Quare, si quidem et de apparendo cometas acceptamus causam tanquam dictam mediocriter, et de lacte eodem modo existimandum habere: quod enim ibi circa unum est passio coma, hoc circa circulum quendam accidit fieri eandem. Et est lac, ut est dicere velut definitum, maximi circuli propter segregationem coma. Propter quod, quemadmodum prius diximus, non multi neque saepe fiunt cometae; quia continue segregata est, et segregatur secundum unamquamque periodum, in hunc locum semper talis consistentia. Hence if we accept the cause assigned for the appearance of comets as plausible we must assume that the same kind of thing holds good of the milky way. For the fringe which in the former case is an affection of a single star here forms in the same way in relation to a whole circle. So if we are to define the milky way we may call it 'a fringe attaching to the greatest circle, and due to the matter secreted'. This, as we said before, explains why there are few comets and why they appear rarely; it is because at each revolution of the heavens this matter has always been and is always being separated off and gathered into this region. De factis quidem igitur in eo qui circa terram mundo continuo lationibus, dictum est: de discursu quidem astrorum, et ignita flamma, adhuc autem de cometis et vocato lacte. Fere enim sunt tot passiones apparentes circa hunc locum. We have now explained the phenomena that occur in that part of the terrestrial world which is continuous with the motions of the heavens, namely, shooting-stars and the burning flame, comets and the milky way, these being the chief affections that appear in that region. 86. Reprobatis opinionibus aliorum de circulo lacteo, hic ponit propriam opinionem. Et circa hoc duo facit: 86. Having rejected the opinion of others about the milky circle, he now presents his own opinion. About this he does two things: primo resumit quaedam superius dicta, quae sunt utilia ad propositum manifestandum; first, he recalls previous statements useful for explaining the proposition; secundo manifestat propositum, ibi: quod itaque secundum unum astrorum accidit et cetera. second, he manifests the proposition, at now we must assume that what happens in the case of the stars (345b6). Resumit autem duo: He recalls two things: primo quidem quod supra dictum est de positione siccae exhalationis, et eius inflammatione. Unde dicit quod vult resumere id quod supra posuit tanquam principium. Dictum est enim supra quod communiter vocatur aer totum hoc quod est intra terram et globum lunarem; huius autem suprema pars, licet non proprie possit dici ignis, quia ignis significat excessum in caliditate, sicut glacies in frigore, tamen illa pars superior aeris habet virtutem ignis, quia est calida et sicca; ita quod, cum aer per motum caelestem disgregatur, talis consistentia exhalationis praedictae segregatur a terra et ab aere inferiori, et elevatur sursum, et ex hoc dicimus apparere stellas cometas. first, what was previously said about the location of the dry exhalation and of its kindling. Hence he says that he wants to recall what he previously laid down as a principle. For it has been previously said that everything between earth and the globe of the moon has the common name of "air," while the highest part thereof, although it cannot strictly be called "fire" (because fire denotes a superabundance of heat, just as does ice with respect to cold), yet that upper part of the air does have the virtue of fire, because it is hot and dry—with the result that, when the air is separated by the heavenly motion, a certain consistency of the exhalation already mentioned is collected from the earth and lower air and lifted upward; and we say that it is from this that comet stars appear. 87. Secundo ibi: tale itaque oportet etc., resumit quod dictum est supra de uno modo apparitionis cometae. Et dicit quod oportet intelligere aliquid simile esse in lacteo circulo, quod fit in cometis, quando cometa non fuerit aliqua exhalatio elevata et ignita per se existens absque aliqua stella, sed fit eius apparitio ab aliqua stellarum fixarum vel errantium, sicut dictum est. Quia tunc apparent cometae propter hoc, quod tales exhalationes elevatae consequuntur motum stellarum quae videntur cometae; sicut etiam solem sequitur talis adunata exhalatio, ex qua, propter repercussionem radiorum, apparet halo, cum aer ad hoc fuerit dispositus. 87. second at we must suppose (345b35), he recalls what he previously said concerning one of the ways that account for the appearance of a comet. And he says that we should understand in the milky circle something akin to what takes place in comets when the comet is not an exhalation borne aloft and ignited, and existing by itself apart from any star, but is an apparition deriving from one of the fixed or wandering stars, as was said. For in those cases comets appear because such elevated exhalations accompany the course of the stars that appear as comets; just as the sun is accompanied by such a collected exhalation, from which, as a result of reflected rays, a halo appears, when the air is disposed for such. 88. Deinde cum dicit: quod itaque secundum unum astrorum accidit etc., manifestat propositum, ostendens quae sit causa apparitionis lactei circuli. Et circa hoc tria facit: 88. Then when he says, now we must assume that what happens in the case of the stars (345b6), he manifests the proposition, showing what is the cause of the appearance of the milky circle. About this he does three things: primo proponit causam apparitionis lactei circuli; first, he proposes the cause of the appearance of the milky circle; secundo inducit signum eorum quae dicta sunt, ibi: signum autem etc.; second, he introduces a sign to support what he said, at a proof of the theory is this (345b23); tertio concludit propositum, ibi: quare si quidem et cetera. third, he concludes the proposition, at hence if (346b1). Circa primum duo facit. Regarding the first he does two things. Primo ostendit causam apparitionis lactei circuli. Et dicit quod illud quod accidit in apparitione secundum unam stellam, oportet accipere esse factum circa totum caelum et circa totum motum ipsius: quia rationabile est quod, si motus unius stellae attrahit et circumducit aliquam exhalationem, quod multo magis hoc possit facere motus omnium stellarum; et praecipue in loco illo caeli, ubi apparent frequentissimae stellae et plurimae et maximae. First, he shows the cause of the appearance of the milky circle and says that what happens with respect to the appearance of one star should be understood as happening with respect to the entire heaven and its entire course—because it is reasonable, if the motion of one star attracts and carries an exhalation along, that this should be all the more true of the motion of all the stars, and especially in that region of the heaven where there appears a very large collection of stars, greatest both in number and size. 89. Secundo ibi: qui quidem igitur animalium etc., ostendit causam quare in hac determinata parte caeli circuli lactei claritas apparet. Et dicit quod circulus animalium, qui dicitur zodiacus, dissolvit adunationem praedictae exhalationis, propter hoc quod per zodiacum movetur sol et alii planetae. Et haec est etiam causa propter quam, ut plurimum, cometae non apparent in zodiaco, sed extra tropicos, ut dictum est. Et haec est etiam causa propter quam circa solem et lunam non fit coma: quia videlicet per motum solis et lunae citius disgregatur exhalatio (quam diximus esse causam apparitionis cometae et lactei circuli), quam ut possit adunari ad causandum apparitiones praedictas. Sed iste circulus in quo apparet nobis videntibus lactea claritas, et est unus maximorum circulorum, quia dividit sphaeram per medium; et est sic dispositus secundum situm, ut ex utraque parte multum excedat utrumque tropicum, scilicet hiemalem et aestivum, licet intersecetur a zodiaco. 89. second at now the circle of the zodiac (345b11), he shows the cause why it is in that determinate part of the heaven that the brightness of the milky circle appears. And he says that the circle of the animals, called the "Zodiac," dissolves the accumulated mass of the above-mentioned exhalation, because of the fact that the sun and the other planets are moved through the Zodiac. This also explains why, for the most part, comets do not appear in the Zodiac, but outside the tropics, as was said. Moreover, this also is the cause why no fringe [coma] appears around the sun and moon: namely, because the motions of the sun and moon separate the exhalation (which we have said to cause the appearance of a comet and of the milky circle) faster than it can accumulate to cause these appearances. But that circle in which a milky brightness appears to us observers is both one of the greatest circles (for it divides the sphere in half), and is so located that in both directions it far exceeds both the tropic circles, namely, the winter and the summer one, even though it is intersected by the Zodiac. Et etiam hic locus istius circuli est plenus magnis stellis fulgidis, et quae propter frequentiam et spissitudinem vocantur sporadicae, idest seminatae in caelo (quod etiam manifeste oculis videri potest); ita quod propter huiusmodi causam semper in tali parte caeli adunetur exhalatio; quia videlicet in hac parte caeli est efficax virtus stellarum ad attrahendam exhalationem, et non est causa vehemens quae impediat eius adunationem, sicut accidit sub zodiaco circulo. Ista igitur exhalatio adunata sub tali parte caeli, facit ibi videri lacteam claritatem, sicut et exhalatio consequens aliquam stellam, facit ibi videri comam. Moreover, this place of that circle is filled with bright stars so numerous and thick that they are called sporadic, i.e., sowed in the heaven (this can be observed with the naked eye); as a result, an exhalation is always gathered together in such an area of the heaven, since, namely, there is in this region of the heaven stellar virtue powerful enough to attract the exhalation, and no vehement cause impeding its accumulating, as happens in the zodiacal circle. Accordingly, the exhalation accumulated in that region of the heaven causes a milky brightness to be seen there, just as the exhalation accompanying a star makes a fringe appear. 90. Deinde cum dicit: signum autem etc., manifestat quod dictum est, per signum: dicens quod signum praedictorum est, quod in ipso lacteo circulo unus eius semicirculus duplatur, et habet amplius de lumine. Cuius causa est, quia in illo semicirculo sunt plures stellae et magis frequentes quam in alio, ac si nulla esset alia causa claritatis apparentis, quam motus astrorum plurimorum frequentium. Quia si in isto circulo apparet claritas in quo plures stellae ponuntur, et in illa eius parte plus apparet in qua sunt stellae plures et magis frequentes, verisimile est multitudinem stellarum esse causam huius apparitionis. Quod autem dictum est de isto circulo et de stellis in eo existentibus, potest considerari ex descriptione: quia astrologi describunt totam sphaeram cum stellis in ea existentibus. 90. Then when he says, a proof of the theory is this (345b23), he shows what he has said with a sign, and says that a sign of the foregoing is that in the milky circle one of its semicircles is doubled and has more light. The reason for this is that in that semicircle there are more stars there and closer together than in the other semicircle, as though there were no other cause of the visible brightness than the movements of a great many clustered stars. For if a brightness appears in that circle in which there are more stars, and if more brightness appears in that section in which the stars are more numerous and closer together, it is reasonable that it is the multitude of stars that causes this appearance. What was said of the circle itself, and of the stars existing in it, can be seen from the diagram—since the astronomers have drawn charts of the whole sphere and of the constellations in it. 91. Exponit autem consequenter quare stellae in circulo lacteo existentes vocantur sporadicae, idest seminatae: quia videlicet sic sunt dispersae per illam partem caeli, quod non contingit eas ordinare sub aliqua figuratione, sicut stellas existentes in aliis partibus caeli; quia unaquaeque earum non habet aliquam determinatam positionem, ut possit ad similitudinem alicuius figurae reduci. Et hoc manifestum est aspicienti in caelo: quia in solo hoc circulo spatia intermedia inter stellas maiores, sunt plena quibusdam parvis stellis; sed in aliis locis caeli manifeste deficiunt stellae, quapropter intermedia apparent vacua a stellis. 91. Then he explains why the stars in the milky circle are called sporadic, i.e., scattered like seeds: it is because they are scattered through that region of the heaven in such a way that they do not allow being grouped under some figure as do the stars existing in other regions of the heaven, since each of them does not have a fixed position so that they could be reduced into the likeness of some figure. This is plain to anyone looking at the heaven: because it is only in this circle that the areas between the major stars are filled with certain small stars; while in other regions of the heaven stars are manifestly lacking, so that the intervening spaces appear empty of stars. 92. Deinde cum dicit: quare si quidem etc., concludit ex supradictis suam intentionem. Et dicit quod si causa supra assignata de apparitione cometae, acceptanda est tanquam mediocriter dicta (quia scilicet nullum habet inconveniens manifestum), existimandum est etiam sic se habere de circulo lacteo: quia quod in cometis est coma circa unam stellam, eandem passionem accidit fieri circa quendam circulum. Ita quod lactea claritas, ut ita dicatur quasi definiendo, nihil aliud sit (lactea via) quam coma eiusdem maximi circuli, in caelo apparens propter segregationem, idest elevationem a terra, exhalationis ad illam partem adunatae. Et ideo, sicut prius dictum est, non fiunt multi cometae neque frequenter, quia talis adunatio exhalationis quae elevata est a terra, elevatur secundum unamquamque circulationem, et adunatur maxime in loco lactei circuli; ita quod a lacteo circulo exhalatio superabundans non relinquitur, quae possit esse materia apta ad cometae apparitionem. 92. Then when he says, hence if (346b1), he concludes his intention from the foregoing. And he says that if the cause assigned above of the comet's appearance is accepted as plausible (because it involves no manifest inconsistencies), the same should be accorded this explanation of the milky circle: because what, in the case of comets, is a fringe about one star, is here a corresponding passion affecting some one circle. Thus, the milky clarity, if one were, so to speak, to define it, would be, as the milky way, nothing other than a fringe [coma] of the same greatest circle, appearing in the heaven on account of the separating, i.e., the lifting from the earth, of an exhalation concentrated in that area. And therefore, as was already stated, many comets are not produced and they do not appear frequently, since such a gathering of the exhalation elevated from the earth is drawn up in accord with each revolution and brought together mostly in the region of the milky circle, in such a way that no surplus exhalation is left over from the milky circle which could be material suitable for the appearance of a comet. 93. Ultimo autem recapitulat ea quae dicta sunt. Et dicit quod dictum est de his quae fiunt in hoc mundo qui est circa terram, qui scilicet est suppositus generationi et corruptioni, quantum ad illum locum qui est continuus, idest contiguus, motibus caelestibus: scilicet de discursu astrorum, et de ignita flamma, et de cometis et lacteo circulo; quia huiusmodi passiones apparent circa locum istum superiorem. 93. Finally he sums up what has been said and says that we have spoken of the things that take place in the earth-environing world, which is subject, namely, to generation and corruption, as to that region which is continuous (346b10), i.e., contiguous, to the heavenly movements: of the shooting of stars and of the burning flame and of comets and the milky circle, because such passions appear in that upper region. Lectio 14 Lecture 14 De causis in communi illorum meteorum quae ex humida echalatione generantur in inferiori parte aeris—de pluvia, rore et pruina The causes in general of phenomena generated by the moist exhalation in the lower part of the air. Of rain, dew and frost. De loco autem positione secundo post hunc, primo autem circa terram, dicamus. Iste enim locus communis est aquae et aeris, et accidentium circa eam quae sursum generationem ipsius. Sumendum autem et horum principia et causas omnium similiter. Let us go on to treat of the region which follows next in order after this and which immediately surrounds the earth. It is the region common to water and air, and the processes attending the formation of water above take place in it. We must consider the principles and causes of all these phenomena too as before. Quod quidem igitur ut movens et principale et primum principiorum, circulus est, in quo manifeste solis latio disgregans et congregans, in fieri prope aut longius, causa generationis et corruptionis est. The efficient and chief and first cause is the circle in which the sun moves. For the sun as it approaches or recedes, obviously causes dissipation and condensation and so gives rise to generation and destruction. Manente autem terra, quod circa ipsam humidum, a radiis et ab alia quae desuper caliditate evaporans , sursum fertur. Now the earth remains but the moisture surrounding it is made to evaporate by the sun's rays and the other heat from above, and rises. Caliditate autem quae duxit sursum, relinquente, et hac quidem directa ad superiorem locum, hac autem et extincta propter suspendi longius in aere qui super terram, constat iterum vapor infrigidatus et propter derelictionem caloris et propter locum, et fit aqua ex aere; facta autem, iterum fertur ad terram. But when the heat which was raising it leaves it, in part dispersing to the higher region, in part quenched through rising so far into the upper air, then the vapor cools because its heat is gone and because the place is cold, and condenses again and turns from air into water. And after the water has formed it falls down again to the earth. Est autem quae quidem ex aqua exhalatio, vapor; quae autem ex aere in aquam, nubes; caligo autem nebulae, decidentia eius quae in aquam concretionis. Propter quod signum magis est serenitatis quam aquarum: est enim caligo velut nebula sterilis. The exhalation of water is vapor: air condensing into water is cloud. Mist is what is left over when a cloud condenses into water, and is therefore rather a sign of fine weather than of rain; for mist might be called a barren cloud. Fit autem circulus iste imitans solis circulum: simul enim ille ad plagas permutatur, et iste sursum et deorsum. Oportet autem intelligere hunc velut fluvium fluentem circulum, sursum et deorsum, communem aeris et aquae: prope quidem enim existente sole, vaporis sursum fluit fluvius; elongato autem, aquae deorsum; et hoc indesinens vult fieri secundum ordinem. Quare, siquidem aenigmatizabant Oceanum priores, forte utique hunc fluvium dicebant circulariter fluentem circa terram. So we get a circular process that follows the course of the sun. For according as the sun moves to this side or that, the moisture in this process rises or falls. We must think of it as a river flowing up and down in a circle and made up partly of air, partly of water. When the sun is near, the stream of vapor flows upwards; when it recedes, the stream of water flows down: and the order of sequence, at all events, in this process always remains the same. So if 'Oceanus' had some secret meaning in early writers, perhaps they may have meant this river that flows in a circle about the earth. Elevato autem humido semper propter calidi virtutem, et iterum lato deorsum propter infrigidationem ad terram, proprie nomina passionibus imponuntur ex quibusdam differentiis ipsarum. Cum quidem enim secundum modica feratur, psecades; quando autem secundum maiores partes, pluvia vocatur. So the moisture is always raised by the heat and descends to the earth again when it gets cold. These processes and, in some cases, their varieties are distinguished by special names. When the water falls in small drops it is called a drizzle; when the drops are larger it is rain. Ex eo autem quod de die evaporat, quantum non suspensum fuerit, propter paucitatem sursum ducentis ipsum ignis ad eam quae elevatur aquam, iterum deorsum latum, cura infrigidatum fuerit nocte, vocatur ros et pruina: Some of the vapor that is formed by day does not rise high because the ratio of the fire that is raising it to the water that is being raised is small. When this cools and descends at night it is called dew and hoar-frost. 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.