Pruina quidem, quando vapor congelatur priusquam in aquam condensetur iterum (fit autem, in hieme et magis in hiemalibus locis); ros autem, cum concretus fuerit in aquam vapor, et neque sic fuerit aestus ut exsiccetur sursum ductus, neque sic frigus ut congeletur vapor ipse; propter quod aut locus calidior aut tempus. Fit enim ros magis in temperie et in temperatis locis: pruina autem, sicut dictum est, contrarie. Palam enim quod vapor calidior aqua, habet enim elevantem adhuc ignem: quare amplioris frigiditatis ipsum coagulare. When the vapor is frozen before it has condensed to water again it is hoar-frost; and this appears in winter and is commoner in cold places. It is dew when the vapor has condensed into water and the heat is not so great as to dry up the moisture that has been raised nor the cold sufficient (owing to the warmth of the climate or season) for the vapor itself to freeze. For dew is more commonly found when the season or the place is warm, whereas the opposite, as has been said, is the case with hoar-frost. For obviously vapor is warmer than water, having still the fire that raised it: consequently more cold is needed to freeze it. Fiunt autem ambo serenitate et tranquillitate neque enim elevabuntur non existente serenitate, neque constare poterunt utique vento flante. Both dew and hoar-frost are found when the sky is clear and there is no wind. For the vapor could not be raised unless the sky were clear, and if a wind were blowing it could not condense. Signum autem quia fiunt haec propterea quod non longe suspenditur vapor: in montibus quidem etenim non fit pruina. Causa autem una quidem haec, quia sursum ducitur ex submissis et humectis locis: quare, velut onus portans maius sursum ducens caliditas quam secundum ipsam, non potest elevare ipsum ad multum locum altitudinis, sed prope dimittit iterum. Alia autem, quia et fluit maxime aer existens in altis, qui dissolvit consistentiam talem. The fact that hoar-frost is not found on mountains contributes to prove that these phenomena occur because the vapor does not rise high. One reason for this is that it rises from hollow and watery places, so that the heat that is raising it, bearing as it were too heavy a burden cannot lift it to a great height but soon lets it fall again. A second reason is that the motion of the air is more pronounced at a height, and this dissolves a gathering of this kind. Fit autem ros ubique australibus, non borealibus, praeterquam in Ponto. Ibi autem contrarie: borealibus quidem enim fit, non australibus. Everywhere, except in Pontus, dew is found with south winds and not with north winds. There the opposite is the case and it is found with north winds and not with south. Causa autem similiter, sicut quia temperie quidem fit, hieme autem non fit. Auster quidem enim temperiem facit, boreas autem hiemem, frigidus enim: quare ex hieme exhalationis extinguit caliditatem. The reason is the same as that which explains why dew is found in warm weather and not in cold. For the south wind brings warm, and the north, wintry weather. For the north wind is cold and so quenches the heat of the evaporation. In Ponto autem auster quidem non sic facit temperiem ut fiat vapor: boreas autem, propter frigiditatem, antiperistasim faciens, calidum congregat; quare plus vaporat magis. Saepe autem hoc et in exterioribus locis est videre factum; vaporant enim putei borealibus magis quam australibus: sed borealia quidem extinguunt antequam constet aliqua multitudo, in australibus autem sinitur congregari exhalatio. But in Pontus the south wind does not bring warmth enough to cause evaporation, whereas the coldness of the north wind concentrates the heat by a sort of recoil, so that there is more evaporation and not less. This is a thing which we can often observe in other places too. Wells, for instance, give off more vapor in a north than in a south wind. Only the north winds quench the heat before any considerable quantity of vapor has gathered, while in a south wind the evaporation is allowed to accumulate. Water, once formed, does not freeze on the surface of the earth, in the way that it does in the region of the clouds. 94. Postquam Philosophus determinavit de his quae causantur ex exhalatione sicca ad supremum locum aeris elevata, hic determinat de his quae causantur ex exhalatione humida. 94. After determining concerning phenomena caused from the hot exhalation lifted to the highest place of the air, the Philosopher here determines about phenomena caused from the moist exhalation. Et primo de his quae causantur ex exhalatione humida super terram; First, about phenomena caused above the earth from the moist exhalation; secundo de his quae causantur ex exhalatione humida in terra, ibi: de ventis autem et cetera. second, about those caused on the earth from the moist exhalation, at let us explain the nature of winds (349a12). 95. Circa primum duo facit. 95. Regarding the first he does two things: Primo ostendit de quo est intentio: dicens quod nunc dicendum est de his quae fiunt in loco qui secundum situm, descendendo, est secundus post locum supremum aeris, in quo fiunt ea quae dicta sunt, sed ascendendo est primus, immediatus circa terram; quae inferior pars aeris est. Iste enim locus est communis et aquae et aeri: quia in eo aer est secundum naturalem ordinem elementorum, et aqua ex vaporibus elevatis ibi generatur. Unde non solum est communis aquae et aeri, sed etiam eis quae accidunt circa generationem ipsius aquae et aeris, quae fiunt superius dum aqua resolvitur in vapores, qui pertinent ad naturam aeris, et vapores congregantur in aquam. Ostendit etiam modum determinandi de istis, dicens quod debemus sumere primo principia communia et causas omnium horum accidentium. first, he shows what his intention concerns and says that we must now discuss the things which come to be in the region which, going downwards, is the second after the uppermost region of the air (where the phenomena already discussed take place), but which, going upward, is first, i.e., the region immediately around the earth: this region is the lower region of air. It is the region common both to water and to air; because in it air exists according to the natural order of the elements, and water is generated there from vapors borne aloft. Hence not only is it common to water and air, but also to the phenomena attending the generation of that water and air. These generations take place on high, when water is resolved into vapors (which pertain to the nature of air) and vapors are gathered into water. He also indicates the method for determining these matters and says that we should first take the common principles and causes of all these things that happen. 96. Secundo ibi: quod quidem igitur etc., determinat propositum. 96. second at the efficient (346b20), he determines the proposition. Et primo ponit ea quae communiter pertinent ad causam omnium huiusmodi passionum; First, he posits what pertains commonly to the cause of all passions of this kind; secundo determinat de singulis passionibus, ostendens differentiam inter eas, ibi: elevato autem humido et cetera. second, he determines concerning each of them separately, showing wherein they differ, at so the moisture is always raised (347a8). Circa primum tria facit. About the first he does three things: Primo ponit causam effectivam harum passionum. Et dicit quod illud quod est causa sicut movens et principale et primum principium omnium harum passionum, est circulus zodiacus, in quo manifeste movetur sol, qui et disgregat resolvendo vapores a terra, et congregat eos per suam absentiam: frigore enim invalescente in aere per absentiam solis, nubes condensantur in aquam. Et ideo subiungit quod ex hoc quod quandoque fit prope nos, quandoque autem elongatur a nobis, existit causa generationis et corruptionis. Fit prope autem nobis secundum proprium motum, quando accedit ad signa Septentrionalia: elongatur autem a nobis, dum moratur in signis meridionalibus. first, he sets down the efficient cause of these passions and says that all these passions have as their cause, in the sense of the movent, and primary, and first principle, the circle of the Zodiac in which the sun clearly moves, which both separates the vapors, by resolving them from earth, and unites them by its absence: for when coldness increases in the air on account of the sun's absence, clouds are condensed into water. Accordingly he adds that from its being at one time near us, and at another time away from us, the sun is the cause of generation and corruption. It gets near us, when by its own motion it approaches the northern signs; it is moved away from us, when it tarries in the southern signs. 97. Secundo ibi: manente autem terra etc., ostendit causam materialem harum passionum. Et dicit quod, cum terra quiescat in medio, illud humidum aqueum quod est circa ipsam, tum a radiis solis tum ab alia caliditate quae est a superioribus corporibus, resolvitur in vaporem, et sic subtiliatum per virtutem calidi sursum fertur. 97. second at now the earth remains (346b23), he shows the material cause of these passions and says that, since the earth is at rest in the center, the aqueous humor surrounding it is, both through the agency of the sun's rays and through other heat from the higher bodies, resolved into vapor and, being thus refined by the virtue of the heat, borne aloft. 98. Tertio ibi: caliditate autem etc., ostendit modum generationis horum de quibus intendit. Et circa hoc tria facit. 98. third at but when the heat (346b26), he shows the way in which the things under discussion are generated. About this he does three things: Primo ponit in communi modum generationis harum passionum. Et dicit quod vapor qui sursum fertur per virtutem caloris, deseritur a caliditate quae sursum eum ferebat. Quod quidem contingit dupliciter: uno modo per hoc quod id quod erat subtilius et calidius in vapore, elevatur ulterius ad superiorem locum exhalationis siccae, et sic residua pars vaporis remanet frigida; alio modo per hoc quod calor qui est in vapore extinguitur, propter hoc quod longe elevatur a terra in aere qui est supra terram, ubi deficit calor propter hoc quod radii reverberati a terra in immensum sparguntur, ut supra dictum est. Sic igitur deficiente calore calefaciente et elevante vaporem aqueum, vapor aqueus redit ad suam naturam, coadunante etiam frigiditate loci; et sic infrigidatur, et infrigidatus inspissatur, et inspissatus cadit ad terram. first, he states in general the way these passions are generated and says that the vapor borne aloft by the power of the heat is abandoned by the heat which bore it aloft. This happens in two ways: in one way by the fact that the finer and warmer elements in the vapor are raised higher still, to the upper region of the dry exhalation—consequently, the portion of vapor left behind remains cold; in another way by the fact that the heat in the vapor is quenched by having been lifted far from the earth, in the air above the earth where heat is feeble on account of the rays reflected from the earth being scattered far apart, as was stated above. Therefore, when the heat which warmed and elevated the moist vapor runs out, this vapor returns to its nature, with the coldness of the region condensing it; thus it becomes cool, and after being cooled, it is thickened, and once thickened, it falls to earth. 99. Secundo ibi: est autem quae quidem etc., ostendit quid sit medium in praedictis transmutationibus. In prima enim transmutatione, secundum quam aqua subtiliatur et elevatur, medium est vapor: nam ipsa exhalatio resoluta ab aqua vocatur vapor, qui est medius inter aerem et aquam. In illa autem transmutatione secundum quam aer condensatur in aquam, medium est nubes, quae est via generationis aquae. Sed cum nubes condensatur in aquam, id quod est residuum de nube, quod scilicet in aquam condensari non potuit, est caligo nebulae. Et ideo nebula magis est signum serenitatis quam pluviae: quia nebula est quasi quaedam nubes sterilis, idest sine pluvia, quae est naturalis effectus nubis. Contingit tamen aliquando nebulam elevari in ipsa exhalatione vaporum, antequam condensentur in nubem perfecte: et tunc nebula potest esse signum pluviae. 99. second at the exhalation of water is (346b32), he shows what intermediates are involved in these transmutations. In the first transmutation, in which water is subtilized and raised up, the intermediate is vapor: for the very exhalation resolved from the water is called "vapor," which is intermediate between air and water. In that transmutation in which air is condensed into water, the medium is a cloud, which is a step toward the generation of water. But when the cloud is condensed into water, that which is left over in the cloud, i.e., whatever could not be condensed into water, is called the fog of mist. That is why mist is more a sign of clear than of rainy weather: for mist is, as it were, a barren cloud, i.e., devoid of rain, which is the natural effect of a cloud. However it sometimes happens that mist is carried up along with the vaporous exhalations before they are perfectly condensed into a cloud—and then mist can be a sign of rain. 100. Tertio ibi: fit autem circulus iste etc., ostendit quomodo in praedictis transmutationibus representatur similitudo primae causae moventis, scilicet circulationis solis. Attenditur enim quaedam circulatio in praedictis transmutationibus, dum aqua resolvitur in vapores, qui condensantur in nubes, et nubes in aquam, quae cadit in terram. Dicit ergo quod ista circularis transmutatio imitatur circularem motum solis: sol enim permutatur ad diversas partes caeli, puta ad Septentrionem et meridiem, et circulatio ista completur in hoc quod vapores ascendunt sursum et descendunt deorsum. Sed oportet intelligere quod iste fluxus vaporum ascendentium et descendentium, sit quasi quidam fluvius circularis communis aeri et aquae: nam quod aqua resolvitur in vaporem, ad aerem attinet, quod autem nubes in aquam condensantur, ad aquam. Cum ergo sol prope existit, iste fluvius vaporum ascendit sursum; cum autem elongatur sol, descendit deorsum; et hoc indesinenter fit secundum ordinem praedictum. Unde concludit quod forte antiqui dicentes Oceanum esse quendam fluvium circumdantem terram, occulte loquebantur de hoc fluvio, qui circulariter fluit circa terram, ut dictum est. 100. third at so we get a circular process (346b35), he shows how the above-mentioned transmutations bear an analogy to the first movent cause, i.e., to the circling of the sun. For a certain circling is discernible in the above-mentioned transmutations, as water is refined into vapors which are condensed into clouds, and the clouds into water, which falls to earth. He says therefore that this circular transmutation imitates the circular movement of the sun—for the sun is changed to diverse parts of the heaven (for example, to the north and to the south); and that cycle is completed in the fact that vapors ascend upwards and descend downwards. But we should understand this flow of ascending and descending vapors as a certain circular stream common to air and water: for the resolving of water into vapor pertains to the air, while the condensing of clouds into water pertains to the water. When, therefore, the sun is near, this river of vapors flows upward; when the sun is away, it flows downward; and this goes on without interruption in the order described. From this he concludes that perhaps the ancients, in speaking of Oceanus as a certain river surrounding the earth, were cryptically speaking of this river, which, as was said, flows circularly around the earth. 101. Deinde cum dicit: elevato autem humido etc., determinat de praedictis passionibus in speciali, ostendendo differentias earum adinvicem. Et dividitur in duas partes: 101. Then when he says, so the moisture is always raised (347a8), he discusses the foregoing passions in detail, by pointing out their mutual differences. And it is divided into two parts: in prima determinat de generatione illorum quae manifestiorem habent causam; in the first he determines about the generation of those phenomena whose cause is quite plain; in secunda de generatione grandinis, circa quam est maior difficultas, ibi: ipsa autem aqua et cetera. in the second about the generation of hail, concerning which there is greater difficulty, at from the latter (347b12). 102. Circa primum duo facit. 102. About the first he does two things: Primo determinat de pluviis: dicens quod cum humidum aqueum elevatur ex virtute calidi, et iterum fertur deorsum propter infrigidationem, secundum quasdam differentias, huiusmodi passionibus aeris diversa nomina imponuntur. Quia quando per modicas partes vapores inspissati in aquam cadunt, tunc dicuntur psecades, idest guttae, sicut aliquando contingit quod parvae guttae decidunt: quando vero secundum maiores partes decidunt guttae ex vaporibus generatae, vocatur pluvia. first, he determines about rain and says that when watery moisture is elevated through the power of heat and is again brought down on account of cooling, different names, based on varying characteristics, are given to these passions of air. For when the vapors condensed into water in small parts fall, then they are called psecades (347a8), i.e., drops, as occasionally happens, when small drops fall; but when the drops of a larger size generated from the vapors fall, this is called "rain." 103. Secundo ibi: ex eo autem quod de die etc., determinat de rore et pruina. Et circa hoc tria facit. 103. second at some of the vapor that is formed by day (347a13), he determines about dew and frost. Primo determinat modum generationis eorum. Et dicit quod ros et pruina contingunt ex hoc quod de die, sole existente super terram, aliquid evaporat ex humido aqueo propter solis calorem; quod quidem evaporatum non multum suspenditur vel elevatur super terram, propter hoc quod ignis, idest calor elevans huiusmodi vaporem, est parvus in comparatione ad humorem aqueum qui elevatur. Et ita, cum de nocte infrigidatus fuerit aer, inspissatur ille vapor elevatus de die, et cadit in terram, et vocatur ros vel pruina: ut ita se habeat accessus solis et recessus secundum motum diurnum ad generationem roris et pruinae, secundum quod se habet ad generationem pluviae secundum motum proprium, secundum quod accedit et recedit in aestate et hieme. First, he determines the manner in which they are generated. And he says that they arise from the fact that, when the sun is above the earth in daytime, something evaporates from the watery moisture because of the sun's heat, but this evaporation is not suspended or raised very high above the earth, for the simple reason that the fire, i.e., the heat raising this vapor, is slight in comparison with the watery moisture elevated. Consequently, when the air cools at night, the vapor elevated during the day condenses and falls to earth and is called "dew" or "frost." The approach and departure of the sun in its diurnal course has the same relation to the generation of dew and frost as, in the generation of rain, its proper motion has according as it approaches and departs in summer and winter. 104. Secundo ibi: pruina quidem etc., ostendit differentiam eorum: dicens quod pruina fit, quando vapor prius congelatur quam condensetur in aquam; et propter hoc fit in hieme et in hiemalibus locis, idest in frigidis locis. Sed ros fit, quando vapor inspissatur in aquam, et neque est tantus aestus quod vapor elevatus desiccetur, neque est tantum frigus quod vapor congeletur. Et ideo oportet quod sit aut in tempore aut in loco calido: quia ros semper fit in tempore temperato et in locis temperatis, sed pruina, sicut dictum est, fit in tempore et loco magis frigidis. Cum enim vapor sit calidior aqua, quia adhuc est in eo aliquid de calore elevante, maior frigiditas requiritur ad congelationem vaporis quam aquae; et sic pruina nunquam fit nisi in magno frigore. 104. second at when the vapor (347a16), he points out their difference and says that frost occurs when the vapor is frozen before it is condensed into water: for this reason it occurs in winter and in wintry, i.e., frigid, places. But dew occurs when the vapor is thickened into water and there is neither enough heat to dry out the vapor that has been raised, nor enough cold for the vapor to freeze. Hence dew must occur either during warm seasons or in warm places: because dew occurs always in temperate times or temperate places, but frost in times and places that are colder, as has been said. For since vapor is warmer than water (because some of the heat raising it is still in it) more cold is needed to freeze vapor than to freeze water: as a result, frost never occurs except where there is much cold. 105. Deinde cum dicit: fiunt autem ambo etc., ostendit qualiter existente aere disposito, fit ros et pruina. 105. Then when he says, both dew and hoar-frost are found (347a26), he shows the conditions of disposed air under which dew and frost occur. Et primo ostendit hoc communiter quantum ad utrumque; First, he shows this generally as to both; secundo specialiter de rore, ibi: fit autem ros ubique et cetera. second, specially for dew, at everywhere (347a35). Circa primum duo facit: About the first he does two things: primo ostendit quod proponit; first, he shows what he is proposing; secundo ponit quoddam signum praedictorum, ibi: signum autem et cetera. second, he gives a sign of the aforesaid, at the fact that (347a30). Dicit ergo primo quod tam ros quam pruina fiunt cum aer fuerit serenus absque nubibus et pluvia, et tranquillus absque vento. Quia si non sit serenus, non possunt elevari vapores de die, propter defectum caloris: si autem non fuerit tranquillitas, vento flante, non poterunt vapores condensari, ut generetur ros; nam ventus, commovendo aerem, impedit congregationem vaporum. He says therefore first, that both dew and frost occur when the air is clear, without clouds and rain, and calm, without wind. Because if it is not clear, vapors cannot be lifted up during the day due to the lack of sufficient heat: if it is not calm, but windy, the vapors could not be condensed to form dew—for the wind, in agitating the air, prevents the vapors from massing together.