3. Three books precede the present one, according to order, in natural science. Hence he does three things [1].

First, he states what was treated in the book of Physics. As to the first two books, it is question of the causes of nature. This he alludes to, concluding from what has been determined in the books preceding [The Meteorology], when he says: "We have already spoken about the first causes of nature," meaning by "first causes of nature," the first principles, which are matter, form and privation, as well as the four genera of causes, namely, matter, form, agent and end. In the subsequent books of the Physics the discussion is of motion in general; hence he adds, "and of every natural motion."

The second book of natural science is the book, On the Heavens, in the first part of which, i.e., in its first two books, the discussion is about the heaven and the stars, which are moved with circular motion. This he alludes to when he says: "We have also discussed the superior movement of the well-appointed stars," meaning by "well-appointed," very beautifully arranged, and by "as to their superior motion," the circular motion by which all the heavenly bodies are moved. In the second part of that book, i.e. in the third and fourth books, he determines concerning the number of elements and their local motion. Alluding to this he says: "and about the bodily elements we have discussed their number and nature." He says "bodily" elemnets to distinguish them from the first principles, namely, matterand form, which are not bodies but the ele4ments or principles of bodies, whereas fire and water and earth are bodies, and are the elements of other bodies.

The third book of natural science is the book, On Generation, wherein are treated the mutual transmutation of elements, in the second book; and generation and corruption in common, in the first book. This he subsequently alludes to when he says: "and of things that are mutually transmutable."

4. Then [2] he shows what is to be discussed in the present book. About this he does two things:

He says therefore first that the remaining part of "this method," i.e. of natural science, which we have before us, is still to be treated. [What is now to be considered] is what all the earlier philosophers called "meteorology" - from meteoron which means "on high" or "elevated," and from logos, which is a "statement" or "explanation" - for in it are considered the things generated on high, such as falling stars, comets, rain, snow, and so on. This does not mean that other things, produced in the lower regions, such as lightning, earthquakes and the like, will not be discussed; but, because things generated on high are more marvelous and more desired, it is from them that this whole doctrine takes its name.

5. Secondly [3] he enumerates the things to be considered in this doctrine. These are seen to be divided into four groups. For there are some things that are produced in the highest region, nearest to the heavenly body. Such things are, namely, those concerning which it still remains to be considered, things that happen indeed according to nature, but not an ordered nature and, as some claimed, by chance. This moreirregular nature is not, however, the nature which belongs to the "first element of bodies," i.e., the celestial body, called "element," because it is a part of the whole corporeal univese, although it does not enter int othe composition of mixed bodies, as do the elements. The nature according to which these things occur is more unordered than the nature of the celestial body, since the things in the celestial body always behave in the same way, whereas in the transmutations affectingthe lower bodies much variation occurs. It was on this account that some have believed that these occurred, not by nature, but by chance, failing to consider that there isproduced by nature, not only those things which happen always, but also those which happen for the most part. These, I say, occur in the region nearest the "carrying of the stars," i.e., the stars that are circularly moved. This he sets down to distinguish them from those that follow. As an example he mentions the "Milk," i.e., the milky circle called the "galaxy," and the stars called "comets," and the "phantoms," i.e. the apparitions, fiery and moving, called "falling stars" [meteors].

6. Secondly [4], he enumerates the things which take place under the foregoing; namely, all things that are posited as phenomena common to air and water - for they are produced from aqueous matter in the region of air, when vapors are changed into water.

7. Thirdly [5], he enumerates what takes place in the lowest region and says: "We must also talk about the parts of the earth," such as east, west, north, south, "and about its kinds," for example, that some earth is hot and sandy, and some cold and compact, "and about the properties of the parts" of the earth, for example, that some are sulphurous, some stony or in some way broken up. "From this knowledge" of the earth "we shall consider all the causes of "spirits," i.e., winds, that differ according to the difference of the earth. Likewise, "of earthquakes," the causes of which are attributed to the different type of earth, "and of all things that take place according to the motions of these," i.e., of winds and earthquakes. In these matters we cannot explain everything perfectly and according to certitude, but shall let some things remain doubtful, giving reasons for both sides; but in others we shall to some degree reach the truth.

8. Fourthly [6], he enumerates the things which descend from on high as the result of winds. He says, therefore, that we shall also give an account of the falling of thunderbolts, and of whirlwinds (called "siphons") and of the burnings that accompany such whirlwinds, and of other circular phenomena that occur from congealing and are properties of those bodies, namely, the elements. He says this because whirlwinds are generated from compacted matter set rotating, and many other like things happen to whirlwinds as a result of matter compacted and set in circular motion. Or this could refer to the rainbow and halo (i.e., the corona surrounding the sun and moon and stars) which result from rays rebounding from thick matter.

9. Then at [7] he mentions what remains to be treated in the books to follow and says that after we shall have finished with these matters enumerated above, we shall to the best of our ability, according to the method employed in earlier books (i.e., not by merely reciting others' opinions, but by inquiring into causes, speculate about animals and plants, both in a universal way and according to the individual species. And that will be almost the end of the natural science which we chose to discuss from the beginning. He says "almost," because not all natural things can be known by man.

About the first he does two things:

11. He says therefore first [8] that it has been previously determined both in the book, On the Heavens, and in the book, On Generation, that among the other corporeal principles that are principles of other bodies there is one which is the principle of those bodies from which is constituted the nature of the bodies circularly moved, i.e., of spheres and stars. This principle, out of which all such bodies are formed, he calls the "fifth essence." The other principles, of the lower bodies, are four in number, because of the primary tangible qualities, which are the principles of acting and of being acted upon. These are the hot, cold, moist and dry, of which there are but four possible combinations: for the hot and dry is fire, the hot and moist is air, the cold and moist is water, and the cold and dry is earth (that something should be hot and cold, or moist and dry, is impossible).

Of these four bodies there are two motions: one is upward from the middle [center] of the world, and this is the motion of light things, namely, fire and air; the other is to the middle [center], and this is the motion of heavy things, namely, earth and water. Accordingly, bodily motions are threefold: namely, to the middle for heavy bodies; from the middle for light bodies; and about the middle for the heavenly bodies, which are neither heavy nor light.

But notice should be taken of the differences in light and heavy. For there is something which is absolutely light, namely, fire, which is above all the others; there is something which is absolutely heavy, namely, earth, which is under all the others. But the other two are in a certain respect heavy and light — for air is light in relation to earth and water, but heavy in relation to fire; water, on the other hand, is light with respect to earth, but heavy with respect to air and fire. Consequently, these two are proportional to the other two that are extremes, i.e., as air is nearer to fire, so water is nearer to earth. Thus it is plain that the universe around the earth consists of four bodies. This is the world chose passions — which are the various transmutations found in the elements — we must consider in this book.

12. Then [9] he shows how the aforesaid principles are related to one another in causing. And he says that it is necessary for the lower world to consist of the four elements thus in continuity with the "upper movements," i.e., with the bodies circularly moved (by "continuous" he here means "contiguous," in the sense that nothing lies between them). The reason why this is necessary is not only because no empty place can exist (hence bodies must be contiguous to bodies), but also because the end requires it — the end being that the whole power of the lower world be governed by the superior bodies, and this would not be, unless they touched — for a bodily agent must touch the thing acted upon and moved by it.

13. That the lower world is ruled and moved by the superior bodies he proves with two arguments. The first is this: The movent cause, i.e., the originative principle of motion, is necessarily the first cause. (This is to be understood in its relation to the formal and material cause. For matter is acted upon by the agent, which is by nature prior to the patient. The form, too, is an effect of the movent, which educes matter from potency to act. But the end is prior to the agent, because it moves the agent. Yet it is not always prior in the order of existence, but [sometimes] only in the order of intention.) Now it is plain that in the sphere of natural things the heavenly body is the first cause, and this is proved from its incorruptibility and nobility. Consequently, the heavenly body, with respect to these lower bodies, must be the originative cause of motion.

14. At [10] he gives the second argument, which is this: The motion of the heavenly body is perpetual. This is apparent from the very disposition of place: for in the case of a straight line, one arrives at an end in act, namely, the terminus of the line, but in the case of a circle, one does not arrive at an end. He says, therefore, that circular motion does not have an end according to place. And lest anyone conclude from this that circular motion is imperfect, on the same ground that a straight motion is imperfect before reaching its end, he adds that a circular motion is always at an end — for any point you designate on a circle is both a beginning and an end, and circular motion is as perfect at any sector as a straight motion is at its end. Therefore it is plain, from the very disposition of place, that, to heavenly motions, perpetuity is congruent.

The motions of lower bodies, on the other hand, cannot be perpetual, because such bodies are moved with rectilinear motions, and a rectilinear motion remains one and continuous only according to the measure of the rectilinear magnitude along which the motion passes, and a reflected motion is not continuous, as was proved in Physics VIII. Hence, since all the lower bodies are a finite distance from one another, and no such body is infinite, as was proved in Physics III and in On the Heavens I, their motions must be finite and not perpetual. What is perpetual and always, consequently, is the movent of those things which are not always. Wherefore the lower elements, namely, fire and earth and the others which are "syngeneous," i.e., congenerable, with them, namely, air and water, and those things which are composed out of them, must be reckoned the causes of the things occurring in the lower world, "in the line of matter," i.e., after the manner of the material cause, because that is the way we speak of a subject and a patient being a cause of things. But their cause in the sense of "originative source of motion," i.e., their cause after the manner of movent cause, must be "sustained," i.e., held, to be that power which belongs to the "always moved," i.e., to the heavenly bodies, which are always in motion — for what is always in motion is compared to what is not forever in motion as agent is compared to patient.

The first part is divided into two parts:

The first part is divided into three parts:

He says therefore first [11] that we must speak of the "image of the milk," i.e., of the appearance of the milky circle, and of comets and of all other like things which are "syngeneous," i.e., generable along with them; but in doing so we shall [first] recall the positions laid down by us in the earlier books and the determinations already determined therein, so that we may, when necessary, use them to manifest the proposition.

16. Then [12] he sets forth certain things needed for what is to follow. About this he does two things:

He says therefore first [12] that fire and air and water and earth are produced from one another (even though Empedocles thought the contrary). And he restates this as proved in On Generation II. The reason for this which he assigns is that each element exists potentially in another, and that things so related can be generated one from the other. He assigns a further reason, which is that they all have the same common first matter which underlies each of them and into which, as into an ultimate, they are all resolved: for all things whose matter is one and common to all are so related that any one is potentially in any other — as, for example, a knife is potentially in a nail, and a nail potentially in a knife, because they have a common matter, iron.

17. Then [13] he inquires into the order of the elements and into the case of air in particular. About this he does three things:

First he raises the question and says that our first problem is about the body called "air," as to what nature it has in the world surrounding the earth: i.e., is the whole air, and, if not, how it is related to the other elements?

Secondly [14], he proposes certain evident facts about the order of the elements. The first fact concerns the earth, and it is that we are not entirely ignorant of the size of the earth in comparison to the surrounding magnitudes, namely, those of the heavenly bodies and of the other elements. For it is already plain from the considerations of astronomers that the earth is much smaller than certain stars, and that it is but the size of a point in comparison to the outermost sphere.

The second fact he proposes is about water [15] and he says that we do not observe water to exist by itself and isolated from the body located about the earth, namely, from the sea and rivers, which we see, and from the bodies of water which some have asserted to exist hidden from us in the bowels of the earth. For it does not occur to water to be gathered together in this way — since the moistness which is water is contained by some alien terminus.

18. He further [16] pursues the question he raised earlier, namely, as to what is the middle between the aforesaid [i.e., the earth and the farthest stars].

About this he does two things:

Regarding the first he proceeds thus. First [16] he says that there is a problem whether between earth and the farthest stars, which are called "non-wandering" and "fixed," we should posit, according to what is proper to nature, one body or more than one; and if more than one, how many, and where are the boundaries of their regions?

19. Secondly [17], he repeats something already determined in On the Heavens: this is the condition, as far as its power is concerned, of the first element, namely, the celestial body; and that that entire world which is "about the upper motions," i.e., which is moved with a circular motion, is filled with that body — for all the heavenly bodies pertain to the nature of that first element. And since the philosophers supposed the contrary, he therefore, lest his opinion appear novel, adds that not only did he have this opinion, but it was also an ancient opinion of earlier men. For the body which is called "aether," and which we call the "heaven," has an ancient name.

But Anaxagoras seems to have supposed that it means the same as "fire" - for he took the word "aether" not to mean "always running," i.e., to be in continuous motion, but he derives it from aethein, which is "to burn," because he believed the superior bodies to be filled with fire. And although in this he spoke ill, nevertheless he was right in supposing the name "aether" to befit a corporeal potency over and above those bodies. For all the ancients are seen to have believed, and decided, that the name "aether" should be given to the body which always "runs," i.e., is always in motion, and which is a certain "divine," i.e., perpetual, something according to its nature. This they did as if that body were like no body that exists around us. Nor should it seem strange if this opinion, which we appeared to have adopted for the first time, was already held by the ancients. For we hold that the same opinions re-appear among men after dying out through neglect of study, not twice or thrice only, but an infinitude of times. Now he says this in keeping with his opinion that the world and human generation have been going on from eternity, as indicated in previous books. This being supposed, it is also plain that certain opinions and arts have begun from certain definite times; and thus it is necessary to say that these were in turn frequently, nay, an infinitude of times, destroyed by wars or other corrupting factors and again rediscovered.

20. Thirdly [18], he shows that the circularly moved body is not any of the lower bodies. About this he does three things:

With respect to the first [l8] it should be kept in mind that some have thought only the "carried" [moved] heavenly bodies, i.e., the sun, moon and stars, to have a fiery nature, and whatever exists between them to be of the nature of air; some on the other hand supposed the entire system to be of the nature of fire, as Anaxagoras said.

He says therefore that those who posited not only the moving bodies to be pure fire, but also the whole that surrounds them (i.e., all the spheres), and that which intervenes between earth and the stars to be air, i.e., from the earth to the moon's orb, and that whatever is above is all of it fire — whoever, I say, claim this, would, were they to consider the facts which have now been sufficiently proved by the mathematicians concerning the sizes of bodies, probably give up this childish opinion. Only a simple and unschooled person would believe that the stars are small in size just because they appear small to us looking at them from afar.

This matter has been already discussed in the previous reasonings, i.e., in On the Heavens II; but we shall once more destroy the aforesaid position with the same argument. For, since the bodies of the stars and spheres are immeasurably greater than the size of the earth and of the things near the earth, then, if not only the bodies of the stars were of fire, but all the area between them were full of fire, every one of the elements would have long since been annihilated by virtue of the preponderance of fire over it.

21. Then [19] he shows the same thing with respect to both. About this he does two things:

He says therefore first [20] that the due proportion among the elements is not kept, if the entire space between the earth and the outermost heaven is full of two elements, namely, fire and air. For the bulk of the earth, in which the whole quantity of water is also contained, is as no part at all compared to the total size of the bodies surrounding it, since, according to astronomers, even if compared only to the outermost sphere, it is as a mere point. But we see that when, as a result of separation or rarefaction, air comes to be from water, or fire from air, there is not such an immense excess in size. Now it is necessary, if the due proportion prevailing among the elements is to be preserved, that this small quantity of water maintain the same "reason," i.e., proportion, to the air made from it, as is maintained between the whole of water and the whole of air. In other words, the extent to which the quantity of air exceeds the quantity of water from which it is made must be proportional to the extent that all the air in the world exceeds all the water in the world.

22. Then [21] he refutes a certain cavilling objection and says that it is nothing against our position if someone should maintain, according to the opinion of Enpedocles, that the elements are not generated from one another. For it is necessary, according to his opinion, that the elements be proportionally equal in power. Consequently, proportionate equality of power must be kept in the sizes of the elements if they are not generated one from the other, just as if they are.

23. Then he summarizes [22] what has been said, and concludes that it is plain from the foregoing that neither does air fill the intermediate place between the earth and the highest stars, nor does fire; but, in addition to these two elements, there must be above them a heavenly body which is none of the lower elements.

The first is divided into three parts, according to the three questions raised:

He says therefore first [23] 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. Then [24] 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. Then [25] 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. 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. 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 cf the stars to prevent the thickening of clouds. 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 neer 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.

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. 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. 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." 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. 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. Then at [26] he solves the questions proposed:

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. Secondly, at [27] 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. 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. 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.

28 bis. Thirdly [28] 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.

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. For the elements are arranged in a manner that befits their nature; therefore, beeause 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.

The first is divided into two parts, according to the two causes assigned; The second begins at 36.

With respect to the first he does three things. First [33] he assigns the cause on account of which heat is generated in these lower bodies by heavenly bodies not themselves hot. And he says that by sense observation we see that movement, since it can separate and rarefy air, can also inflame it: for rarity and combustion go hand in hand, just as do cooling and thickening; and on this account, things borne along, such as arrows, if they include lead and wax, are often seen to melt, as though motion were making them hot. Hence it is not inconceivable that the heaven, by its motion, should heat these lower bodies.

34. Secondly [34], he assigns the cause why heat is caused in these lower bodies more by the motion of the sun than by the motion of some other superior body. And he says that the sun by itself suffices to produce a burning heat in these lower bodies: for the heat produced from other heavenly bodies is almost imperceptible when compared to the heat caused by the sun. The reason for this is that if a motion is to cause vehement heat it must be rapid and close to us. Now the motions, both of the fixed stars, and of the five wandering stars [planets], which are, according to Aristotle, above the sun, namely, Saturn, Jupiter, Mars, Venus and Mercury, are indeed rapid, but they are far from us; on the other hand, the motion of the moon, although it is near, is, however, slow. But the motion of the sun has both, i.e., speed and nearness, in a manner sufficient to cause heat in these lower bodies.

What is said here about the velocity of the sun's motion is to be referred to its diurnal motion and not to the proper motions of the stars. For it is plain that all the stars complete their diurnal motion during the same period of time: but the closer a heavenly body is to the center, the smaller is the circumference of its orbit and the slower is it moved. But with respect to proper motions, the moon is moved most rapidly.

35. Thirdly [35] he assigns the cause why heat is generated more by the motion of the body of the sun than by the motion of its sphere. And he says that it is reasonable for heat to be produced more by the solar body itself. Something akin to this can be discerned from what happens where we are [on earth]: for here also the air close to thick objects being moved along through violence becomes very hot. And it is reasonable that this should happen: because it is especially the motion of a solid body that dissolves air; hence, since the solar body is more solid than the other parts of its sphere, since it is not diaphanous, heat is generated more from its motion than from the motion of its sphere. This, therefore, explains why heat from the sun reaches this place, even though the sun itself is not hot.

Nor is any obstacle to this cause offered by the presence between us and the sun of the moon which cannot become hot; for although it is not heated by the sun, it is nevertheless influenced in a certain manner by the sun, for we observe that it is illuminated by the sun. Yet a medium and an extreme are not always changed with the same species of change: thus a ray of the sun does not ignite a [magnifying] glass filled with water, but the piece of flax placed beyond.

Also the reason is apparent why, where a shadow is, there is not as much heat as in a place where the sun's rays strike: it is because a shadow is caused by a body blocking the sun and interrupting the continuing transmutation deriving from the sun; however, the action of the sun does reach the place where a shadow is by a sort of reflexion.

Nor should it be supposed that the sun's motion, as motion only, causes heat; rather, it is in so far as it is the motion of such a body, i.e., of a body having in its nature the power to cause heat. For all the forms of the lower bodies are reduced back to the heavenly bodies as to certain principles: that is why diverse heavenly bodies produce diverse effects in bodily things, not only so far as heat is considered, but as far as other passions and forms are concerned.

36. Then [36] he presents a proper cause of heat generated from the motion of the sun: yet not the universal cause but a particular cause. Hence he says that the fire which surrounds the lower parts of the world as a result of a heavenly body's motion is often violently thrust downwards and scattered through the air: because, as was said above, the upper part of the air and fire have a flow on account of the motion of the heaven.

37. Then [37] he shows something which the question supposed, namely, that heavenly-bodies are not hot or fiery; this he does by two signs. The first is that in that region we do not see the paths of those stars which seem to be falling [i.e., shooting stars], which are generated by combustion in the lower regions. This would not be the case if heavenly bodies were hot and fiery, because, wherever there is a greater and speedier motion, there something is ignited more readily.

The second sign is that the sun, which especially seems to be hot, considering its effects, is seen to be of a white, and not a fiery, color.

The first is divided into three parts:

About the first he does two things:

About the first he does two things:

First, he states his intention [38] and says that, having determined the foregoing, we must explain the cause of the appearance in the heaven of burning flames and of shooting stars and of so-called dali, i.e., torches, and aeges, i.e., goats. They will be discussed at one and the same time, because they are all alike in kind and produced by the same cause, and differ only in degree, as will be clear below.

39. Secondly [39], he determines his proposition, about which he does two things:

First, he states the causes generating the aforesaid, and says that the principle, both active and passive, of the aforesaid phenomena and of many others is what he will indicate. For when the earth has been warmed by the sun's motion, a certain exhalation is necessarily released from the earth. This is not of one sort, as some think, but is twofold: one is more vaporous and moist, the other more foam-like and dry — for from the aqueous moisture upon the earth's surface there is released and lifted on high a vaporous exhalation which is moist; from the earth itself, which is by nature dry, there is raised a fume-ike or foam-like exhalation. Of these, the foam-like exhalation rises above the other on account of warmth which dominates in it and renders it more subtle: for the dry and warm is light — and fire is of this nature. But the vaporous exhalation, which is more moist, finds its place under the foam-like, being heavier, for it is not so fine: hot and moist pertain to the nature of the air, which is below fire, which is hot and dry.

The very order of the elements surrounding the earth attests to this. For under the circular motion of the heaven there is first located what is hot and dry and which is commonly called "fire," though that is not its proper name, as has been said above: for, since the item common to every smoky exhalation has no name, and such is especially apt to burn, consequently, it was necessary to use words in keeping, and so such a fume-like evaporation comes to be called "fire." Under this fume-like exhalation is air. Thus we have posited both th eeffective cause of the aforesaid passions, which is the sun's movement, and the material cause, namely, the fume-like exhalation.

40. Secondly [40], he determines concerning the generation of the aforesaid passions. About this he does two things:

About the first he does three things:

He says therefore first [40] that, in the light of the foregoing, we must understand what we have just now called "fire" to be as a certain "fuel," i.e., a combustible material, and that it is situated in the sphericity which is about the earth in the last place (beginning, that is, from the earth), Hence, on account of its proximity to the heavenly motion it often bursts into flame, being heated when only "slightly moved," i.e., when slightly stirred by the motion of the body above it, as happens in the case of smoke, when it is ignited and becomes flame: for a flame is nothing but the burning of a dry "spirit," i.e., smoke. Therefore the ignition of the above-mentioned fuel, commonly speaking, is responsible for the generation of the aforesaid passions, when matter which is prepared is placed in the proximity of the efficient cause.

41. Then [41] he explains the differences among the aforesaid passions. About this he does two things:

First he shows what is the basis for the difference. And he says that from whatever source the aforesaid matter is had (regardless of how this "consistency" is obtained, namely, the aforesaid matter for burning), and when it is most perfectly disposed to be ignited, then it is so ignited in such a way by heating from the circular motion of the heaven: and the ignited passion varies according to the position and amount of the aforesaid matter.

42. Secondly [42], he determines the differences among the aforesaid passions. And he says that if the aforesaid matter has great width and length, there appears to be a certain flame enkindled in the heaven, similar to stubble burning in a field [area]. But if it does not have great width, but only length, then "dali," i.e., torches, and "aeges," i.e., goats, and shooting stars are generated and appear there. For if the aforesaid matter is more in length than in width, and when it burns, the fire "scintillates," i.e., seems to leap and run about like "aeges," i.e., goats (which happens because not all the matter begins to be ignited at once but according to certain small sections, beginning from some starting-point in the matter), when, I say, this happens, it is called "aeges," i.e., a goat. But when the burning of the aforesaid matter takes place without the aforesaid passion, i.e., without scintillation, because the entire material is ignited at once, then it is called a "dalus," i.e., a torch.

However, when the exhalation is not continuous, but frequent, and scattered in small areas, and in many ways, both according to length and according to width and even depth, then appear stars that seem to fly, because the material is rapidly consumed and ceased to be where it was previously burning, as happens with flax, if a small amount of it is laid down lengthwise and ignited: for the combustion seems to run along and seems similar to the movement of some fiery body.

In this way, it is therefore plain that the burning flame has most material; a medium amount what are called "torches" and "goats," and least for shooting stars, which accounts for their rather frequent occurrence.

43, But because shooting stars have an additional cause of their generation, he adds that sometimes an exhalation ignited by the sun's movement generates them, but sometimes, too, when cold causes air to thicken, that which is hot within, being thickened, is forced out downward and is separated from the cold; this causes the thickened mass to ignite and a falling star is seen. That is also why the motion of stars falling in that way is not assimilated to a burning, but rather to a projecting.

He says therefore first that, depending on the different position of the exhalation with respect to the sides or depth [i.e., top or bottom], the falling star will be moved differently — either above or below, or to the side, of its point of ejection by the cold. For if the condensed cold matter which does the ejecting has come together above, the falling star is moved downward by the expulsion; but if the matter has collected below, then it is moved upward; if it comes together in neither place, then its [the star's] motion is sideways, as though obliquely or along the diameter. And this often happens: for the ejected hot mass is moved with two motions: by nature, as hot, it is moved upwards; but through the violence of the ejection, it is moved downwards. But all such things, whose motions are so combined, are moved "according to the diameter," i.e., obliquely, since such a motion is as though a mean between ascent and descent. As a result the motion of falling stars is most often oblique.

Then he summarizes what has been set forth and says that the material cause of all the foregoing is an exhalation; but the movent cause is twofold: for sometimes it is the movement of a higher body, sometimes it is the condensing of air thickened by coldness, and subsequently forcing out the hot.

48. Then [47] he determines the place where the aforesaid are produced and says that they are all produced below the moon. A sign of this is that they appear to us to be moving very rapidly, as do things we project, such as arrows and the like, which, for being close to us, seem to be travelling faster than the stars and sun and moon — although it is plain that, in truth, the higher bodies are moved much faster than anything here.

About the first he does two things:

He says therefore first [49] that the causes of these apparitions and of the conflagrations discussed earlier are the same. For since it is plain that the upper air (which he earlier called "fuel") is so disposed as to be able to b eignited, so that sometimes a flame appears to burn, and sometimes it is ignited to give the appearance of moving torches and stars, it is not strange (since many varieties of ignitings occur in the air) that the upper air should appear colored with every variety of color.

For there are two ways in which air somewhat thickened comes to represent all varieties of colors: one way is when a feeble light, which is not enough to illuminate fully, shines through smoke or thick vapor; another way is when light is reflected off somewhat thickened air. From these two causes especially, there appears in the air a crimson and purple color, i.e., reddish and sub-red — for these colors appear especially when things fiery and white are mixed with black.

Such a mixture can occur as a result of the two above-mentioned causes: namely, by "superapposition" (described above as a feeble light shining through something fairly thick — as when the sun and the moon and other stars appear crimson when they rise and set, and as though sub-red when their light is not perfect). But I say this, if heat is present: because when it is cold, vapors are condensed and obscure the light of rising and setting stars more, so that it cannot get through; but when it is hot, the exhalations are finer and permit the light of the stars to pass through. Likewise, if the stars are seen through smoke, they have this color.

This mixture can also be produced by the other cause mentioned: namely, refraction, when the object from which the light is refracted (he here calls this object a "mirror"), whether it be a water-soaked cloud or something other of the same sort, is of such a nature as to reveal color but not shape. He will explain this, when it is question of the rainbow.

Then he explains why these colors quickly disappear and do not last long: it is because the cause of their appearance is "rapid,," i.e., quickly passes — for air does not maintain a given state very long, and becomes thick or fine very easily.

51. Then [50] he assigns the cause of "crevices" and "chasms" and says that when light visible in air is interrupted by something dark, due to thicker vapor than usual, depths and openings seem to exist in the heaven. A sign of this is that, when the vapor which interrupts the light becomes thicker still, fiery torches emerge or fall from these "crevices," as though something hot were ejected by the coldness which thickens the vapor. But when that dark vapor which interrupts the light becomes still more condensed and thick, it causes a greater depth to appear, because the white is overcome by black; when the situation is just the opposite, then only a crevice or opening appears.

It is plain, therefore, that both apparitions, i.e., that of colors and that of crevices, have a like cause, namely, black and white mixing together: but the purple or crimson color results from white shining through something black, whereas the crevices and chasms result from something black screening the white.

52. Then [51] he shows that many things of this sort occur but are not visible. And he says that white joined with black produces many varieties of color, as appears with flame in smoke, which produces various colors depending on whether the smoke is thick or fine. But by day the sun's brightness prevents these colors from being seen: at night, however, only red appears, because the other colors, such as green and other darker colors, are on account of their darkness like the color of night.

Finally, he sums up what has been determined and says [52] that these must be taken as the causes of shooting-stars and fire-stars and like apparitions "that make hasty appearances," i,e., that are seen to pass by without lasting very long.

The first is divided into two parts:

The first is divided into three parts according to the three opinions he presents.

54. First therefore [54], he gives the opinion of Anaxagoras and Democritus who said that comets are "symphases," i.e., co-appearances of [planets] the wandering stars. These are five in number (namely, Saturn, Jupiter, Mars, Venus and Mercury), some of which, as they approach one another seem to touch, and there seems to be one star, and "flowing hair" appears [the coma, hence "comet"], due to the increase of light.

55. He presents the second opinion [55], which was that of certain Pythagoreans living in Italy who said that a comet is one of the wandering stars [planets], but that the "phantasy," i.e., vision, of it occurs only after a long lapse of time, because it "exceeds," i.e., departs from the sun only slightly — as is the case with the star Mercury, which, because it only slightly "digresses from," i.e., moves away from, the sun, frequently does not appear, appearing only after a long time, having for a long time not appeared.

56. He presents the third opinion [56], which was that of certain followers of Hippocrates, and of Aeschylus, his disciple. This opinion is similar to the second in supposing that a comet is one of the wandering stars; it differs in that the second opinion held the wandering star had a tail [coma] of itself, whereas this third opinion holds that it does not have a tail of itself, but, since it is wandering, sometimes acquires a tail by its position. According to this opinion a certain moisture is attracted by the star, and, since they assume that vision occurs by a beholder emitting visual rays, they posited that a visual ray reaches that moisture attracted by the star and is then reflected toward the sun. In this way the attracted vapor acts as a certain fiery mirror for the sun (for things are visible in a mirror because of reflection); and they say that it is thus that the tail is formed.

57. Then he assigns the cause regulating the time of its appearance and says that a comet star "appears at greater intervals than the other stars," i.e., is rendered invisible longer than the other stars, because time-wise it is very slow in getting clear of the sun, i.e., only when it has completed its entire cycle. He calls this "being left behind": for the wandering stars are said to be "left behind" with respect to the first motion, either because they are moved in a contrary direction and thus seem to retreat by their own motion, or because, as some say, they are moved more slowly than the first heaven which in its diurnal motion revolves everything else. So they said that a comet star is left behind by the sun to the textent of the whole of its orbit; and therefore, when it returns to the point where it first began to recede, it appears once more and remains in view until it again gets in conjunction with the sun. They also said that this star moves away from the sun not only according to longitude, but also according to latitude, declining to the north and south winds, i.e., to the north and to the south.

58. He also assigns the cause regarding the place of this star's appearance. And he says that this star does not appear in between the two tropics, namely, of Cancer and Capricorn; for the sun travels through that portion of the heaven and consumes the moisture, so that in that portion of the heaven this star cannot attract any water. But when it shifts to the south, receding from the sun's course, it finds there an abundance of moisture, because it had not been consumed by the sun. But because of the obliquity of the horizon, for us who live in the north the part of its parallel circle which is above the earth is small, whereas the part below is larger; consequently, the sun which, at night, when comets are visible, is under the earth, is so far from the moisture attracted by the star that a man's vision cannot be reflected from the moisture to the sun — whether the sun is near the "tropic," namely, that of Capricorn, or whether it is in the "summer turnings," i.e., in the summer tropic, which is that of Cancer. For no matter where the sun is under the earth, its distance from the contracted vapor is too great for reflection, either from the circle or from the latitude of the zodiac. But when that star is left behind by the sun toward the "boreal" [north wind], i.e., the north, then it can acquire a tail — because there is there much moisture, and the circumference of its circle above the horizon is large there, whereas the part below is small. Consequently it is easy for man's reflected vision to reach the sun.

60. As to the first [58] he gives two arguments: the first of which is that all the wandering stars are "left behind," i.e., move as though being left behind, as already explained, in the "circle of animals called the "Zodiac"; on the other hand, many'comets are found outside this circle. Therefore, not all comets are wandering stars.

The second argument is this: more comets than one have often been seen together; hence a comet is not one of the wandering stars. The first of these arguments is against these opinions together; the second is specifically against the second and third opinions.

61. Then [59] he disproves the opinion of Hippocrates with three arguments. As to the first of these he says that if a planet has a tail because of the reflection of the sight, as Hippocrates said, then it would have occasionally to appear without a tail. This is because it does not everywhere have a tail, as was said, but only when it is outside the tropics, receding to the north — for it is plain that it "falls behind" in other places as though receding from the sun; consequently it must sometimes appear without a tail. But no star is seen wandering without a tail other than the above-mentioned five. But occasionally all five are visible above the horizon at the same time; and when all are above the horizon, or some appear above and some are with the sun, comets nevertheless appear. Hence it is plain that a comet is not always one of the five wandering stars. And there is no other without a tail than these [five]. Therefore a comet is not a wandering star, which on occasion appears with a tail — which would have to be the case, if it did not possess a tail of itself but from being in some determined place, as they claim.

62. He gives the second argument [60] and says that it is not true to say that a comet occurs only in the region toward the north with the additional observation of the sun at the summer tropics [i.e., summer solstice], as though nearer to the comet. For the great comet which appeared at the time of the great earthquake and tidal wave in Achaia arose from the western equator; so it is plain that it occurred within the "tropics." Moreover, many have appeared in the south. It is therefore false to say that they occur only toward the north.

63. He gives a third argument [61] and says that in the time of a certain Athenian ruler, a comet star was formed when the sun was near the winter tropics [solstice], i.e., near Capricorn and this was in the month of "Gamelion," i.e., December or January. Now as they themselves admit, it seems impossible for such a long reflection from our vision to the sun to occur, considering the distance to the sun then prevailing at night and considering the size of the section of the circle below the horizon. Therefore, their claim that a comet does not appear unless the sun is near the summer tropic [solstice] is false.

64. Then [62] he disproves the first opinion with four arguments. The first of these is against all the aforesaid opinions that claim the comets are wandering stars — for even certain stars that are not wandering receive a tail. And this is to be believed not only on the authority of certain Egyptians devoted to mathematics, but Aristotle himself says that he saw one of the stars in the constellation of the Dog, in the thigh, to be exact, with a tail, although it was faint: this was evidenced by the fact that when you gazed at it intently, the light of the tail grew dim, but when one glanced at the star not too intensely but more moderately, more of the tail's light appeared.

65. In the second argument [63] he says that all the comets that were seen in his time disappeared in a region above the horizon "without setting," i.e., without approaching the sun. For stars are said to "set" when they enter into the sun's rays; but the comets of his time disappeared without approaching the sun, still being above the horizon far from the sun. And they disappeared as if gradually wasting away without leaving behind the body of one star or of several. For the great star previously described, which was at the time of the earthquake in Achaia, in the Athenian archonship of Astius, appeared in winter during the evening when it was frosty and clear: on the first day, not the star, but only its tail, appeared, as though setting before the sun; but on the second day it was as visible as conditions permitted, because for a short time it remained behind the sun and then immediately set; but the light of that comet spread over a third part of the heaven which burst into light not gradually but all at once, so that the upward ascent of the light was called the comet's path; it did indeed ascend, receding from the sun toward the stars called "Orion's belt," where it was dissolved, not by approaching the sun, but by receding farther and farther from it.

This is also an argument against all the foregoing opinions that say a comet is one or more of the wandering stars. Consequently, it is plain from this argument that what Democritus said in support of his opinion was insufficient. For he said that when comets dissolved, there sometimes appeared certain remaining stars. This is an insufficient explanation because it devolved on him to prove that stars always, and not just occasionally, remained when comets were dissolved — which has been seen to be false from what has been said.

66. He gives a third argument [64] which is this: Egyptians claim that the conjunctions of the planets with one another and with certain fixed stars take place. And he says that he himself saw Jupiter conjoin with a star in Gemini and make it invisible. Yet no comet was formed, as should have according to the opinion of Democritus and Anaxagoras.

67. The fourth argument [65] is this: Although some stars seem to be larger and some smaller when compared to one another, yet each considered by itself appears to be as though a point and indivisible. But if they were in very truth indivisible, they could not produce a larger magnitude by merely touching one another, as was proved in Physics VI. Therefore, when they seem to be indivisibles, although they are not, they should not, when in conjunction, seem larger as far as their apparent size is concerned. Consequently, from the conjunction of stars a tail should not be visible as though produced by an increase of light. (These last two arguments are properly against Democritus' opinion). Finally, he summarizes what has been said — as is had in text [66].

The first is divided into two parts:

Regarding the first he does two things:

70. About the first he does three things: First [68], in order to manifest his proposition he re-introduces certain things already stated. And he says that we must maintain what has been said above to the effect that in the region of the lower world surrounding the earth, the first and highest part, below the bodies in circular motion, is the exhalation of the hot and dry. We must also suppose, as stated above, that this hot-dry exhalation, as well as a large portion of the air continuous with the fire, are revolved together around the earth, under the heavenly sphere, with a circular motion, as though carried and drawn along by the turning of the heaven. Thirdly, we must assume that the above-mentioned exhalation, thus moved, is frequently ignited in whatever way it happens to be disposed to allow fire to prevail well in it: this being, as was said, the cause of the shooing of certain stars.

71. Secondly [69], he assigns a cause for the appearance of a comet and says that when such an exhalation condenses and when, as a result of the higher body's-motion, a source of combustion falls into this exhalation and causes a flame to burst out in a certain area in such a way that the fire is neither large enough to consume all the material quickly, nor so weak as to quickly die out before a conflagration occurs, but such as to last more and for a long time, in keeping with the size of the fire and the disposition of the condensed matter; and when along with this there continually rises from below an exhalation well disposed for this type of burning, i.e., sufficient to keep it burning for a long time, then it is that comets are formed. — For the material already on fire appears to be a star, while the rest of the exhalation, which is not yet completely ignited but on the way to being ignited appears as a tail. The shape of the exhalation determines the shape that will appear: if the exhalation completely surrounds the "star," i.e., the origin or ignited part, there appears, as it were, a circle of tresses [coma], hence it is called "cometed"; but if it is disposed along the length of the ignited origin, then the exhalation appears as though the beard of the star, and is therefore said to be "pogoniated," i.e., bearded.

72. Thirdly [70], he explains what was said about a comet by comparison with a falling star. For it was said above that the motion of fire ignited in such material, when it is moved by ejection, seems to be the motion of a star; similarly, the tarrying or state of rest of the fiery principle in this matter seems to be the tarrying or state of rest of a star. He says that a comet star is at rest so as to exclude the motion which appears in falling stars, but not so as to exclude the comet's motion as it is revolved along with the heaven. He will speak of this later. The reason why the above-mentioned principle tarries is that the material is not consumed at once, owing to the amount and thickness of the material and to the weakness of the fire, as well as to the other material that replaces it, as has been said.

It is as though someone threw a torch or other burning source into a large pile of chaff: the fire does not at once travel as though consuming the chaff, but the igniting seems to remain in one area for a long time. From this example properly understood one can see that the shooting of falling stars has a certain likeness to the appearance of a comet. For in shooting stars the fire travels quickly along the length on account of the disposition, namely, in the fuel, that permits it to be easily burned; but if the flame were to tarry and not pass along by consuming the matter, or if the material were very dense, so as not to be swiftly consumed, then, as though the intermediate trajectory had been taken away, there would only be the star standing, as is the case in the beginning and end of the trajectory.

Such is the comet. Thus we can imagine a comet as though it were a shooting star, as such a star is at the beginning and end of its course but with no shooting motion. He therefore concludes that when the source of its consistency was "in a lower place," i.e., under the lunar globe, a comet is said to appear by itself, without being accompanied by any star, either wandering or fixed.

73. Then [71] he describes another way in which comets appear. And he says that when an exhalation is collected under some star, wandering or not wandering, on account of the motion of that star, then some such star becomes a comet — not that the star which appears is a fiery object in the air, as in the case cited above, but it is a true star, wandering or not wandering. Its "coma," however, does not come into existence in the heavenly region where the stars are, but under the heaven in the air.

And he gives the example of the "halo," i.e., of the air which sometimes is seen to surround the sun and moon, even though the sun and moon are in motion. Such a halo does not exist in the place where the sun and moon exist, though it accompany the sun and moon, even when the latter are moved. This passion comes into existence in the air condensed under the course of the sun and moon, as will be explained later. Therefore, just as a halo is to the sun and moon, so a "coma" is to the fixed stars and wanderers, whenever they appear with a "coma," which is a certain exhalation farther down, namely, in the upper region of the air, deriving from the motion of those stars. Yet there is this difference between a halo and a "coma": the color of a halo is not in the vapor itself but is something that results from reflection toward a cloud, as will be explained later; but the color associated with a "coma" is properly a color belonging to the fumid exhalations themselves.

74. Then at [72] he points out the difference between comets as appearing in these two ways. And he says that when the accumulation of an exhalation takes place in relation to a fixed or wandering star, it is necessary that there clearly appear in the comet the motion which belongs to the star to which the "coma" belongs; but when the comet star is fire existing per se in the air without any of the upper stars, then they seem to lag.

He explains this by the fact that the course of the lower world about the earth is such, namely, slower than the heavenly movement — for although fire and a large portion of the air are revolved by the motion of the firmament, they nevertheless cannot attain to the speed of the heavenly motion. Therefore the burning exhalation existing in the upper region of air is revolved along with the air and the fire. Because their motion is slower than that of the firmament, therefore the comet existing in the air remains behind the heavenly bodies, which are moving most rapidly. Consequently, from its slowness alone, it seems to have a movement contrary to the firmament, just as the planets do. Some indeed thought this of the planets — hence the aforesaid opinions posited that comets are planets.

But the very fact that a comet is often produced by itself, and this more frequently than in association with any of the "determinate," i.e., fixed, stars which have a fixed and determinate existence in the heaven, shows most plainly that a comet is not a reflexion produced in the exhalation (which he calls "hypeccauma" [fuel]) to the star to which the "coma" is attached, as is the case with a halo. But if it were as it is with a halo, the reflection of our vision would pass from the exhalation to the star, and not to the sun, as the followers of Hippocrates claim. But an account of the halo will be given later.

75. Then [73] he manifests what he had said, through a sign. And he says that an argument to show that the stuff of comets is fiery, or so far as the fringe [coma] appears, is that a number of comets is a herald of winds and droughts. For it is plain that winds and droughts are the result of much dry exhalation being drawn from the earth; as a result, the air is quite dry and the moisture which evaporates from the seas is rarified and dissolved by the abundance of hot exhalation; consequently, vapors are not easily condensed into water; rather, winds caused from the dry exhalations are generated. This will become clearer when winds are discussed. Thus, therefore, when frequent and numerous comets appear, which occurs as a result of the abundance of dry exhalation, the years are necessarily unusually dry and windy. But when the comets are less frequent, and not so large, the years are not notably dry and windy; yet frequently there is an excess of wind, either in duration because they last long, or in strength, because they blow furiously.

He gives examples. For sometimes a stone dropped into certain rivers from the air during the day, having been lifted by the wind; and then, that evening, a comet was formed. And the same is true of that large comet he referred to earlier: it was a dry winter with prevailing north winds, and because of contrary winds a tidal wave resulted and some cities are said to have been destroyed — for out on the sea a strong south wind was blowing, but in the bay a north wind prevailed. Likewise, under the rule of Nicomachus, a certain comet appeared and then a strong wind blew up in Corinth.

76. Then [74] he assigns the cause for the place and time of a comet's appearance. And he says that the reason why comets are few and infrequent and occur more often outside the "tropics," i.e., outside the sun's path, than within, is that the motion of the sun and stars not only releases the hot exhalations resolved from the earth, but also breaks up any consistency and thickness that might be in them. In this way the cause of a comet's appearing is hindered except in cases when there is a superabundant accumulation of such exhalations, which happens rarely. The main reason why comets appear rarely is that most of the matter which causes the appearance of comets is accumulated in the region of the milky circle, as will be said later: hence it is rarely that enough exhalation accumulates to account for the appearance both of a comet and of the "milky circle."

78. Regarding the first he does two things. First, he presents the opinion at [76] and says that some of the philosophers called "Pythagoreans" held that the milky circle is a certain path. But their opinions differed: for some asserted that it was the path of a certain star that passed through this part of the heaven after abandoning its own course when the heavens once went off the path — an event which the fables declare happened under Phaethon. Others say that the sun once travelled that path. Consequently, by the motion of the sun or of a star that area of the heaven was, so to speak, scorched, or affected in such a way that a patch of whiteness now appears there.

79. Secondly [77], he rejects this opinion and says that it is an inconsistency for those who posited this opinion that they did not at the same time see that, if the journey of the sun or a star were the cause of this brightness in this region of the heaven, such a disposition has much more reason for appearing in the circle of the Zodiac than in the milky circle — for not only the sun, but all the wandering stars move through the Zodiac. Now the whole zodiacal circle is visible to us, at different times, because at night half of it always appears above the earth (for the earth has the status of a point compared to the sphere of the fixed stars: hence earth's largeness does not conceal anything in the Zodiac from us); but although the entire Zodiac is visible to us, no such disposition appears in it, save in the region where it is joined with the milky circle.

80. Then [78] he presents the second opinion. First, he recites it and says that the followers of Anaxagoras and Democritus declared that the milky brightness which appears in the heaven is the light of certain stars. For when the sun is borne below the earth, they said, the earth's shadow reaches as far as the sphere of the fixed stars and covers some of them so that they do not receive the sun's rays; yet it does not cover all of them, because, due to the smallness of the earth, its shadow does not cover the entire heaven but only a small area. For they said that the brightness of the stars faced by the sun does not appear, because it is prevented from appearing by the sun's rays reaching them; consequently, no milky brightness surrounds them. But of the stars which the sun's rays do not reach, because the earth prevents this, their own light appears, which they identify as the milky brightness.

81. Secondly [79], he rejects this opinion for two reasons. In presenting the first of them he says that what it claims is impossible. For the milky brightness always appears in the same stars — the milky circle being seen to be one of the largest circles, which divide the sphere in half. But because the sun does not always remain in the same place in the heaven, other and other stars must always be being obscured from the sun's rays by the earth's shadow — since the shadow's motion must be imagined as opposite to the sun's course. Therefore, if the cause of the milky brightness' visibility were the earth's shadow blotting out the stars, then as the sun moved, the milky brightness would also have to shift. But this is not seen to happen, because it always appears in the same place and in the same stars, as was said. Consequently, the aforesaid theory is false.

82. He gives the second reason [80] and says that astronomical arguments and considerations prove that the sun is larger than earth and that the fixed stars are much farther from the earth than the sun is, just as the sun is farther from us than the moon is. Now when a shining body is larger than the opaque body whose interposition produces a shadow, the shadow does not increase indefinitely, rather it ascends in pyramid form to a cone of a certain quantity which is proportionately less as the shining body is less distant from the opaque one, and the more the former's size exceeds the latter's. Hence it is plain that the cone of the earth's shadow is not projected very far with respect to the rays coming from the sun; neither does the earth's shadow, which we call "night," reach as far as the fixed stars. What has to happen is that the sun has a view of all the fixed stars and that the earth blankets none of them. The reason why it blankets the moon and eclipses it is that the moon is lower than the sun, as has been said. Consequently, it is plain that the theory under discussion presupposed something false.

83. He presents the third opinion [81], and first he recites it, saying that there is a certain third theory about the milky circle. For some said that the milky brightness is due to our vision's being reflected from certain stars to the sun; as a result a brightness appeared around those stars striking our vision, so that they act as a certain mirror for the sun's brilliance, as Hippocrates also said when explaining the appearance of comets.

84. Secondly [82], he rejects this theory for two reasons. He sets down the first of these and says that the above opinion posits something impossible. And he lays down this proposition: If "everything," i.e., the entire system, namely, the beholder, the mirror, and the object seen by means of the mirror, all remain at rest, then of necessity the same part of the "emphaseos," i.e., of the form appearing, will appear "on the same sign of the mirror," i.e., at the same point at which the reflection of the visual line took place. But if the mirror should move, and likewise the object seen by means of the mirror, while the beholder remains at rest, and if the two things in motion always remain at thesame distance from the beholder, but with respect to one another are neither moving with equal speeds nor always at the same distance, then under these conditions it is impossible for the same appearance to occur in the same part of the mirror. For in practice it makes no difference whether the mirror and the thing seen are moving with unequal speeds, or one is in motion and the other at rest; and if this latter were the case, it is plain that the figure of the thing seen would appear now in one spot and now in another spot of the mirror, on account of the varying opposition according to position. And I say this, if the beholder is at rest: for if the beholder were to move, and the mirror remain at rest, while the object moved, then the figure of the thing seen could appear in the same spot on the mirror — since the beholder's motion could compensate for what was lacking due to the motion of the object seen, if they were thus proportionately moved. Hence, when the beholder remains at rest but the mirror and the thing seen are moved at unequal speeds, it is necessary that the figure not appear at the same spot on the mirror.

But the stars in the milky circle that are assumed to be a mirror, are in motion; moreover, there is motion of the sun, to which a reflection of our vision is assumed to take place'(the sun therefore plays the role of the thing seen); but we, the beholders, are at rest, because the earth is at rest (for the motion involved by our moving about on the earth makes no perceptible difference with respect to so great a size. Furthermore, the stars in question and the sun are equally moved in relation to us and their distance from us always remains the same. This does not mean that our distance from the sun is equal to our distance from the stars (for it has been previously said that the stars are higher than the sun), but that the sun, by its motion, does not increase or decrease its distance from us. And the same is true of a star. And by a "greater or less distance" is to be understood a distance that is significant with respect to the distance between the sun and the stars: we say this because of the smallness of the earth. But in relation to one another, the sun and the stars are not always equidistant: because "Delphis," i.e., the constellation of the Dolphin, which is in the milky circle, rises sometimes in the middle of the night and sometimes at dawn; and it is plain that this constellation is farther from the sun when it appears at night than when it appears at dawn. But the parts of the milky circle remain forever in the same place — which should not be the case if it were an appearance caused by a reflexion; for this brightness would not exist in the same place, as has been shown. Hence it is plain that the aforesaid theory is false.

85. He gives the second reason [83] and says that at night the form of the milky circle appears in water and other such mirror-like bodies. But it is inadmissible to say that in these cases vision is reflected by the water to the sun — in other words, considering the distances involved, it seems most unacceptable that there should be two reflections: one, namely, from the water to the milky circle, and another from the milky circle to the sun.

Finally, in summary he concludes that the milky circle is neither the path of any of the planets, as the first opinion held; nor the light of certain stars not regarded by the sun, as the second opinion said; nor the reverberation of our vision from the stars to the sun, as the third opinion maintained. And before his time these were the prevailing opinions about the "galaxy" [Milky Way].

He recalls two things: first, what was previously said about the location of the dry exhalation and of its kindling [85]. 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. Secondly [86], 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. Then [87] he manifests the proposition, showing what is the cause of the appearance of the milky circle. About this he does three things;

Regarding the first he does two things. First, he shows the cause of the appearance of the milky circle [87] 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. Secondly [88], 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. 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. Then [89] 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. 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. Then [90] 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. Finally he sums up what has been said [91] 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," 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.

95. Regarding the first he does two things: first, he shows what his intention concerns [92] 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. Secondly [93] he determines the proposition.

About the first he does three things: first, he sets down the efficient cause of these passions [93] 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. Secondly [94], 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. Thirdly [95], he shows the way in which the things under discussion are generated. About this he does three things: 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. Secondly [96] 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. Thirdly C97], 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. Then at [98] he discusses the foregoing passions in detail, by pointing out their mutual differences. And it is divided into two parts:

102. About the first he does two things: first, he determines about rain [98] 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," 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. Secondly [99], he determines about dew and frost. 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. Secondly [100], 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. Then [101] he shows the conditions of disposed air under which dew and frost occur.

About the first he does two things:

He says therefore first [101], 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.

106. Then [102] he gives a sign to support what he posited earlier about generation of dew and frost. And he says that a sign of the fact that dew and frost are caused by the fact that vapor is not lifted far above the earth is that frost does not appear on mountains, whereas it would seem that, on account of the cold there present, it should appear there even more. There are two reasons for this: First, because the vapor from which dew and frost are generated is raised from low, moist, places, from which many vapors are generated and lifted up: hence the heat which elevates them, bearing, as it were, a burden too much for its power, cannot raise them to a very great height; hence, while still near the lowest places, the heat leaves the vapors, and dew and frost fall. That is why frost cannot form on high mountains. The second cause is that, as previously stated, the upper air above the mountains flows along, as though carried by the course of the heaven; and therefore, by its flowing it dissolves such gatherings of vapor that cause dew and frost. Now, more motion is needed for scattering large amounts of vaporous matter than small amounts: but the matter of rain and snow coalesces in large amounts, whereas the matter of dew and frost is, absolutely speaking, small, although it is large in relation to the small amount of heat elevating it: hence neither rain nor dew nor frost fall on the highest mountains, because of the greater flow of air; but on mountains that are not so lofty, rain and snow, but no dew or frost, fall, because of the lesser flow of air.

107. Then [103] he shows under what circumstances dew in particular occurs. About this he does three things: first, he proposes a truth and says that dew forms in all places with south winds that are not strong enough to prevent vapors from gathering. It does not form with the blowing of the north wind except in the region of Pontus, which is very cold: there the opposite takes place, for dew forms there with northerly weather but not with southerly weather.

108. Secondly [104], he assigns the cause of what generally happens and says that the cause of this is akin to what has been said: namely, that dew forms in temperate times but not in "winter," i.e., in very cold times. And he shows the point of similarity: the south wind brings mildness, but the north wind winter and cold, for it is a cold wind; and therefore, because of the "winter," i.e., because of the coldness, the warmth is extinguished from exhalations, and, as a result, the vapors cannot be elevated for dew to be formed.

109. Thirdly [105], he assigns the cause of what happens in Pontus. The reason is that, because of the great cold there, the south wind is unable to produce sufficient mildness for vapors to be elevated: therefore no dew forms there during the time of the south wind. But the north wind, because of its coldness, collects the warm matter existing in damp places, "making a kind of anti-surrounding," i.e., by surrounding the warm matter with a certain contrariety — for when cold matter surrounds warm matter, if the former cannot completely quench the latter, it concentrates it. Thus, by the concentration of the hot, its effect is strengthened — and, as a result, more vapor is resolved.

This occurs not only in Pontus but is frequently observed in other places: wells evaporate more with a north wind than with a south wind, because of the heat trapped in them by the surrounding cold. However, in other places the coldness of the north wind quenches the vapor's heat before any can be concentrated in amounts large enough to generate dew; but when there are south winds, they do not impede the accumulation of vapors needed for generating dew. Even in Pontus there are times when, because of the north wind, the heat of the vapors is quenched and, therefore, do not rise; but sometimes, because of the greatness of the cold, much warmth is enclosed within the earth and a large amount of vaporous exhalation forms, in such a way that, for a brief time, it resists the air's coldness, but only long enough for an amount sufficient for the generation of dew to be accumulated.

He says therefore first [106], that although vapor freezes in this lower air near the earth, yet water does not coagulate here to form hail as it coagulates in the region of the clouds. For three bodies condensed by cold come from that region: namely, rain water, snow and hail. But in the case of two of these bodies, certain proportionate things take place in the lower region near the earth, and which are generated from the same causes, but differ from rain and snow according to more and less, depending, namely, on whether they are produced more quickly or more slowly, and on largeness and smallness [of amount].

For snow and frost are proportionately the same, and likewise rain and dew: they differ according to abundance and scarcity. For rain comes to be from the cooling of an abundance of vapor — the cause of this abundance being a large

and spacious region and a long time in which the vapor is being united and collected, and also a large place from which it is collected. For, since rains are generated on high, vapors collect there from many regions. Dew, on the other hand, has little vapor, because the time is short during which it is collected (for the consistency of that vapor is "ephemeral," i.e., of a single day), and the region is small in which it is collected, for it is collected close to the earth — and this becomes plain fro ggy the fact that the generating of dew is swift and its amount is small. And as it is with dew and rain, so with snow and frost: for when an entire cloud is frozen, snow comes to be; but when some small vapor near the earth freezes, frost comes to be. Therefore, both of them are a sign of cold weather or of a cold region — for, since some heat still abides in both the vapor and the cloud, they would not freeze, unless there were present a vast coldness overwhelming that heat: there being in the cloud still a large residue of the heat which made the watery moisture evaporate from the earth, and in the vapor still more. Thus, as rain and snow come to be in the upper region, so dew and frost in the lower. But although hail comes to be in the upper region, nothing below corresponds to it: the reason for this will be plain, when the cause of the generation of hail is explained.

111. Then [107] he proposes certain phenomena that occur with respect to hail and create a difficulty as to its generation;

He says therefore first [107], that with respect to the generation of hail we must consider the facts which are thought to be reasonable, and not false. And first he proposes that hail is, as it were, "crystal," i.e., water solidly frozen; he further proposes that water freezes especially in winter. But the contrary is seen to happen: for hailstorms occur mainly in spring and autumn; and after this, during the time of fruit, i.e., in summer and around the onset of autumn; but less often in winter, and, in that case, when the cold of winter has been less. Generally speaking, hail occurs in more temperate places; snow in colder places and times. From all this it would seem that hail, in which a larger amount of freezing is involved, ought rather to occur in places and times that are cold.

112. Then at [108] he presents a second difficulty, about which he does three things. First, he presents the difficulty and says that it appears inconsistent that water should freeze on high — for it cannot freeze before it is formed, nor after it is formed, can it remain aloft, since it falls immediately. Hence it does not appear that there can be time for it to freeze and generate hail.

113. Secondly, he gives an apparent solution of this difficulty [109]. For one could say that the water, separated into minimal parts, remains in the air as though mingled with it, and does not fall at once, but abides in the air. This is what happens when "psecades" [droplets] fall, about which we spoke earlier. And a like thing is true of earth in respect to water, which is to earth, as air is to water: for often gold or earth float on water because of the minuteness of their particles; but if those particles of earth or gold coalesced, they would fall to the bottom of the water. Hence as a result of the small particles that abide in the air congregating, large drops are formed and, in this way, the drops are brought down. In like manner, one could say that it is not impossible for water permeating the air to freeze and form hail.

114. Thirdly [110], he rejects this solution and says that what happens to occur in droplets does not occur in the case of hail. For bits of frozen water, if small, could not consolidate to form something large like hailstones in the way that the parts of water, as moist, coalesce: for hard objects, such as ice, do not unite the way more moist things do. Hence a quantity of water equal to the size of the hailstone would have had to be hanging above in the air without falling: this is evident, for it could not be the size it is after freezing, if it had not been that size before freezing — since from many small things cannot be formed many large continua. But that such an amount of water should remain above without falling seems impossible.

115. Then [111] he assigns the cause of the generation of hail.

About the first he does two things: first, he presents the opinions of others [111] and says that it seems to some that when a large quantity of heat pushed a cloud into the upper region, which is very cold because the rays reflected from the earth do not reach there, the water arriving there is frozen on account of the region's being cold. And therefore the reason why hail occurs during the summer and in warm regions is that vast heat greatly pushes clouds into the upper region far from earth.

116. Secondly [112] he attacks this position on three scores. First, we see that hail does not occur on lofty mountains — but it should, if hail is formed by vapor lifted into very high places, just as we see snow, which is generated on high, on lofty mountains.

117. He gives the second argument [113] and says that clouds are often seen moving with a great noise close to the earth so that some people hearing it fall down in terror, as though it augured a great prodigy. At other times, when such clouds are seen near the earth without any noise, a great hailstorm occurs, with hailstones of incredible size and non-round shape. Now, these phenomen