas and then proceed into Thrascias and into Argestes and are brought to an end in Zephyrus, which is cold. But in the east, they become gyrations from the same Boreas and blow towards the west and south until they reach Apeliotes, which blows from the equinoctial east.
Then he recapitulates what was said, saying that so much has been said about the winds, namely, about their substance, generation, movement, and furthermore, about their common accidents and the properties of each one of them.
Resumption of Commentary by Thomas Aquinas
Lecture 13
Refutation of certain opinions on earthquakes
We must go on to discuss earthquakes next, for their cause is akin to our last subject.
The theories that have been handed down up to the present date are three, and their authors, three men, Anaxagoras of Clazomenae, and before him, Anaximenes of Miletus, and later, Democritus of Abdera.
Anaxagoras says that the ether, which naturally moves upwards, is caught in hollows below the earth and so shakes it, for though the earth is really all of it equally porous, its surface is clogged up due to the rain. This implies that part of the whole sphere is 'above' and part 'below': 'above' being the part on which we live, 'below' the other.
This theory is perhaps too primitive to require saying anything to refute it. For it is stupid to think of up and down as being so and not as meaning that heavy bodies move to the earth from every quarter, and light ones, such as fire, move up from it;
And this we see especially from the fact that, as far as our knowledge of the earth goes, the horizon always changes with a change in our position, which proves that the earth is convex and spherical.
It is absurd, too, to maintain that the earth rests on the air because of its size, and then to say that impact upwards from below shakes it right through.
Besides, he gives no account of the circumstances attendant on earthquakes: for not every country or every season is subject to them.
Democritus says that the earth is full of water and that when a quantity of rain-water is added to this an earthquake is the result. For the bowels of the earth being unable to admit the excess of water, it forces its way in and so causes an earthquake. Or again, the earth as it dries draws the water from the fuller to the emptier parts, and the inrush of the water as it changes its place causes the earthquake.
Anaximenes says that the earth breaks up when it grows wet or dry, and earthquakes are due to the fall of these masses as they break away. Hence earthquakes take place in times of drought and again of heavy rain, since, as we have explained, the earth grows dry in time of drought and breaks up, whereas the rain makes it sodden and sink down.
But if this were the case the earth ought to be found to be sinking in many places.
Again, why do earthquakes frequently occur in places which are not excessively subject to drought or rain as are others, as they ought to be on the theory?
Besides, on this view, earthquakes ought always to be getting fewer and should come to an end entirely some day: the notion of contraction by packing together implies this. So if this is impossible, it is clear that it must be impossible also for this to be the cause.
220. We must go on to discuss earthquakes next (365a14). After the Philosopher has discussed the winds blowing in the air, here, he discusses the effects of the winds.
And first, he treats earthquakes, which are caused by wind coming to be below the ground.
Second, he treats thunder, which is caused by wind in the clouds, at let us go on to explain lightning and thunder (368b10; [243])
Concerning the first, he does two things.
First, he says what his intention is about. And he says that next after the winds we must go on to discuss earthquakes. And he gives as the reason for the order that their cause, that is, the cause of earthquakes, is akin, that is, follows also the preceding last subject of the winds: for that which causes wind in air is this that cases the shaking of the earth below the ground. (Cf. Alexander of Aphrodisias, Commentaire sur les Météores d’Aristote, ed. A. J. Smet, Corpus latinum commentariorum in Aristotelem graecorum 4 (Louvain and Paris, 1968), 180.9–14.)
221. Second, when he says, the theories that have been handed down (365a15), he pursues his proposition.
And first, he pursues it according the opinion of others.
Second, he pursues it according to the truth, at we have already shown (365b21; [226]).
Concerning the first, he does two things.
First, he enumerates the opinions and those opining. And he says that there were three opinions up to his own present date about earthquakes coming from three philosphers, of whom one was Anaxagoras, another was his predecessor Anaximenes, who also was said to have been Anaxagoras's teacher, and third, after them was Democritus; and he names them from the places from which they came.
Second, at Anaxagoras says that the ether (365a19), he pursues the opinions.
And first, he pursues the opinion of Anaxagoras
Second, he pursues the opinion of Democritus, at Democritus says (365b1; [223])
Third, he pursues the opinion of Anaximenes, at Anaximenes says (365b6; [224])
Concerning the first, he does two things.
First, he provides the opinion. About which it must be known that Anaxagoras thought that "above" and "below" were distinguished in the world from the position of man, as, namely, whatever is in the world above our head is "above," and whatever is completely towards our feet is "below"; and from this it follows that as the earth is lower than one part of the heavenly sphere, so too is it higher with respect to the opposite part.
Therefore, because ether, which Anaxagoras called the fire out of which he proposed the whole heavens consisted, is naturally borne upwards, but the earth is up with respect to the other part of heaven, it follows that the ether is naturally borne towards the earth from below. And so he said that it falls into hollows which are in the lower part of the earth, and thus the ether, enclosed inside the earth, moves it. For he said that the whole earth is naturally porous, (Gk. σομφή.) that is, hollow and spongy, but this porousness does not appear in the upper part of the earth, since the upper parts of the earth are closed up and are not hollow due to the rain making the earth wet. For it is obvious that because dryness makes fissures and hollows in the ground, it follows that hollows of this sort are prevented by the rain. And this very thing was said by Anaxagoras, just as if one part of the whole world sphere is lower, that which is towards our feet, and the other part is higher, namely, the part on which we live.
222. Second, at this theory is perhaps too primitive (365a25), he disproves this opinion with four arguments.
In the first of these arguments, he says that since this reason is primitive and is given unreasonably, there would not be much use in him saying anything against it, for the reason that the theory clearly does not fittingly hold together. For it is stupid to think that up and down are determined so in the world—the contrary of which position he himself proposes—insofar as down is not said in respect to the place of the earth in the whole world to which heavy bodies are carried, and up is not said to be the opposite place to which light bodies are carried.
He gives the second reason at and this we see especially (365a29). In order to understand this reason, one should consider that Anaxagoras proposed that fire was naturally borne to earth from the other part of the sphere just as if it were forced up, and for the same reason he proposed that the whole earth naturally tended towards heaven as if this were down. But he said this was prevented by the width of the earth, and hence, he did not think the earth was spherical in shape but extended, as if it were floating in the air in the same manner in which extended bodies float in water but round bodies sink.
But to say this is stupid, since we see, as far as our knowledge goes, in the whole earth, when we go from one place to another, the horizon is always changed, because a small change in position is either more or less raised above the horizon, and this would not be if the earth were extended in figure or curved inward, and through this it is shown that the earth is spherical in shape and convex for our part.
He provides the third reason at it is absurd, too (365a31) And he says that it is also stupid to maintain that the earth rests on the air because of its own size, and that nevertheless is completely shaken by the ether striking upwards against it as if from below. For these seem to be contraries, namely, that it rests and that is moved.
He gives the fourth reason at besides, he gives no account (365a33). And he says that by this cause, which they give for the earthquake, no reason is able to be given for those accidents that are attendant on earthquakes, for neither every country nor every season is subject to them, as they would be if earthquakes happened for the given reason.
223. Then, when he says, Democritus says (365b1), he gives the opinion of Democritus. And he says that Democritus claimed that the inside of the earth was full of water, but nevertheless, it is moved by a lot of additional rain-water arriving from the surface. For as the water grows, the chasms that are under the earth, which he calls its bowels, are unable to admit easily the water arriving with some violence, and from this an earthquake results. And also at the time that the water arrives it draws parts of the earth which, because of dryness are found to be accessible, and so, as long as there is as much water as earth arriving from the fuller places and pressing on the emptier parts, it causes a shaking of the earth.
But he does not refute this opinion in particular, both because his refutation is apparent from those things he has already said about the coming to be of rivers and fountains and also because of how much some of it agrees with the following opinion.
224. Then, when he says, Anaximenes says (365b6), he gives the opinion of Anaximenes. And concerning this, he does two things.
First, he relates the opinion. And he says that Anaximenes claimed that the earth becomes dry after it is rained upon and breaks up so that certain openings appear, and due to these openings, things fall below to no purpose, from which the earth is shaken. And he took as a sign of this the fact that earthquakes happen as much in times of drought as in times of rain. Indeed, they happen in drought because the earth is broken apart by the drying up, and they happen when it is rainy because the water making the earth wet causes the earth to sink down below; and this much of the theory is also in agreement with Democritus.
225. Second, at but if this were the case (365b12), he disproves the aforementioned opinion in three ways.
First, indeed, because if an earthquake were to happen for this reason, the overturning of the earth ought to appear in many places due to parts of the earth having sunk down below in prior earthquakes.
Second, at again, why do earthquakes (365b13), he disproves the opinion from the fact that earthquakes frequently occur in certain places in which, nonetheless, there does not appear an excess of such breaking apart through their being different from other places, which nevertheless ought to be so if what was said is the cause of earthquakes, because the multiplication of effects occurs from the multiplication of the cause.
Third, at besides, on this view (365b16), he disproves the opinion from the fact that earthquakes ought always to be getting fewer and fewer, and should altogether cease to be some day, for if the higher parts sink below, it should be the case that sometimes the parts below are filled so that they cannot sink any further. Hence, if this is impossible, it is also impossible for this which was said to be the cause of earthquakes.
Lecture 14
Origin of earthquakes according to Aristotle
We have already shown that wet and dry must both give rise to an evaporation: earthquakes are a necessary consequence of this fact.
The earth is essentially dry, but rain fills it with much moisture, while then the sun and the earth's own fire warm it and give rise to a quantity of wind both outside and inside it. This wind sometimes flows outwards in a single body, sometimes inwards, and sometimes it is divided.
If, therefore, it is impossible for this to be otherwise, we must next find out what body has the greatest motive force. This will certainly be the body that naturally goes to the greatest amount and which is the most violent. Now that which has the most rapid motion is necessarily the most violent; for its swiftness gives its impact the greatest force. Again, the rarest body, that which can most readily pass through every other body, is that which naturally moves to the greatest amount. Wind satisfies these conditions in the highest degree (fire only becomes flame and moves rapidly when wind accompanies it):
so that not water nor earth is the cause of earthquakes but wind—that is, the inrush of the external evaporation into the earth.
Hence, since the evaporation generally follows in a continuous body in the direction in which it first started, and either all of it flows inwards or all outwards, most earthquakes and the greatest are accompanied by calm.
It is true that some take place when a wind is blowing, but this presents no difficulty. We sometimes find several winds blowing simultaneously. If one of these enters the earth we get an earthquake attended by wind. Only these earthquakes are less severe because their source and cause is divided.
Again, most earthquakes and the severest occur at night or, if they occur during the day, about noon, that being generally the calmest part of the day. For when the sun fully prevails (as it does about noon) it shuts the evaporation into the earth. Night, too, is calmer than day because the absence of the sun makes the evaporation return into the earth like a sort of ebb tide, corresponding to the outward flow, especially towards dawn, for the winds, as a rule, begin to blow then. If, therefore, their source changes about like the Euripus and flows inwards the quantity of wind in the earth is greater and a more violent earthquake results.
The severest earthquakes happen around those places where the sea is full of currents or the earth spongy and cavernous: so they occur near the Hellespont and in Achaea and Sicily, and those parts of Euboea which correspond to our description—where the sea is seen to flow in channels below the earth. The hot springs, too, near Aedepsus are due to a cause of this kind. It is the confined character of these places that makes them so liable to earthquakes. A great and therefore violent wind is developed, which would naturally blow away from the earth: but the onrush of the sea in a great mass thrusts it back into the earth. The countries that are hollow below the surface are exposed to earthquakes because they have room for so much wind.
For the same reason, earthquakes usually take place in spring and autumn and in times of wet and of drought—because these are the windiest seasons. Summer because of its heat and winter because of its frost cause calm: winter is too cold, summer too dry for winds to form. In time of drought the air is full of wind; for drought is when there is more of the dry than moist evaporation. Again, excessive rain causes more of the evaporation to form in the earth. Then this secretion is shut up in narrow places and forced into a smaller space by the water that fills the cavities. Thus a great wind is compressed into a smaller space and so when it begins to get the upper hand, it then breaks out and beats against the earth and shakes it violently.
We must suppose the action of the wind in the earth to be analogous to the tremors and throbbings caused in us by the force of the wind contained in our bodies. Thus some earthquakes are a sort of tremor, others a sort of throbbing. Again, we must think of an earthquake as something like the tremor that often runs through the body after urinating as the wind suddenly returns inwards from without in one volume; for such things also happen in regard to the earth.
But the force wind can have may be gathered not only from what happens in the air (where one might suppose that its power to produce such effects is due to its volume), but also from what is observed in animal bodies. For spasms and cramps are motions of wind, and their force is such that the united efforts of many men do not succeed in overcoming the movements of the patients. We must suppose, then (to compare great things with small), that what happens in the earth is just like that.
Our theory has been verified by actual observation in many places. It has been known to happen that an earthquake did not cease until the wind that caused it burst through the earth into the air and appeared visibly like a hurricane. This happened lately near Heracleia in Pontus and some time past at the sacred island of Hiera, one of the group called the Aeolian islands, on which a portion of the earth swelled up and a lump like a mound rose with a noise: finally it burst, and a great wind came out of it and threw up live cinders and ashes which buried the neighboring town of Lipara and reached some of the towns in Italy.
The spot where this eruption occurred is still to be seen. Indeed, this must be recognized as the cause of the fire that is generated in the earth: the air is first broken up in small particles and then the wind is beaten about and so catches fire.
A phenomenon in these islands affords further evidence of the fact that winds move below the surface of the earth. When a south wind is going to blow there is a premonitory indication: a sound is heard in the places from which the eruptions issue. This is because the sea is being pushed on from a distance and its advance thrusts back into the earth the wind that was issuing from it. The reason why there is a noise and no quake is that the underground spaces are so extensive in proportion to the quantity of the air that is being driven on that the wind slips away into the void beyond.
Again, a sign of our theory as to the cause of earthquakes is that the sun appears hazy and is darkened in the absence of clouds, and that there is sometimes calm and sharp cold before earthquakes at sunrise. For the sun is necessarily obscured and darkened when the evaporation which dissolves and rarefies the air begins to withdraw into the earth. The calm, too, and the cold towards sunrise and dawn follow from the theory. The calm we have already explained. There must as a rule be calm because the wind flows back into the earth: and it must be most marked before the more violent earthquakes, for when the wind is not part outside earth, part inside, but moves in a single body, its strength must be greater. But the cold comes because the evaporation which is naturally and essentially hot enters the earth. (Wind is not recognized to be hot, because it sets the air in motion, and that is full of a quantity of cold vapor. It is the same with the breath we blow from our mouth: close by it is hot, as it is when we open our mouth wide, but there is so little of it that it is not apparent in the same way, whereas at a distance it is cold for the same reason as wind.) Well, when this evaporation disappears into the earth the vaporous exhalation concentrates and causes cold in any place in which this disappearance occurs.
A sign which sometimes precedes earthquakes can be explained by the same cause. Either by day or a little after sunset, in fine weather, a little, light, stretched-out and long cloud is seen, like a long very straight line. This is because the wind is leaving the air and dying down. Something analogous to this happens on the sea-shore. When the sea breaks in great waves the surf leaves marks on the shore that are very thick and crooked, but when the sea is calm they are slight and straight (because the secretion is small). As the sea is to the shore so the wind is to the cloudy air; so, when there is calm, this very straight and thin cloud is left, a sort of wave-mark in the air.
An earthquake sometimes coincides with an eclipse of the moon for the same reason. For when it is near the point of interposition, but the light and heat of the sun has not quite vanished from the air but is dying away, the wind, which causes the earthquake before the eclipse, turns off into the earth and calm ensues. For there also often are winds before eclipses: at nightfall if the eclipse is at midnight, and at midnight if the eclipse is at dawn. They are caused by the lessening of the warmth from the moon when its sphere approaches the point at which the eclipse is going to take place. So the influence which restrained and quieted the air weakens and the air moves again and a wind rises, and does so later, the later the eclipse.
226. We have already shown, etc. (365b21). After the Philosopher has rejected the opinions of others about earthquakes, he here determines them according to his own opinion.
And first, he assigns the cause of earthquakes.
Second, he gives the cause of certain accidents surround them, at a severe earthquake (367b32; [238]).
Concerning the first, he does two things.
First, he assigns the cause of eartquakes.
Second, at the earth is essentially dry (365b24), he shows that the cause is well assigned.
He says, therefore, that it was said in what has come before that there is a twofold evaporation: a steamy evaporation that is released from wet, and a smoky evaporation that is released from dry, and it is from this evaporation that an earthquake is caused.
Second, at the earth is essentially dry (365b24), he proves that the cause is well assigned.
And first, he proves this by argument.
Second, he proves it through signs, at hence, since the evaporation (366a5; [229]).
But he makes use of this sort of argument: dry evaporation causes wind; hence, when it is held beneath the ground it causes wind under the ground; but wind is what has the greatest force for moving bodies; therefore, it is reasonable for an earthquake to be caused by wind. Concerning this argument, he does three things.
First, he shows that the dry evaporation would cause wind underground. And he says that although the earth is essentially dry, nevertheless, because it receives rain, it has much moisture. While thus, first from the heat of the sun, then from the heat enclosed inside the ground, which is from the sun and stars, much smokiness is evaporated from the ground from which much of the wind is caused. And sometimes all the matter is held inside, beneath the earth and causes wind there; but sometimes it is partly kept beneath the earth partly lifted above it, and thus wind is caused in both places.
227. Second, at if, therefore, it is impossible (365b28), he shows that wind has the greatest power for moving bodies. And he says that since it is impossible for what was said before to be otherwise, one should consider what is the greatest motive force. Two things are required for this. One of which is that it can move to a great distance: for since bodily movers do not move unless they are moved, it must be that what is moved the most is able to move much. Second, it must be that it is vigorous and violent in order to impel strongly. But that something be the most violent, in order to impel violently, is fitting with that which is so from the speed of its motion, because what is borne swiftly also impacts strongly. And that something be what can go to a great distance is fitting with that which is so from its rarity, by reason of which it can penetrate through everything. But these two requirements fit with the wind, namely, the speed of its motion and its rarity; hence, it follows that wind is able to move bodies in the highest degree. And this is apparent not only through argument, but also through the senses, since when wind is added to fire, it becomes a conflagration and *moves *quickly.
228. Third, at so not water (366a3), he bring in the conclusion he principally intended, namely, that the cause of an earthquake is neither water, as Democritus said, nor earth, as Anaximenes said, but wind, when, that is, the stream of evaporation is kept beneath the earth.
229. Then, when he says, hence, since the evaporation (366a5), he shows the cause he has given through signs.
And first, he shows the cause through signs taken from the winds themselves.
Second, he shows the cause through signs taken from lower things, at the severest earthquakes (366a23; [230])
Third, he shows the cause through signs taken from things existing on high, at again, a sign of our theory (367a20; [235])
Concering the first, he does three things.
First, he provides a sign taken from the winds in general. And he says that because an earthquake happens because of wind kept beneath the earth, most earthquakes and the greatest happen when the air is calm from winds, because since the whole evaporation, which is released from the earth and is the matter of the wind, is as something one and continuous, it generally follows in the direction in which it first started; hence, if that which first evaporates is carried beneath the earth, the whole evaportation will be contained there, and thus all the winds will be below the earth causing an earthquake, and outside, there will be calm. But the converse will be the case if the source of the evaporation is carried outwards.
Second, at, it is true that some take place (366a8) he excludes a certain objection that can be brought up from the fact that sometimes earthquakes happen even when there winds do exist in the air. And he says that this presents no difficulty. For we sometimes find that even in the air ther are many winds blowing simultaneously, as is clear from above; hence, if two winds are caused, and one of these is borne beneath the earth, making an earthquake, and the other is in the air, it would follow that earthquake would occur simulataneously with the wind in the air. But, nevertheless, it would be necessary that an earthquake of this sort would be less severe because the evaporation that their source and cause would be divided, part of it flowing outside and part of it kept inside.
Third, at, again, most earthquakes (366a13), he describes that sign taken from winds in certain special cases. And he says that most earthquakes and the severest occur at night rather than in the day, but that if they occur during the day, they are more severe about noon. And he gives the reason why, of earthquakes that occur during the day, the most severe are those that happen about noon, namely, that these hours are generally the part of the day where there there is the greatest calm from the winds, because when the sun fully triumphs over the earth, it makes the evaporation that causes the winds to recede beneath the earth. For the rarefied evaporation which is then raised on high because of the triumph of the sun is consumed and dispersed. But because the sun does not have such a triumph beneath the earth, it indeed melts the evaporation but does not consume it; and hence it is that when the sun fully prevails over the earth, the evaporation is fully enclosed beneath it. Hence, when the sun fully triumphs at noon, then the evaporation fully recedes below the earth while there is calm in the air, and therefore the severest earthquakes that happen during the day happen at noon. But, in the night, they are still greater because in the night there is calm in the air (for the evaporations that cause winds are not so raised as in the day, because the absence of the sun, even if sometimes it happens that there are winds in the night because of evaporations raised before. And therefore, after the release of the evaporations caused in the day in the presence of the sun, because the cause that raises them ceases to be at night, the evaporations hasten back, corresponding to the outward flow, namely, they return beneath the earth, and therefore, the earthquakes are caused at night. And this happens especially towards dawn, because at night the evaporations are held beneath the earth as if frozen, but towards the dawn, because of the approach of the sun, the evaporations are melted and winds are raised up. Hence, if the source of the winds is found underground, it will make a more violent earthquake because the quantity of matter returning beneath the earth happens like the motion of the Euripus, which is forcefully moved because because of the water's return.
230. Then, when he says, the severest earthquakes (366a23), he shows the aforementioned cause of an earthquake through signs taken from lower things.
And first, he lays down general signs.
Second, at our theory has been verified (366b30; [233]), he lays down specific signs.
Concering the first, he does three things.
First, he gives signs taken from places.
Second, at for the same reason (366b2; [231]), he gives signs taken from the seasons.
Third, at we must suppose (366b14; [232]), he gives signs taken from our bodies.
First, therefore, he says that because earthquakes are caused from wind held beneath the ground, it follows that the most severe earthquakes happen around those places in which either the sea has a great flow or the earth is spongy and full of caverns. And he provides an example from certain places, as is seen in the Hellespont (I.e., the Dardanelles, the narrow strait dividing Europe from Asia, known for its strong currents.) and in Achaea and in Sicily and those certain parts in which the sea flows in channels below the earth because of the earth being full of caverns. And from that cause, because, namely, the earth is cavernous and the sea pushes strongly, he says it makes hot springs, that is, emanations of hot water, in a certain place. For because of the pushing that is caused from the motion of the sea beneath the earth, heat and internal fire is stirred up, and especially if there are cavernous places in which air is contained; and through burning of this sort, the earth is made sulfurous. But he says that in the aforementioned places that are near greatly flowing seas, earthquakes are caused by the narrow confining of the interior wind from the impulse of the sea not allowing it to breathe out, for the violent wind that would naturally leave away from the earth is thrust back into the earth by the onrush of the sea in a great mass which itself is driven against the earth by the external wind. He also gives the reason why earthquakes happen in cavernous places. And he says that whichever countries have cavernous places beneath the earth, which are hollow because not full with solid bodies, are exposed to the shaking of earthquakes, because they receive so much wind into caverns of this sort.
231. Then, when he says, for the same reason (366b2), he sets forth signs taken from the seasons. And he says that earthquakes usually happen in the spring and in the autumn and also in seasons of drought and of wet, for the same reason, namely, for the reason that earthquakes are caused by winds, and hence they usually happen in the spring and autumn. For in the winter, the winds are stilled because of the cold and also the frost, for cold impedes the release of the evaporations that are the matter of the winds, but in the summer, because of the tremendous heat and dryness, it is such that there is no matter on the earth from which the evaporation can be released (similarly to how only a small amount of smoke is released from very dry wood), because at that time the sun prevails over the earth the most.
But one could fashion an objection here from what was said above, namely, that the most severe earthquakes occur at noon because at that time the sun prevails over the earth the most; hence, if the sun prevails the most in the summer, it seems then that earthquakes ought to happen the most then.
But the cases are not similar, because although the triumph of the sun that happens at noon is sufficient for drying the wetness on the surface of the earth, such that the evaporations cannot be gathered together to make an evaporation of wind, nevertheless, it is not sufficient for the complete drying the earth such as happens in the summer, by which not even interior wetness is left over from which matter for the winds can be released.
He gives another reason why earthquakes happen in dry seasons, because at that time the air is windy, for there is drought, that is, air without water, when more comes from dry evaporation than from the moist, which dry evaporation is indeed the matter for the winds. But nevertheless, it must be understand that this does not happen when there is so much dryness that it consumes the wetness of the earth so as to prevent evaporation, as happens sometimes in the summer. But in seasons of excessive rain, earthquakes happen because of the great quantity of evaporation that is enclosed in narrow places beneath earth and is squeezed into a smaller place because the hollows of the earth in rainy seasons are full of water, and thus when the evaporation begins to triumph, the wind generated from it thrusts against the parts of the earth because of the compression, and it shakes it violently.
232. Then, when he says, we must suppose (366b14), he sets forth the signs that are taken from our bodies. And he says that as a tremor and throbbing happens in our bodies because of wind enclosed therein which does not have an opening free to leave from, similarly it happens with wind enclosed in the ground. Hence, some earthquakes are like a tremor and some are like a throbbing. And he says that as, after urinating, a tremor frequently runs in the body for the reason that wind from the outside suddenly enters within, passing through the place from which the urine leaves, and so it happens in regard to the earth, for the wind enclosed within makes a tremor in the earth. But that wind can have great force for moving is apparent not only from what happens in the air, where it can be said that it can cause great effects due to its own volume, but also from those things that a small amount of wind enclosed within us can cause to happen in our bodies. For it is manifest that cramps and spasms, which happen because of the contraction of nerves, are due to the motion of wind that is drawn back and, being drawn back, pulls back the nerves. And spasms of this sort have such violent motion that many men gathered together have sometimes tried to restrain them by force to prevent the nerves from contracting, and nevertheless they could not overcome the movements of the patients. And so we must suppose, then, to make a comparison of smaller things to greater, that wind enclosed within the earth moves the earth with great violence.
233. Then, when he says, our theory has been verified (366b30), he sets forth the signs taken from certain particular accidents. The first of which is that he says an earthquake has happened in some places which did not cease until the wind that was moving the earth visibly burst out of the earth in the way in which wind that is called a hurricane, which he speaks about below, comes out of a cloud. And he says that this happened in his own time in Pontus near Heracleia, (On the southern coast of the Black Sea.) and he says this happened some time past on an island sacred to Vulcan, (The Aeolian islands are located off the north coast of Sicily. The island Vulcano, historically named Thermessa (or Therasia, due to a copyist error found in Pliny, Natural History 3.14), was said in Greek mythology to be one of the foundaries of Vulcan's workship. The island is also sometimes designated by the name Hiera (Greek for "sacred") since, as Strabo says, it is now called "sacred" to Hephaistos (Gk. νῦν ἱερὰν Ἡφαίστου καλοῦσι); see Strabo, Geography 6.2.10. It is interesting to note that the term "Vulcanian eruption" (used in the Volcanic Explosivity Index to describe a type of volcanic eruption, characterized by noisy, ash-laden gas explosions) is itself based on the relatively recent observations of this island by the Catholic priest and volcanologist, Giuseppe Mercalli, who described the eruptions of Vulcano in 1888 as being "like cannon fire" (Ital. come cannonate i boati della Fossa di Vulcano); see Giuseppe Mercalli, I vulcani attivi della terra (Milan: Ulrico Hoepli, 1907), ch. 3, 102.) on which sometimes the earth swelled up and with a noise raised a certain lump like a mound, which finally burst because of the violence of the wind inside it, and a great wind came out from there, raising live cinders and ashes, because of which the town of Lipara was filled with ash, and that ash reached many Italian towns. And he says that traces of that event appeared even in his own time. **Indeed, this is the cause of that fire which appears on that island, or even in some other earth, because air beneath the ground is divided into small parts and is set on fire by the motion, and first the earth is kindled from such a fire, and the effect of this kindling lasts for a long time.
234. But he provides a second particular sign at a phenomenon in these islands (367a11). And he says that we can accept the argument that winds move below the surface of the earth from what happens in these islands, namely, Vulcano and the other islands called "Aeolian," because islands of this sort give a forewarning when a south wind is going to blow by some sound caused by this, that when the south wind begins to blow a little from far away and from the sea, that which ought to blow outside the earth from the wind is thrust back again into the earth because the sea falls upon it; and thus it makes a noise. Nevertheless, whenever this happens without a quake, (Gk. σεισμὸς.) that is, an earthquake, then the reason for this is sometimes that the cavernous places beneath the earth are so spacious that the internal wind enclosed therein is dispersed into the void, but also sometimes the reason is that there is a small quantity of evaporation driven back, which, whenever it is a small amount, is insufficient to cause an earthquake.
235. Then, when he says, again, a sign of our theory (367a20), he puts forth signs taken from things that happen on high. And this section is divided into three parts according to the three signs that he gives.
The second part begins at a sign which sometimes precedes earthquakes (367b7; [236]).
The third part begins at an earthquake sometimes coincides (367b19; [237]).
First, therefore, he says that one ought to take for a sign of the cause that he designated for earthquakes the fact that the sun becomes hazy and dark in the absence of any apparent clouds, and that before earthquakes that take place in the morning, there is sometimes a calm in the air and great cold. For close to an earthquake, the sun thus appears hazy and dark because the wind that could rarify the air and separate the evaporations begins to enter under the earth around the time of the earthquake. Similarly, too, before earthquakes that happen at sunrise, there is calm, because as we have explained, as a rule there is calm before an earthquake, since the wind is enclosed beneath the ground, and this happens especially around great earthquakes, because when the principle of the wind is not divided so that one part of it proceeds below ground and another part outside the ground, but is borne in a single body, then it is necessary that the strength of the wind be greater for moving either the air or the earth. But the cold comes before an earthquake for the reason that the evaporation, which is hot according to its own nature (inasmuch as it still retains something of the power of releasing heat), is not in the air but is turned back under the ground. But although the evaporation is essentially hot, nevertheless, wind is not recognized to be hot, because it stirs up the air, full of a quantity of cold vapor, which cold vapor is all the more felt through this sort of agitation, just as also with the breath we blow from our mouth, which is hot in itself and is felt to be so close by, as it is when we open our mouth wide, whereas at a distance it feels cold for the same reason, namely, because of the cold vapor that is stirred up, although our own blowing is not apparent in the same way as the wind because there is so little of it. When, therefore, such evaporation is enclosed beneath the earth at the instant of the earthquake, it is reasonable that around that place in which the earthquake happens, the wet vapors that are in the air are released and cause cold.
236. Then, when he says, a sign which sometimes precedes earthquakes (367b7), he gives another sign. And he says that this indeed, namely, wind enclosed beneath the ground and ceasing to be in the air, is the cause of what he was wont to take as a sign preceding an earthquake, because before a nocturnal earthquake, by day or after the setting of the sun, if there is clear weather, a certain little, light cloud, stretched-out in length and straight, is seen, by which it is signified that the wind in the air will have died down and be enclosed beneath the earth. For as on the shore of the sea, when a large wind has made the sea to swell with waves, the surf, (Gk. ῥηγμίν.) that is, the waviness of the sea, is very thick and crooked, but when the sea is made calm, they are slight and straight because the sea is little disturbed by the wind. So it happens in the cloudy air that when there is calm in the air, what is left is straight and thin, as such a cloud is so related to the air as the surf is to sea.
237. Then, when he says, an earthquake sometimes coincides (367b19), he gives the third sign. And he says that for the same reason, namely, the calm present in the air, an earthquake sometimes happens around the time of an eclipse of the moon, that is, the eclipse which the moon makes when it interposes itself between us and the sun, which happens in solar eclipses, because when the time is near during which the moon is interposed between us and the sun, but the light and heat of the sun has not quite vanished from the air, but is dying away, that is, is weakening, then calm ensues in the air, because since the weak heat cannot raise evaporations high, they are borne below the earth, and then the winds kept beneath the ground causes the earthquake before the eclipse. But sometimes there are also winds before lunar eclipses: at nightfall if the eclipse happens in the middle of the night, but at midnight if the eclipse happens at dawn. And they are caused because the heat which is in the air from the moon is weakened when the moon approaches the place of the eclipse. The air, however, is restrained by the power of the lunar heat, so that it is not disturbed and is quiet, for the moon has an obvious effect in the preservation of lower things (and chiefly in the preservation of wet things), and thus the air is disturbed by lessening of the lunar heat and a wind rises. And if the eclipse happens later, that is, it is even more delayed, then the wind is also harsher.
Or the passage can be explained in another way as saying also what was said above, such that an earthquake coincides with an eclipse of the moon is understood with reference to lunar eclipses. And that which he says, namely, when it is near the point of interposition, must not be understood of the interposition of the moon between us and the sun but rather of the imposition of the earth's shadow. And that which he says, namely, the light and heat of the sun has not quite vanished from the air, must be understood of the light and heat that the moon receives from the sun.
But then it seems that he saying two contrary things: for first indeed he said that before lunar eclipses happen, there is calm from the heat subsiding, but later he said that before lunar eclipsises, the diminution of its head causes the air to be distrubed.
But it can be said in response to this that the diminution of heat which is from the moon sometimes causes calm, namely, when the heat of the moon was moderate and at the same time so as to set in motion the evaporations that generate the winds, and hence, the diminution of the heat cause the winds to cease. But when the heat of the moon was greater, so as to conquer the evaporations and separate them, then the heat of the moon causes calm and the diminution of its heat causes winds.
It can also be said that just before lunar eclipses, there is calm, because of the great diminution of lunar heat; but the Philosopher does not say that winds come to be immediately before eclipses but instead in the middle of the night before, because then the heat of the moon is somewhat diminished, but has not completely died down, that is, been completely weakened.
Lecture 15
On the accidents that follow from earthquakes
A severe earthquake does not stop at once or after a single shock, but first the shocks go on, often for about forty days; after that, for one or even two years it gives premonitory indications in the same place. The reason for the severity of the earthquake is the quantity of wind and the shape of the passages through which it flows. For where it is beaten back and cannot easily find its way out, the shocks are most violent, and there it must remain in a cramped space like water that cannot escape. Just as any throbbing in the body does not cease suddenly or quickly, but by degrees according as the affection passes off, so here the principle that created the evaporation and gave it an impulse to motion clearly does not at once exhaust the whole of the material from which it forms the wind which we call an earthquake. So until the rest of this is consumed, the shocks must continue, though more gently, and they must go on until there is too little of the evaporation left to move anything perceptibly.
Underground noises, too, are due to the wind; sometimes they portend earthquakes but sometimes they have been heard without any earthquake following. Just as the air gives off various sounds when it is struck, so it does when it strikes other things; for every striking is at the same time itself also a being struck, and so the two cases are the same. The sound precedes the shock because sound is thinner and passes through things more readily than wind. But when the wind is weaker than would be needed to move the earth by reason of thinness, the absence of movement is due to its filtering through readily, though because it strikes hard and hollow masses of different shapes it makes various noises, so that the earth sometimes seems to 'bellow' as the portent mongers say.
Water has been known to burst out during an earthquake. But that does not make water the cause of the earthquake. But the wind is the efficient cause whether it drives the water along the surface or up from below: just as winds are the causes of waves and not waves of winds. Else we might as well say that earth was the cause; for it is upset in an earthquake, just like water (for effusion is a form of upsetting). But no, both of these, earth and water, are material causes (being patients, not agents): the true cause is the wind.
The combination of a tidal wave with an earthquake is due to the presence of contrary winds. It occurs when the wind which is shaking the earth does not entirely succeed in driving off the sea which another wind is bringing on, but pushes it back and heaps it up in a great mass in one place. Given this situation it follows that when this wind gives way the whole body of the sea, driven on by the other wind, will burst out and overwhelm the land. This is what happened in Achaea. A south wind was blowing outside, but there was a north wind there; then there was a calm and the wind entered the earth, and then the tidal wave came on and simultaneously there was an earthquake. And this was the more violent as the sea did not allow any exit to the wind that had entered the earth, but shut it in. So in their struggle with one another the wind caused the earthquake, and the wave, by its settling down, the inundation.
Earthquakes are in some local part and often affect a small district only; whereas winds are not local. Such phenomena are in a local part when the evaporations at a given place are also joined by those from the next and unite; this, as we explained, is what happens when there is drought or excessive rain locally. Now earthquakes do come about in this way but winds do not. For earthquakes have their source and origin inside the earth so that everything can be sent together to one place, but the sun cannot do likewise. But the sun has more influence on the evaporations in the air so that, when once they have been given an impulse by its motion, they flow in one direction, determined by the differences of the places.
When the wind is present in sufficient quantity, there is an earthquake. The shocks are horizontal like a tremor; except occasionally, in a few places, where they act vertically, upwards from below, like a pulse. It is the vertical direction which makes this kind of earthquake so rare. The motive force does not easily accumulate in such great quantity in the position required, for the earth secretes far more evaporation along its length than that which is from its depths. Wherever an earthquake of this kind does occur, a quantity of stones comes to the surface of the earth, like boiling in a cauldron (Gk. ὥσπερ τῶν ἐν τοῖς λίκνοις ἀναβραττομένων, as when you throw up things in a winnowing fan.) as we see from Sipylus and the Phlegraean plain and the district in Liguria, which were devastated by this kind of earthquake.
Islands in the middle of the sea are less exposed to earthquakes than those near land. First, the volume of the sea cools the evaporations; it also overpowers them by its weight and so restrains them. Then again, by the action of the winds currents are caused to flow in the sea, but it is not shaken. And because it is so extensive, evaporations do not collect in it but issue from it, and these follow the evaporations that are outside the earth. Those islands near the continent really form part of it: for the intervening sea, because there is so little of it, is not enough to make any difference; but those in the open sea can only be shaken if the whole of the sea that surrounds them is shaken too.
We have now explained earthquakes, their nature and cause, and the most important of the circumstances attendant on their appearance.
238. A severe earthquake does not stop at once (367b32). After the Philosopher has assigned the cause of earthquakes, here he assigns the cause of the accidental things that surround them. And concerning this matter, he does two things.
First, he assigns the cause of the common accidents.
Second, he assigns the cause of certain particular accidents, at islands in the middle of the sea (368b32; [242]).
In regard to the first, he does three things.
First, he assigns the cause of the length of time of earthquakes.
Second, he assigns the cause of certain of its effects, at underground* *noises (368a14; [239])
Third, at earthquakes are in some local part (368b12; [241]), he assigns the cause of the different ways it is related to the earth.
He says first, therefore, that sometimes a severe earthquake does not immediately stop at once or after the first shaking, but sometimes the first continues shaking for forty days and intervening nights in its duration, and after this, for one or even two years. The reason for this is taken from two things, namely, from the quantity of wind and from the shape of the passages through which the wind blows. For when the underground places are narrow and hard so that the wind is beaten back and cannot easily find its way out, then the shocks are most violent, and there it must remain in a cramped space, very much held back, like water that cannot pass through. And therefore just as when a throbbing in the human body is aroused by some passion, for example, anger, and does not cease suddenly or in a short time, but only after much time, as the affection weakens, so does it happen in the wind moving the earth. Thus therefore, the duration of an earthquake is determined by the shape of the place. But it also is determined by the quantity of the matter, because the principle out of which the evaporation was made, from which the wind that shakes the earth was generated, does not immediately exhaust, through its release, all of the material of evaporation. So until, therefore, that matter is consumed, whatever remains of that material causes the shaking, but always more gently, until it comes about that there is such a small amount of evaporation that it cannot move the earth.
Then, when he says underground* *noises (368a14; [239]), he assigns the cause of certain effects of earthquakes.
And first, he gives the cause of the sounds that are caused in the earth.
Second, he assigns the cause of the waters that errupt from the ground because of the earthquake, at water has been known to burst (368a26; [240]).
Third, at the combination of a tidal wave (368a34; [240]), he provides the cause of the waves that occur in the sea.
239. First, therefore, he says that the wind enclosed underground (368a14), which causes the earthquake, sometimes portend an earthquake but sometimes also they make sounds without an earthquake happening. Just as the air gives off various sounds when it is struck, as, for example, a stick or a whip struck upon the air makes sounds, so too, does it make sounds when it itself strikes something bodily. For there is no difference in this regard, whether it strikes or is struck, for every thing that strikes is being struck because of the resistance of whatever is struck. But the sound of this sort, caused by wind enclosed beneath the earth, precedes an earthquake, even though it happens at the same time with it, because sound is thinner and can penetrate more readily through the whole than breath (that is, wind) can do. But this is not to be understood in such a way as if sound were itself a body having parts and thinness, but rather, it is said because sound is more able to come to be in the thinner air than wind is able to. And therefore also sometimes without an earthquake, sounds of this sort occur, for sometimes the wind causing the sound is weaker than would be sufficient to move the earth, and by reason of thinness, the sound can easily filter through such that it arrives at our hearing, even though it cannot move. And so different sorts of sounds are caused, because the enclosed wind strikes hard and hollow masses, formed with different shapes, from which diversity are caused different kinds of sounds, so that the earth sometimes seems to 'bellow' according to what was said by those who in former times were called portent mongers, who said such things so that they would be atoned for by certain sacrifices. For it was common practice among men of old that when unusal events happened in some place, they would be announced to the chief regions, in order that they might inquire from the gods whatever they might allege.
240. Then, when he says, water has been known to burst (368a26), he gives the reason for another effect of the earthquake. And he says that sometimes water has been known to burst out from the earth during an earthquake. Nevertheless, it should not be believed that this is because water is the cause of earthquakes, as Democritus said, but rather, the cause is the wind enclosed in the ground, which moves the water with some violence, whether the water is on the surface of the earth or even under the earth, and in overturning the earth, it makes the water appear, just as waves also happen in the sea because of winds, yet the waves are not the causes of winds. For, by this same argument, someone could say too that the earth is the cause of earthquakes, for the earth is upset because of the earthquake just as water is sent out, for effusion of water is a form of upsetting. But nevertheless, these two, namely, earth and water, are instead related as material in this case, because they are patients and not agents.
Then, when he says, the combination of a tidal wave (368a34), he gives the cause of an additional effect. And he says that when there occur waves in the sea in combination with an earthquake, this is due to a contrariety of winds. For it occurs when the wind enclosed in the earth, which shakes the earth, is not able to drive off the sea completely, because it is driven against by a contrary wind, but nevertheless, by this pushing against and hemming in, a great mass of the sea's water is gathered around the same place. When, therefore, the internal wind is conquered by the external wind, it follows that it is necessary that the sea bursts out over the earth, and it causes a flood, as it were. And he says that this is what happened in Achaea, because a south wind was on the sea, but beneath the earth it was as if there was a northern wind, but when it was made calm, namely, from the contrary battle of the winds, and the northern wind hastened back beneath the earth as if repulsed, then the tidal wave an earthquake happened simultaneously, and especially as the sea resisted and did not give any place for the underground win to blow through, which made it violent. And so as long as the underground wind and the sea inflict their force on one another against each other, the underground wind caused the earthquake, but by its settling down—that is, the sea that brought the internal wind to a halt, in its prevailing—caused the inundation.
241. Then, when he says, earthquakes are in some local part (368b12), he gives the cause of certain accidents of earthquakes that stem from their relation to the earth:
and first, in regard to earthquakes happening only in some part of the earth;
second, in regard to the different ways in which the earth is moved, at when the wind is present (368b22; [242]).
He says first, therefore, that earthquakes are not such that the whole earth is shaken, but are in some local part and frequently affect only up to a small district, but this is not the case with the winds. But an earthquake happens in parts of the earth for the reason that the evaporations that happen in that place and also in neighboring areas come together and unite. As we explained above, dryness sometimes happens in some part, or even rains as well, because of the gathering together of wet evaporation into one place. Now for the same reason, earthquakes come about in some small part of the earth. But this is not the case with the winds that blow in the air, because the evaporations that cause those winds are dispersed to a greater extent, for the winds that cause the earthquakes have their source under the earth, so that everything makes an assault on one place. For the sun not only cannot affect what is beneath the earth as much as it can what is above the earth, such that, namely, it could dissolve the gathering of evaporations under the earth as it does above the earth; but also, the sun can more affect evaporations suspended (that is, raised above) in the air, such that when once they have been given an impulse by the sun's motion, dispersing and melting the evaporations, they then flow in one direction, determined by the difference of the places. And so sometimes the north wind will come to be, at other times, the south wind, and sometimes some other wind will come about. But the flow of underground wind, when it flows together into one place so that an earthquake can happen after their gathering together, is not manifest to us, as is the flow of wind in the air that directs itself into one direction. Hence, winds seem to be spread out and blowing over a long expanse, whereas earthquakes happen in a small place.
**
**
242. Then, when he says, when the wind is present (368b22), he gives the cause of the different ways in which the earth is shaken. And he says that when the wind is gathered together in sufficient quantity, then there is an earthquake, and if the motion is horizontal, it happens as if it were a tremor, except sometimes, but only occasionally, in some places the motion of the earth is like a pulse, as something pushing against the earth upwards from below. But this is rare, because so much evaporation does not easily come together to one place such it can push against the earth above. For the evaporation that is gathered along the length and breadth of the earth is far greater than that which can be gathered from its depths. But wherever an earthquake occurs that is like a pulse, a quantity of stones comes boiling to the surface in that place, like boiling in a cauldron, for the reason that some internal fire is caused by the violence of the motion, and he says that we see this happened in the destruction that took place in certain regions.
Then, when he says, islands in the middle of the sea (368b32), he gives the cause of certain particular accidents. And he says, islands in the middle of the sea, that is, which are found in the deep sea, are less exposed to earthquakes than those islands which are near land, for the volume of the sea cools the evaporations so that they are not released for the generation of winds. And further, by its own weight, the sea overpowers and restrains the earth fixed underneath it so that it is unable to move. Again, the sea flows here and there because of the winds, but the earth positioned underneath it is not shaken by the winds. And because the sea is so extensive in its vastness and depth, the evaporations of the sea are not enclosed in the earth, but are raised above. Moreover, the evaporations of the earth fixed below the sea also follow the evaporations of the sea in spreading above, and so earthquakes are not caused there by evaporations enclosed under the earth. But those islands that are near the continent are as if parts of it; hence it is for the same reason for both these islands and for the land that earthquakes can happen in them. For what is intervening, because it is so little, is not enough to prevent the earthquake. But islands that are farther in the sea can only be shaken if the whole sea is moved that surrounds them, and this is difficult because of the aforementioned causes.
Finally, he recapitulates what he said, and this is manifest in the text itself.
Here ends the exposition of Thomas Aquinas
Continuation of the Commentary by an Unknown Author
Lecture 16
How thunder and lightning are generated
Let us go on to explain lightning and thunder, and further whirlwind, fire-wind, and thunderbolts: for the cause of them all is the same. As we have said, there are two kinds of exhalation, moist and dry, and the atmosphere contains them both potentially. It, as we have said before, condenses into cloud, and the density of the clouds is highest at their upper limit. (For they must be denser and colder on the side where the heat escapes to the upper region and leaves them. This explains why hurricanes and thunderbolts and all analogous phenomena move downwards in spite of the fact that everything hot has a natural tendency upwards. Just as the pips that we squeeze between our fingers are heavy but often jump upwards: so these things are necessarily squeezed out away from the densest part of the cloud.) Now the heat that escapes disperses to the up region. But if any of the dry exhalation is caught in the process as the air cools, it is squeezed out as the clouds contract, and collides in its rapid course with the neighboring clouds, and the sound of this collision is what we call thunder. This collision is analogous, to compare small with great, to the sound we hear in a flame which men call the laughter or the threat of Hephaestus or of Hestia. This occurs when the wood dries and cracks and the exhalation rushes on the flame in a body. So in the clouds, the exhalation is projected and its impact on dense clouds causes thunder: the variety of the sound is due to the irregularity of the clouds and the hollows that intervene where their density is interrupted. This then, is thunder, and this its cause.
It usually happens that the exhalation that is ejected is inflamed and burns with a thin and faint fire: this is what we call lightning, where we see as it were the exhalation colored in the act of its ejection. It comes into existence after the collision and the thunder, though we see it earlier because sight is quicker than hearing. The rowing of triremes illustrates this: the oars are going back again before the sound of their striking the water reaches us.
Lecture 17
Opinions of others regarding thunder and lightning refuted
However, there are some who maintain that there is actually fire in the clouds. Empedocles says that it consists of some of the sun's rays which are intercepted: Anaxagoras that it is part of the upper ether (which he calls fire) which has descended from above. Lightning, then, is the gleam of this fire, and thunder the hissing noise of its extinction in the cloud. But this involves the view that lightning actually is prior to thunder and does not merely appear to be so. Again, this intercepting of the fire is impossible on either theory, but especially it is said to be drawn down from the upper ether. Some reason ought to be given why that which naturally ascends should descend, and why it should not always do so, but only when it is cloudy. When the sky is clear there is no lightning: to say that there is, is altogether wanton.
The view that the heat of the sun's rays intercepted in the clouds is the cause of these phenomena is equally unattractive: this, too, is a most careless explanation. Thunder, lightning, and the rest must have a separate and determinate cause assigned to them on which they ensue. But this theory does nothing of the sort. It is like supposing that water, snow, and hail existed all along and were produced when the time came and not generated at all, as if the atmosphere brought each to hand out of its stock from time to time. They are concretions in the same way as thunder and lightning are discretions, so that if it is true of either that they are not generated but pre-exist, the same must be true of the other. Again, how can any distinction be made about the intercepting between this case and that of interception in denser substances such as water? Water, too, is heated by the sun and by fire: yet when it contracts again and grows cold and freezes no such ejection as they describe occurs, though it ought on their the. to take place on a proportionate scale. Boiling is due to the exhalation generated by fire: but it is impossible for it to exist in the water beforehand; and besides they call the noise 'hissing', not 'boiling'. But hissing is really boiling on a small scale: for when that which is brought into contact with moisture and is in process of being extinguished gets the better of it, then it boils and makes the noise in question. Some—Cleidemus is one of them—say that lightning is nothing objective but merely an appearance. They compare it to what happens when you strike the sea with a rod by night and the water is seen to shine. They say that the moisture in the cloud is beaten about in the same way, and that lightning is the appearance of brightness that ensues. This theory is due to ignorance of the theory of reflection, which is the real cause of that phenomenon. The water appears to shine when struck because our sight is reflected from it to some bright object: hence the phenomenon occurs mainly by night: the appearance is not seen by day because the daylight is too in, tense and obscures it.
These are the theories of others about thunder and lightning: some maintaining that lightning is a reflection, the others that lightning is fire shining through the cloud and thunder its extinction, the fire not being generated in each case but existing beforehand. We say that the same stuff is wind on the earth, and earthquake under it, and in the clouds thunder. The essential constituent of all these phenomena is the same: namely, the dry exhalation. If it flows in one direction it is wind, in another it causes earthquakes; in the clouds, when they are in a process of change and contract and condense into water, it is ejected and causes thunder and lightning and the other phenomena of the same nature. So much for thunder and lightning.
Chapter 27 of 29