In medio quidem igitur et circa medium est quod gravissimum et frigidissimum segregatum, terra et aqua. Circa haec autem et habita his, aer, quemque propter consuetudinem vocamus ignem. Non enim est ignis: excessus enim calidi et velut fervor est quod est ignis. Sed oportet intelligere dicti a nobis aeris, quod quidem circa terram velut humidum et calidum esse, propter vaporem et exhalationem habere terrae: quod autem super hoc, calidum iam et siccum est. Vaporis enim natura humidum et calidum, exhalationis autem calidum et siccum: et est vapor quidem potentia velut aqua, exhalatio autem potentia velut ignis. So at the centre and round it we get earth and water, the heaviest and coldest elements, by themselves; round them and contiguous with them, air and what we commonly call fire. It is not really fire, for fire is an excess of heat and a sort of ebullition; but in reality, of what we call air, the part surrounding the earth is moist and warm, because it contains both vapor and a dry exhalation from the earth. But the next part, above that, is warm and dry. For vapor is naturally moist and cold, but the exhalation warm and dry; and vapor is potentially like water, the exhalation potentially like fire. 24. Postquam philosophus ostendit ignem et aerem non esse corpus caeleste, quod vocatur primum elementum sive primum corpus, nunc intendit ostendere quomodo ignis et aer se habeant ad illud primum corpus. Et circa hoc duo facit: 24. After showing that neither fire nor air is the heavenly body called "first element" or "first body," he now intends to show how fire and air are related to that first body. Concerning this he does two things: primo movet hanc quaestionem, et duas alias necessarias ad propositum; first, he raises this question, and two others necessary for his proposition; secundo solvit eas, ibi: nos autem dicamus et cetera. second, he answers them, at: let us go on (340b4). Prima dividitur in tres, secundum tres quaestiones quas movet: The first is divided into three parts, according to the three questions raised: secunda incipit ibi: et propter quam causam etc.; the second begins at and the reason why (340a21); tertia ibi: de aere igitur et cetera. the third at let us first treat of the air (340a22). Dicit ergo primo quod post praedicta relinquitur perscrutari de ordine aeris et ignis ad primum corpus, scilicet caeleste, ex quo ostensum est ipsum esse aliud praeter ista. He says therefore first that after the above considerations there remains to be examined the relation of air and of fire to the first body, namely, the heavenly body, since it has been shown that it is something other than they. 25. Deinde cum dicit: et propter quam causam etc., movet secundam quaestionem: scilicet, propter quam causam a superioribus stellis causetur caliditas in his locis quae sunt circa terram. Et haec etiam quaestio habet ortum ex praemissis. Videtur enim secundum naturam esse quod simile generet sibi simile: si igitur corpus caeleste non est calidum, quia non est ignis neque aer, ut supra habitum est, remanet in dubio quomodo a corpore caelesti possit causari calor in istis inferioribus. 25. Then when he says, and the reason why (340a21), he places the second question, namely, as to what cause is due the fact that from the upper stars heat is produced in the regions surrounding earth. This question, too, takes its rise from the foregoing considerations. For it seems to be according to nature that like should generate like: if, therefore, the heavenly body is not hot—for it is neither fire nor air, as was shown above—then there remains the problem of how heat can be caused by the heavenly body in these lower bodies. 26. Deinde cum dicit: de aere igitur etc., movet tertiam dubitationem, quae etiam ex praemissis ortum habet. Dixerat enim prius quod oportebat considerare quomodo sit accipienda natura aeris in universo: et hoc ideo, quia multa eorum de quibus determinaturus est, generationem habent in aere. Dicit ergo quod, sicut supra supposuimus, oportet primo aliquid dicere de aere: et sic erit dicendum de aliis duobus quaestionibus motis. Unde statim incipit movere dubitationem ad naturam aeris pertinentem. 26. Then at let us first treat of the air (340a22), he raises the third problem which also arises from the foregoing. For he had said previously that we must inquire how the nature of air in the universe is to be taken, and this for the reason that many of the things concerning which he is about to determine are generated in the air. He says therefore that, as we laid down above, we must first speak of air; then we shall have to discuss the other two questions proposed. Hence he immediately begins to raise the difficulty on the nature of air. Ostensum est enim in libro De generat. quod aqua fit ex aere, et e converso. Cum autem ex condensationibus nubium generatur pluvia, hoc est aerem converti in aquam. Quaerit ergo, si aqua fit ex aere et aer ex aqua, quare in superiori parte aeris non inspissentur nubes ad generationem aquae. Et inducit rationem ad ostendendum quod hoc fieri deberet. Manifestum est enim quod condensatio nubium fit ex frigiditate: nam sicut calidi est rarefacere, ita frigidi inspissare. Locus autem aeris qui est remotior a terra, videtur esse frigidior: quia videntur ibi cessare duae causae calefactionis. For it has been shown in On Generation II that water is produced from air and conversely. Thus, since the rains are generated from the condensings of the clouds, this is air being converted into water. He asks, therefore, if water comes to be from air, and air from water, why is it that, in the upper region of air, clouds are not condensed [thickened] to generate water? And he gives a reason to show that such a thing should happen. For it is plain that condensation of clouds is due to coldness, for just as heat causes things to rarify, so cold causes things to condense. Now it seems that a place should be colder the farther it is from earth, because in such a place the two causes of heating are lacking. Quarum una est propinquitas ad astra, ex quibus causatur calor: et hoc tangit cum dicit quod neque ille locus aeris, superior scilicet, est sic prope astra existentia calida, scilicet secundum effectum, ut caliditas astrorum possit impedire inspissationem nubium. One of these causes is proximity to the stars that cause heat; and this is referred to when he says that the upper region of air is not close enough to the stars which are hot, namely, as to effect, to allow the heat of the stars to prevent the thickening of clouds. Alia causa calefactionis est reverberatio radiorum solis a terra: et hoc tangit cum dicit: neque iterum ille locus superioris aeris est prope radios refractos, idest reverberatos, a terra, qui prohibent congregari nubes prope terram, per hoc quod sua caliditate disgregant consistentias vaporum. Et quod haec secunda causa non impediat congregationem, manifestat per signum. Manifestum est enim quod congregationes nubium fiunt ibi, ubi radii repercussi a terra iam desinunt habere virtutem calefaciendi, propter hoc quod in immensum sparguntur, et sic multum distant a radiis cadentibus; unde non multiplicatur causa caloris. The other cause of heat is solar rays bouncing back from the earth; this cause he refers to when he says that neither is that region of upper air near the rays refracted, i.e., reverberated, from the earth, which rays prevent clouds from gathering close to the earth, inasmuch as their heat breaks down the consistency of the vapors. That this second cause does not prevent congregation he shows through a sign. For it is plain that the comings together of clouds occur where the rays reflected from the earth have already lost their power to heat through being immeasurably dispersed and are thus far distant from the rays that strike the earth; hence the cause of heat is not multiplied. Ad huius autem intelligentiam, sciendum est quod radii procedentes a sole ad terram sunt causa caliditatis. Cum autem radius in terram cadens repercutitur, fit iterum alius radius a terra quasi resursum tendens. Quanto ergo hi duo radii fuerint magis sibi invicem propinqui, tanto plus de calore causatur: quia virtus utriusque radii, scilicet cadentis et reflexi, pertingit ad eandem partem aeris. This last statement becomes plain if we keep in mind the fact that the rays coming from the sun to the earth are what cause heat. When a ray which comes from the sun to earth is reflected, there is now produced another ray as though moving upwards from the earth. The closer these two rays are to each other, the greater the heat produced, because the powers of both rays, i.e., that of the incident ray and that of the reflected ray, act on the same part of the air. Et inde est quod ubi radius solis cadens super terram facit angulum rectum, ibi est maximus calor, quia reflexio fit in eandem partem: quanto vero radius cadens in aliquo loco fecerit angulum maiorem recto, tanto est minus de calore; quia, cum repercussio fiat secundum pares angulos, radius repercussus, propter amplitudinem anguli, multum distat a radio primo cadente. Manifestum est autem quod quanto duae lineae continentes angulum magis procedunt, tanto magis distant abinvicem. Consequently, where a ray of the sun strikes the earth at a right angle, there a maximum of heat is produced, because the ray is reflected into the same direction; when a ray falling on some place strikes at an angle less than a right angle, the heat is by that much less, since, as repercussion takes place according to similar angles, a reflected ray, because of the wideness of the angle, is greatly distant from the ray which first falls. It is plain that the farther two lines containing an angle proceed, the greater becomes the distance between them. Unde quanto magis receditur a terra, ubi fit reverberatio, tanto praedicti duo radii magis distant abinvicem, et est minor calor. Et ideo propter immensam separationem praedictorum radiorum abinvicem in loco superiori, desinit calor, et condensantur ibi nubes propter frigus. Et hoc est quod dicit: nubium congregationes fiunt ubi desinunt iam radii propter spargi in immensum. Hence, the farther one moves from the earth, where reflexion takes place, the farther the aforesaid two rays grow distant from each other, and there is less heat. Therefore, due to the immense separation of the aforesaid rays from one another in the upper region, the heat ceases, and clouds are formed there on account of the cold. And this what he says: gatherings of clouds are produced where the rays now cease because of immeasurable scatterings. Sic igitur utraque causa quae posset impedire congregationem nubium in superiori parte aeris, cessat, ut dictum est. Et cum ibi non condensentur nubes, oportet dicere quod aqua non sit nata fieri ex omni aere: aut si similiter se habet omnis aer ad hoc quod generetur ex eo aqua, oportet quod iste aer qui est circa terram, non solum sit aer, sed sicut vapor, et ex hac causa congregetur ad generationem aquae; superior autem, qui est purus aer, non posset condensari in aquam. Consequently, both causes that could prevent forming of clouds are absent in the upper region of air, as has been said. But since, notwithstanding this, clouds do not form there, it is necessary to spy either that water cannot be formed from just any air, or, if all air is alike so far as being convertible into water is concerned, this air near the earth must not only be air, but as a vapor, and for this reason be gathered to generate water, while the upper air, which is pure air, cannot be condensed into water. Sed hoc non potest esse: quia si totus iste aer qui est circa terram, cum sit tam magnus, vapor est, videtur sequi quod natura aeris et aquae multum excedat alia elementa. Quia superiores distantiae, quae scilicet sunt inter stellas, sunt plenae aliquo corpore, cum nihil sit vacuum, ut in IV Physic. probatum est: impossibile est autem quod sint plenae igne, quia sic omnia alia exsiccarentur, ut supra probatum est: relinquitur ergo quod sint plenae aere, et illud quod est circa terram sit plenum aqua. Sed hic aer est vapor: quia vapor est quaedam disgregatio aquae, idest aqua rarefacta. Et sic positis tribus quaestionibus, quasi colligens subdit quod de praedictis dubitatum sit hoc modo. But this cannot be: for if the totality of air near the earth, since it is such a great amount, is vapor, then it is seen to follow that the nature of air and of water would far exceed the other elements. Because the higher distances, between the stars, are filled with some body (for there is no such thing as a void, as was proved in Physics IV, and they cannot be filled with fire, for this would result in everything's drying up, as was proved above, consequently they must be filled with air, while the region near the earth is filled with water. But this air is vaporous, for vapor is a certain disjoining of water, i.e., rarefied water. Then, having presented the three questions, he adds, as though summarizing, that the problems concerning the aforesaid have been raised in this manner. 27. Deinde cum dicit: nos autem dicamus etc., solvit propositas quaestiones: 27. Then when he says, let us go on (340b4), he solves the questions proposed: et primo eam quae est de ordinatione elementorum; first, the question about the order of the elements; secundo eam quae est de generatione nubium, ibi: eius quidem igitur etc.; second, the one about generation of clouds, at so we must take the reason (340b29); tertio eam quae est de caliditate a stellis in inferioribus causata, ibi: de facta autem caliditate et cetera. third, the one about heat produced in lower bodies by the stars, at as for the heat (341a12). Circa primum tria facit. Primo resumit quod dictum est de natura primi corporis: dicens quod, ad intellectum et eorum quae nunc quaesita sunt, et eorum quae postmodum sunt dicenda, oportet determinando dicere quod supremum corpus usque ad lunam est alterum ab igne et aere, sicut iam ostensum est; et quod in ipso supremo corpore est aliquid purius, et aliquid minus purum vel sincerum: non quod ibi sit aliqua compositio vel mixtio extraneae naturae; sed magis purum dicitur quod est magis nobile, magis virtuosum, magis formale. Unde et habet differentias in virtute et nobilitate: et maxime ista differentia manifesta est ex illa parte qua desinit ad aerem et ad mundum inferiorem qui est circa terram; in luna enim apparet defectus luminis, et quando est plena, apparent in ea quaedam umbrositates. Regarding the first he does three things. First, he repeats what has been said about the nature of the first body and says that for an understanding both of the matters now in question and of matters to be stated later, we must state decisively that the highest body as far as the moon is other than fire and air, as has already been proved, and that there is in that highest body something more pure, and something less pure or sincere, without implying that there is present any composition or mixture of an extraneous nature. Rather "more pure" implies more noble, more virtuous, more formal. Hence it admits of differences both in power and in nobility. This difference is especially evident where it ceases at the air and the lower world surrounding the earth, for in the moon there appear defects of light, and, when it is full, certain dark areas appear. 28. Secundo ibi: lato autem primo elemento etc., ostendit effectum quem habet corpus superius in inferiora. Et dicit quod primo elemento, idest caelo, circulariter moto, et motis corporibus quae sunt in ipso, idest sole et stellis, illa pars inferioris mundi quae est ei propinquior, quasi disgregata seu rarefacta per motum superioris corporis, accenditur: et sic fit caliditas. 28. second, at now the circular motion of the first element (340b10), he shows what effect the higher body has upon the lower ones. And he says that by means of the first element, i.e., the heaven, circularly moved, and the bodies moved in it, namely, sun and stars, that part of the lower world nearest to it, dispersed or rarefied, as it were, by the motion of the superior body, becomes inflamed and heat is produced. Et subiungit rationem, dicens quod hoc oportet intelligere incipiendo. Tota enim natura corporalis quae est sub corpore circulariter moto, est sicut quaedam materia existens in potentia ad caliditatem, frigiditatem, siccitatem et humiditatem, et ad alias passiones et formas quae consequuntur ad haec: et quia materia reducitur in actum a primo agente, natura etiam corporalis fit talis actu per hoc quod participat de motu vel non participat, sed immobilis permanet, a corpore caelesti, quod supra diximus esse causam et principium unde est motus in istis inferioribus. And he gives the reason, saying that to understand this we must go back to the beginning. For the entire bodily nature that exists under the circularly moved body is as a certain matter which is in potency to heat, cold, dryness, and wetness, and to the other passions and forms that result therefrom; and because matter is reduced to act by the first agent, bodily nature also becomes actually such and such by the fact that it participates in the motion, or does not participate but remains immobile, from the heavenly body, which we have previously declared to be the cause and originative principle of the motion in these lower bodies. Non est autem intelligendum quod corpora inferiora recipiant huiusmodi passiones a superioribus tanquam accidentaliter, et non secundum naturam, sicut aqua cum calefit ab igne: sed ipsam naturam vel formam, secundum quam naturaliter sunt calida vel frigida, a superiori corpore recipiunt multo principalius quam a generante; nam primum generationis principium est corpus caeleste. This does not mean that the lower bodies receive such passions from the superior bodies, as it were, incidentally, and not according to nature, as when water becomes heated by fire; rather, the very nature or form according to which they are naturally hot or cold is received more principally from the superior body than from their generator, for the first principle of generation is the heavenly body. Tertio ibi: in medio quidem igitur etc., ostendit ordinem elementorum. Si enim per participationem motus fit calor in istis inferioribus, et per elongationem a motu caelesti e converso fit frigus, necesse est quod illud quod est frigidissimum et gravissimum, idest aqua et terra, sit magis remotum a motu caelesti, existens in medio quantum ad terram, et circa medium quantum ad aquam. Vel dicit circa medium, eo quod medium, cum sit indivisibile, non potest esse locus corporis: sed circa medium, idest centrum mundi, est terra et aqua, centrum autem terrae est in centro totius. Circa haec autem, scilicet terram et aquam, et habita his, idest consequenter ordinata post ipsa, est aer et id quod consueto nomine vocamus ignem, in quibus abundat calor. third at so at the centre (340b19), he shows the order of the elements. For if heat originates in these lower bodies through participation in motion, and if, on the other hand, cold is due to distance from the heavenly motion, then, of necessity, that which is coldest and heaviest, namely, water and earth, is more removed from the heavenly motion and exists in the middle, as the earth does, or about the middle, as water does. Or else he says, around the middle, because the middle, being indivisible, cannot be the place of a body, but rather, earth and water are around the middle, i.e., the center of the world—for the center of the earth is in the center of the whole. Around these, namely, earth and water, and had to these, i.e., ordered in sequence after them, are air, and what is commonly called fire, in which [two] heat abounds. Exponit autem quod dixerat, dicens quod quartum elementum supra aerem ordinatum non proprie vocatur ignis. Ignis enim significat excessum calidi, et est quasi quidam fervor et accensio quaedam; sicut glacies non est elementum, sed est quidam excessus frigoris ad aquam congelatam. Id autem ad quod sic se habet ignis sicut glacies ad aquam, non est nominatum, et ideo nominamus ipsum nomine ignis: sicut si aqua non haberet nomen, et nominaremus elementum aquae glaciem. Sed oportet intelligere quod de toto isto corpore quod a nobis dicitur aer, una pars, quae est propinqua terrae, est quasi calida et humida, propter id quod habet de vapore et exhalatione terrae. He explains his statement that the fourth element, i.e., the one located above air, is not strictly called "fire." For "fire" signifies an excess of heat and is, as it were, a certain intensity and igniting. In the same way, ice is not an element but a certain superabundance of coldness producing congealed water. Now that to which fire is related in the way that ice is related to water has no name; so we call it by the name of fire. It is as though water should have no name and we should call the element of water, "ice." But we must understand that in regard to that whole body we call "air," one part, the part nearest the earth, is as though hot and moist on account of vapor, and exhalation from the earth. Sic enim elementa sunt ordinata, secundum quod eorum naturae competit: unde quia aer secundum naturam suam est calidus et humidus, sic est dispositus ut vaporem terrae suscipiat, ad eius calorem et humiditatem servandam. Sed illa pars corporis quod communiter vocatur aer, quae est superior, est calida et sicca; et hanc partem vocamus elementum ignis. Et sic aer nomen commune est duobus elementis. Et quia dixerat de vapore et exhalatione terrae, ostendit differentiam inter ea. Et dicit quod natura vaporis est esse humidum et calidum, natura autem exhalationis est esse calidum et siccum: et sic vapor, propter humiditatem, est quasi in potentia ad aquam; exhalatio autem, propter siccitatem, est quasi in potentia ut igniatur. For the elements are arranged in a manner that befits their nature; therefore, because air is naturally hot and moist, it is disposed to receive vapor from the earth to preserve its heat and moisture. But that part of the body commonly called "air" which is higher, is hot and dry; and this upper part we call the element "fire." In this way the name "air" is common to two elements. And because he had spoken about vapor and exhalation from the earth, he shows the difference between them and says that the nature of vapor is to be moist and hot, whereas the nature of an exhalation is to be hot and dry. As a result, vapor is, on account of its moistness, in potency to water; but an exhalation, on account of its dryness is, as it were, in potency to be ignited. Lectio 5 Lecture 5 Solvuntur aliae duae quaestiones: quare nempe in superiori parte aeris non generantur nubes; et propter quam causam corpora caelestia, licet non sint calida in sui natura, causant calorem in istis inferioribus The remaining two questions about the upper region solved Eius quidem igitur quod in eo qui sursum loco non constare nubes, hanc existimandum causam esse, quia non inest aer solum, sed magis velut ignis. So we must take the reason why clouds are not formed in the upper region to be this: that it is filled not with mere air but rather with a sort of fire. Nihil autem prohibet et propter eam quae in circuitu lationem prohiberi nubes constare in superiori loco. Fluere enim necesse est omnem qui in circuitu aerem, quicumque non intra peripheriam capitur definitam, ut et terra sphaerica sit tota. Videtur enim et nunc ventorum generatio in stagnantibus terrae locis, et non excedere ventos altos montes. Fluit autem in circuitu, quia simul trahitur cum totius circulatione: ignis quidem enim cum eo quod sursum elemento, cum igne autem aer continuus est. Quare et propter motum prohibetur congregari in aquam. Sed semper quaecumque pars ipsius gravetur, extruso in superiorem locum calido, deorsum fertur, alia autem in parte simul fertur sursum exhalato igni: et sic continue hoc quidem perseverat aere plenum, hoc autem igne, et semper aliud et aliud fit unumquodque ipsorum. However, it may well be that the formation of clouds in that upper region is also prevented by the circular motion. For the air round the earth is necessarily all of it in motion, except that which is cut off inside the circumference which makes the earth a complete sphere. In the case of winds it is actually observable that they originate in marshy districts of the earth; and they do not seem to blow above the level of the highest mountains. It is the revolution of the heaven which carries the air with it and causes its circular motion, fire being continuous with the upper element and air with fire. Thus its motion is a second reason why that air is not condensed into water. But whenever a particle of air grows heavy, the warmth in it is squeezed out into the upper region and it sinks, and other particles in turn are carried up together with the fiery exhalation. Thus the one region is always full of air and the other of fire, and each of them is perpetually in a state of change. De eo quidem igitur quod est non fieri nubes neque in aquam congregationem, et quomodo oportet accipere de loco intermedio astrorum et terrae, et quo est corpore plenus, tanta dicta sunt. So much to explain why clouds are not formed and why the air is not condensed into water, and what account must be given of the space between the stars and the earth, and what is the body that fills it. De facta autem caliditate quam exhibet sol, magis quidem secundum seipsum et diligenter in his quae de sensu convenit dicere: calidum enim passio quaedam sensus est. Propter quam autem causam fit, non talibus existentibus illis secundum naturam, dicendum et nunc. As for the heat derived from the sun, the right place for a special and scientific account of it is in the treatise about sense, since heat is an affection of sense, but we may now explain how it can be produced by the heavenly bodies which are not themselves hot. Videmus itaque motum, quod potest disgregare aerem et ignire, ut et lata liquefacta videantur saepe. We see that motion is able to dissolve and inflame the air; indeed, moving bodies are often actually found to melt.