sluggish or the swiftest of motion, whether God causes all things to revolve round us or causes us to revolve. Now, for this it is essential that we have a record of all the appearances of comets in former times.
For, on account of their infrequency, their orbit cannot as yet be discovered or examined in detail, to see whether they observe periodic laws, and whether some fixed order causes their reappearance at the appointed day. Such a development of astronomy is recent, having been lately introduced into Greece.
III Democritus, the most acute of all the ancient philosophers, says he 1 suspects there are several stars whose orbits are erratic. But he has given neither their number nor their names, as the motions of the five planets were not in his time understood. Eudoxus was, in fact, the first to import from Egypt into Greece the knowledge of these motions, though he says nothing about comets. From this it becomes plain that, even among the Egyptians, the people that bestowed most care on observation of the sky, the portion of astronomy that relates to comets had not been worked out. Subsequently Conon, who was himself a 2 careful investigator, made a record of the sun’s eclipses that had been observed by the Egyptians; but he made no mention of comets, though he would certainly not have omitted anything definite on the subject that he had learned in Egypt. So much is certain; two authors, Epigenes and Apollonius of Myndus, the latter highly skilled in casting horoscopes, who say that they studied among the Chaldaeans, are at variance in their accounts. The latter asserts that comets are placed by the 3 Chaldaeans among the number of the wandering stars (_i.e._ planets), and that their orbits have been determined. Epigenes, on the contrary, asserts that the Chaldaeans have ascertained nothing regarding comets, which are thought by them to be fires produced by a kind of eddy of violently rotating air.
IV In the first place, if it like you, let us set down the views of the 1 last-mentioned author and refute them. He supposes that the planet Saturn has most influence in determining all motions of the heavenly bodies. When it presses upon the constellations next Mars, or crosses to the neighbourhood of the moon, or encounters the rays of the sun, being naturally cold and windy, it contracts and masses the atmosphere at more than one place. By and by, if Saturn absorb all the sun’s rays, there is thunder and lightning. If he has Mars in agreement, the 2 lightning is forked. Moreover, he continues, forked and sheet lightning contain different materials. Evaporation from water or other moisture produces only gleams that threaten but stop short of striking. The hotter and drier exhalation of the earth forges the bolts of forked lightning. Beam meteors and torches, which differ from one another 3 only in size, are produced in this same way. When any ball of air--what we call a whirlwind--encloses moist earthy matter, wherever it rushes it presents the appearance of an extended line of fire, which lasts just so long as the mass of air remains, which carries within it the supply of moist earthy matter.
V This account of Epigenes is a tissue of falsehoods. To begin with the 1 nearest one, the last, it is not true that torch and beam meteors are due to the violent action of a whirlwind. The whirlwind is formed in the neighbourhood of the earth, and there it runs its course. This is the reason why it tears up trees by the roots, and wherever it swoops down it lays bare the soil, carrying off in the meanwhile woods and roofs of houses; as a rule, it is lower than the clouds, and assuredly never higher. But, on the contrary, it is the more exalted part of heaven that displays beam meteors, and so they never intervene between us and the clouds. Besides, a whirlwind is borne along more swiftly than any cloud, and rotates as on a pivot. And in addition to this, it 2 ceases all of a sudden, bursting by its own force. “Beams,” on the contrary, do not run or fly across, like torches, but remain shining for some time in the same quarter of the sky. Charimander, too, in the book he wrote on comets, asserts that a great and unusual light in the sky of the size of a large beam was once seen by Anaxagoras, and continued to shine for a long period. Callisthenes puts it on record that a similar appearance of a trail of fire was observed before the sea swallowed up Buris and Helice. Aristotle says it was not a “beam,” 3 but a comet; the characteristic dispersion of the fire was not seen at first on account of its excessive brightness, but, in process of time, when the glare began to die down, it recovered the distinctive appearance of a comet. In this fiery phenomenon there were many points worthy of remark, none more so than this, that, immediately it shone in the sky, the sea came over Buris and Helice. Did Aristotle, then, one 4 may ask, believe that not merely that beam but all beams are comets?
Surely not, for there is this difference, that beams have their fire continuous, while in the other bodies it is dispersed. Beams have a regular flame, not interrupted or dull at any point, while in the end parts it is condensed, just like what Callisthenes describes the one to have been, to which I referred a moment ago.
VI There are, Epigenes goes on to say, two classes of comets. One kind 1 sheds its light on all sides without changing its position; the other extends a loose kind of fire in one direction, after the fashion of hair, and passes through among the stars; of the latter kind were the two seen in our own days. The former variety, with hair on all sides, that do not move, are usually low down, and arise from the same causes as beams and torches, that is, from a distempered thick atmosphere that carries in it many of the earth’s exhalations, both dry and moist. Air driven out through narrow apertures is capable of setting on fire 2 the atmosphere situated over it, which is full of elements suitable for feeding a fire; and it is able after that to drive it forward from the clear space, lest from any cause it should fall back and relax its force. After that, it can rise again on the next and following days and set fire to the same spot. As presumptive proof of this, we see winds return during several days at their set time. Rain, too, and storms in other forms recur according to appointment. His opinion may be briefly expressed by saying that he supposes comets to be formed 3 pretty much in the same way as fires excited by whirlwind. There is this one difference, that those whirlwinds are pressed down to earth from a higher region, while these others are raised from earth to the upper regions.
VII A great deal can be urged against this view. First of all, if wind 1 were responsible, a comet would never make its appearance without wind.
As a matter of fact, it appears when the air is perfectly still. In the next place, if it were due to wind, it would fall with the wind; and if it began through wind, would increase with increase of wind, and would be the brighter the more furious the wind was. This point, too, has to be added to the foregoing: while the wind impels many parts of the atmosphere, a comet appears in one spot. The wind does not mount up high, but comets are seen higher up than the winds are permitted to go. Epigenes afterwards goes on to speak of the comets that, he 2 says, have a more definite resemblance to stars, traversing an orbit and passing through the zodiacal signs. He attributes their origin to the same causes as produce those that he called lower comets, the only difference being that the earth’s exhalations in this case contain many dry elements, and therefore seek the higher region, and are driven by the north wind toward the more exalted portions of the heavens. But, surely, if the north wind urged them, they would always be borne toward the south, whither this wind urges its course. And yet, as a fact, they 3 have had different movements, some to east, others to west, all in a curved path, a direction which the wind could not impart. Besides, if the impulse which produced the comet carried up on high those north winds from the earth, comets would not arise when other winds blew; yet they do arise.
VIII Let us now refute this other explanation of Epigenes, for he employs 1 two. He believes that when all the moist and dry exhalations of the earth unite, the mere discord of the different bodies turns the air into whirlwind. Then the force of that wind as it revolves sets fire by its rapid motion to all that it embraces in itself, and raises it on high. The gleam of the fire that is thus extracted remains as long as there is sufficient nutriment; when the fuel fails, the fire subsides too. Now, one who talks thus pays no attention to the nature of the 2 course of whirlwinds as compared with that of comets. The career of the former is swift and violent, more rapid than the winds themselves.
But a comet’s movement is so gradual as to render imperceptible the space traversed during a day and a night. Besides, whirlwinds have an erratic, disorderly, and, to use a word of Sallust’s, eddying, motion. Comets have a regular course, which observes the appointed track. Surely none of us will believe that either the moon or the five planets are carried by the wind or spun round by the whirlwind.
I trow not. And why? Just because they have not an irregular and 3 unrestrained motion. Let us apply the principle to comets. They do not move in confusion or irregularity so as to justify the belief that they are impelled by unruly and fickle forces. Besides, even if those eddies could enclose moist earthy elements, and had power to raise them from the depths to the heights, still they could not carry them up higher than the moon. All their force is spent when they reach the region of clouds. But as for the comets, we see them sailing through the upper regions, mingling with the very stars. It is, therefore, improbable that a whirlwind could persist over such a long distance, for the greater it is, the more rapidly is it spent.
IX Let Epigenes, therefore, make his choice of the two alternatives: 1 if the force is small, it cannot reach so high; if it is great and violent, it will the more quickly break up. But further, according to the opinion of people like Epigenes, these lower comets do not mount higher because they have too much earthiness in them. Their weight keeps them in the neighbourhood of earth. And yet these other comets, which are higher and last longer, must have a more abundant material.
For they could not last so long were their supplies not replenished from a larger stock. I said a moment ago that the whirlwind’s eddy 2 could not long endure, nor could it mount higher than the moon, or as far as the place of stars. Of course, the whirlwind is caused by the mutual struggle of several winds, and the contest cannot be kept up for any long time. When the wandering uncertain air assumes a rotatory form, in the last instance the force of all the winds yields to the single strongest one. No hurricane lasts long. The more strength 3 squalls have, the shorter their duration. When winds reach their maximum, they quickly abate all their violence. By that headlong speed they must needs hasten to their own destruction. So no one has ever seen a whirlwind last a whole day, or even an hour. Its velocity is astonishing, its brevity no less astonishing. Moreover, on the earth and near it, its rotation is swifter and more violent; the higher it 4 is, the less condensed and compact is it, and that is the reason of its more rapid dissipation. Add the fact, too, that even if it reached the highest region where the stars’ path lies, it would most certainly be broken up by the motion which causes the universe to revolve. For what can compare in rapidity with the revolution of the world? Thereby the strength of all the winds combined in one would be shattered, aye, and the strong solid chain that binds the earth, not to say a wisp of whirling air.
X Again, a fire carried along by a whirlwind cannot remain on high 1 unless the whirlwind also remain. But then what is so inconceivable as any prolonged duration in a whirlwind? Above all, the whirlwind motion is neutralised by the opposite motion of the heavens. That region on high to which it is alleged to mount has an eddying motion of its own, which carries onward the sky, And drags the lofty stars, and turns them in rapid whirl.
And even though one grant some duration to whirlwinds, which is quite contrary to the fact, yet what is to be said of the comets that have continued in sight for six months? Then, as hinted above, there 2 must be two motions in the same spot--one that constant motion of the heaven, accomplishing its task without intermission, the other a strange new motion conveyed by the whirlwind. The one must inevitably obstruct the other. And yet that motion we see of the moon in her orbit, and of the other heavenly bodies that pass above the moon, is irrevocable. It nowhere falters or stops, nor does it convey to us the slightest suggestion of an obstacle being ever placed in its way.
It is utterly beyond belief that a whirlwind, the most violent and 3 unruly species of storm, should reach the very centre of the ranks of the stars, and should find a sphere for its boisterous activity in that ordered peace of heaven. Supposing that the revolution of a whirlwind kindles fire, which is shot up to the heights, furnishing apparent ground for the belief that what we see is a trail of fire; yet surely the shape of the fire ought to be something like that which produces it. Now a whirlwind is round in appearance; it remains in the same 4 track, and revolves after the fashion of a rotating pillar. The fire, therefore, that is enclosed ought to resemble it in shape. But in reality it is a trail of scattered fire, and resembles anything rather than fire gathered into a ball.
XI Let us now say good-bye to Epigenes, and proceed to examine the 1 opinions of other writers. But before beginning to set them forth, I must first, by way of preface, remark that comets are not observed only in one part of the sky, nor merely in the zodiac, but in the east as well as in the west, more frequently, however, toward the north. Nor is 2 their shape uniform. The Greeks, indeed, distinguished three classes of them: those from which the flame hangs down, after the fashion of a beard; those that shoot out what looks like hair round them on all sides; and those which have a scattered kind of fire, which, however, stretches toward an apex.[92] But all the classes have a common characteristic, and are rightly called comets (_i.e._ long-haired). As the different shapes present themselves only at long intervals, it is difficult to compare them with one another. Even at the time of their appearance spectators are not agreed as to their shape. According 3 as one’s eyesight is keener or duller, one asserts that the comet is brighter or redder, and that its hair is compressed toward the interior of the star, or spread out toward its sides. But whether or not there are any differences in comets, they must all be produced by the same method. The one fact about which there ought to be agreement is, that 4 a star of strange unwonted appearance is beheld which drags along with it scattered fire. Some of the ancients are convinced of the truth of this explanation: When one of the planets has come into conjunction with another, the light of the two blends in one, producing the appearance of a more elongated star. This happens not merely when star touches star, but even when one approaches another. The space between the two is in that case lit up by both, and seems aflame, producing the trail of fire.
XII Our first answer to this theory is that the number of moving stars 1 (planets) is fixed. It is quite usual for them and comets to appear at the same time; whence it is manifest that the comet is not due to the conjunction of planets, but is a distinctive independent star.
Besides, it is a matter of frequent occurrence for a star to come under the orbit of a more elevated star. Saturn, for example, is sometimes above Jupiter; Mars looks down in a straight line on Venus or Mercury.
But yet no comet is formed from this movement whereby the one planet 2 approaches the other. Were it otherwise, there would be a comet every year, for every year there are planets in the same constellation.
Again, if the approach of star to star produced a comet, the latter would cease to be in a moment. The transit of stars takes place with the utmost rapidity, thence all eclipse of heavenly bodies is of brief duration; by the same motion they are as swiftly separated as they were brought together. The sun and the moon, as we see, part company 3 within a brief space after the eclipse has begun. How much swifter must be the separation of stars, which are so much smaller? Yet comets last for six months at a time, which would not happen if they sprang from the union of two stars. The stars cannot stick to one another for any long time, and the law of their swift motion must ever drive them asunder. Besides, those stars appear to us to be close to one 4 another, but in reality are separated by immense distances. How, then, could the one star transmit fire to the other so that the two should seem in union, when they are thus parted by an immense tract? The light of the two stars, it is replied, mixes, furnishing the appearance of one. I suppose this means that the phenomenon is much the same as when a cloud takes a ruddy colouring from the rays of the sun striking on it, or as when there is the golden glow of evening or morning, or as when the bow is painted in its varied hues, but only in sunshine.
Well, my first criticism is that all the instances mentioned are the 5 result of great force. It is the sun that lights them up. The stars do not possess anything like the same power. My second remark is that none of the phenomena arises except below the moon in the vicinity of the earth. The upper regions are pure and spotless, always retaining their own colour. I remark further, that if anything of the kind did occur, it would not last but would speedily disappear, as halos which surround the sun or moon fade in a very brief space of time. Even the rainbow 6 does not long remain. If there was anything of the kind supposed, to unite the space between the two stars, it would disappear with equal rapidity. In any case it would not remain as long as comets are in the habit of doing. The planets have their orbits within the zodiac, they lie near this circle; but comets are seen in all parts of the sky.
Their time of appearance is no more certain than the limits of the space which they may not exceed.
XIII In reply to arguments like mine it is urged by Artemidorus that the 1 five planets are not the only stars with erratic courses, but merely the only ones of the class that have been observed. But innumerable others revolve in secret, unknown to us either by reason of the faintness of their light, or the situation of their orbit being such that they become visible only when they reach its extremities. It is thus, he says, that certain new stars enter our field of vision, 2 mingling their light with the fixed stars, but displaying a brightness greater than is usual in stars. This is the least serious of his lies: his account of the universe is from end to end a shameless tissue of lies. For instance, if we are to believe him, the upper regions of heaven are perfectly solid--a lofty thick vault, as hard as the roof of a house, formed by the accumulation of masses of atoms. The surface immediately above it is of fire so compact that it cannot be broken up or altered. Nevertheless, it has certain ventilators, and, as 3 it were, windows through which portions of the fire stream from the outer part of the universe, but not so large as to cause commotion in the inner; and again the fires pass from the world back into the outer spaces. These extraordinary appearances, therefore, Artemidorus supposes, have streamed in from that mass of matter which lies outside the world. To set about disproving such a theory is nothing short of beating the air for the sake of exercising the muscles!
XIV Still, I will descend to the task. Let the man who has placed such a 1 solid roof on the world tell me what reason there is for believing his statement that the heavens have such a thickness. What was it that took all these solid bodies up there and kept them there? Then, a firmament of such thickness must necessarily be of immense weight too. How is it that heavy bodies remain aloft? How is it that the huge mass does not come down and smash itself by its own weight? It is, I imagine, a 2 physical impossibility that such a vast weight as Artemidorus has brought to the support of the heavens should hang suspended, or be supported by a slight foundation. Nor can it be alleged that there are stays[93] of some kind outside by which it is prevented from falling.
Nor again can there be any support in the centre[94] to receive and prop up the threatening mass. And again, no one will venture to assert that the universe is being constantly carried down through the immensities of space, falling all the time, though it is not evident that it falls, because its headlong course is to all eternity, having no final obstacle with which to collide. This is indeed a statement people have made about the earth, when they could discover no 3 explanation for a mass standing poised in air. It is borne down, say they, for ever; but it is not evident that it falls because the space into which it falls is endless.
[93] The word is usually applied to a flexible fastening, hawser, cable, or the like.
[94] Or, between the earth and it.
Well, what argument[95] then justifies the assertion that it is not merely the five planets that move, but that there are many such in many quarters of the universe? Or if there is no probable proof of this, one may rejoin: What is there to prevent one from saying either that all the stars move or that none of them does? Besides, your argument 4 is in no way helped by that crowd of stars which you assume to be everywhere roaming about! For the more there are of them, the oftener will they meet with others; whereas comets are rare, and for that reason marvellous. And will not every age give evidence against you by noting and recording for the use of posterity the emergence of such stars?
[95] The argument is resumed from the beginning of XIII. after the digression about the “firmament.”
XV After the death of Demetrius, king of Syria, whose kingdom was 1 divided by his sons Demetrius and Antiochus, a little before the Achaean War, a comet blazed forth not inferior to the sun in size.
Its orb was at first fiery red, and emitted a bright light sufficient to dispel the darkness of night. By and by its size was gradually reduced and its brightness waned. Finally it went completely out. How many stars, suppose you, would require to combine to make up such a huge mass? You might collect in one a thousand of them without ever 2 matching the size of the sun. In the reign of Attalus a comet appeared, moderately small in size to begin with. By and by it mounted up and spread out and moved as far as the equator, equalling in the extent of its immense length the whole quarter of the sky which we call the Milky Way. How many planets must have combined to occupy with an unbroken line of fire such a long tract of the sky?
XVI I have refuted the argument; I must now discredit its authors. It 1 requires no great effort to strip Ephorus of his authority; he is a mere chronicler. Some of his class seek to recommend their narrative by incredible stories, and by their marvels try to interest the reader, who would probably soon find some other occupation if he were called on to wade through their tedious narrative of ordinary events. Some, again, are too credulous, some too careless, some are deluded, some delighted, by falsehood. The former do not shun it, the latter go in quest of it. The whole clan of them have this in common; they fancy 2 their work cannot merit approval, and become popular unless they freely interlard it with lies. Ephorus is not a person of any scrupulous honour; he is often duped, often he tries to dupe. For example, he asserts that the great comet which, by its rising, sank Helice and Buris, which was carefully watched by the eyes of the whole world since it drew issues of great moment in its train, split up into two stars; but nobody besides him has recorded it. Who, I wonder, could observe the moment at which the comet broke up and was resolved into two 3 parts? And if there is any one who saw it split up into two, how is it that no one saw it first formed out of the two? And why did Ephorus not add the names of the two stars into which it was broken up, since they must have been some of the five planets?
XVII Apollonius of Myndus differs in his view from Epigenes. He asserts 1 that a comet is not one star made up of many planets, but that many comets are planetary. A comet, he goes on, is not an illusion nor a trail of fire produced on the borders of two stars, but is a distinctive heavenly body, just as the sun or the moon is. Its shape is not limited to the round, but is somewhat extended and produced lengthwise. On the other hand its orbit is not visible. It cuts 2 (=intersects) the upper part of the universe, but only emerges when at length it reaches the lowest portion of its course. There is no reason to suppose that the same comet reappears; for instance that the one seen in the reign of Claudius was the same as the one we saw in the reign of Augustus; or that the recent one which appeared during the reign of Nero Caesar--which has redeemed comets from their bad character--was similar to the one which burst out after the death of the late Emperor Julius Caesar, about sunset on the day of the games to Venus Genetrix. Comets are as varied as they are numerous. They are 3 unequal in size, unlike in colour. Some are ruddy without any light; others are bright with a pure clear light; others are flame-coloured, but the flame is not a pure thin flame, but is enveloped in a mass of smoky fire. Some are blood-stained and threatening, bringing prognostication of bloodshed to follow in their train. They wax and wane like other planets. They are brighter when they come down toward us, and show larger from a nearer point, smaller when they depart from us, and dimmer when they retire to a greater distance.
XVIII The reply is ready to this last statement, that the same thing does 1 _not_ happen in comets as in the other stars. Some comets attain their maximum on the very first day of their appearance. But, according to the argument, they ought to increase the nearer they approach. As it is, their first aspect remains until they begin to fade. Besides, what has been said in reply to former authorities applies here too: If the comet had an erratic orbit, and were a true planet, it would move within the limits of the zodiac, within which all the planets confine their orbits. Again, a star is never seen through another star. 2 Our sight cannot pierce through the centre of a planet so as to view through it what lies beyond. But through a comet the further regions are discerned as through a cloud. Whence it is evident that it is no planet but an insubstantial, irregular fire.
XIX The following is the opinion of our Stoic sage Zeno. He is convinced 1 that the stars act in concert, and unite their rays with one another--a partnership in light which creates the image of a more elongated star.
Therefore some persons suppose that comets have no real existence, and that it is only the appearance of them that is reproduced through the reflection of neighbouring stars or the union of stars that stick 2 together. Some, again, say that comets are true stars, but with orbits of their own, and that after certain periods they come out into the view of mankind. Some allow their existence but refuse them the title of stars, because they glide out of sight without long duration, and within a brief space are scattered to the winds.
XX Most of our Stoic brethren entertain another view, which they do not 1 regard as inconsistent with fact. Let me explain it. We observe many species of fire engendered on high, now the heavens ablaze, now Long glistening trains of flame behind, now huge torches of fire being hurried along. The lightning itself, whose velocity is so marvellous that it at once blinds, and at the same instant restores, the sight, is fire arising from the friction of air that suffers more violent internal pressure than usual. That is why it does not remain long, but glides off once it issues from 2 the cloud, forthwith perishing. But other fiery appearances remain for a considerable time, and do not break up until all the fuel on which they fed has been used up. Here belong the strange sights recorded by Posidonius--pillars and shields all ablaze, and other flames of marvellous strangeness. They would attract no attention if they ran their course after customary laws; but now the sight of them sends all men agape. They bring down sudden fire from the heights of heaven, 3 sometimes producing a flash which is gone in a moment, sometimes compressing the air, which is forced into a glow; it is a miracle all the same. Yes, and is not sometimes a gulf opened in the ether, which seems to retire on all sides, with a great glare of light in the hollow centre? You are ready to cry out. What is this?...I see the very centre of heaven open, And the stars wandering in the sky...These stars sometimes do not wait for night to show their light, but burst out in the full light of day. The reason, however, for the stars showing at a time not their own is different from that alleged; it 4 is well known that they are there all the time, though hidden. Many comets, too, we cannot see because they are obscured by the sun’s rays.
Posidonius, in fact, tells us that during an eclipse of the sun a comet once appeared which the sun’s proximity had hitherto concealed. Often, when the sun has just set, straggling fires[96] are seen close to him.
No doubt the nucleus of the comet is bathed in sunlight, and therefore cannot be discerned; but the tail escapes the effect of the sun’s rays.
[96] _I.e._ the tail of a comet.
XXI Our Stoic friends, therefore, are satisfied that, like trumpet meteors 1 and beams, and other portents of the sky, comets are formed by dense air. They appear in greatest number toward the north, because there is most of the sluggish air there. Why, then, you naturally ask, does the comet not remain stationary, but advance in the sky from day to day? Let me explain. The comet, according to this account, pursues its fuel just as fires do. Although its tendency is to rise to the upper regions, still, if material fail it, it retrogrades and sinks. In the air, too, it does not pursue a direct path to right or left. It has no particular route assigned to it; wherever the supply 2 of its fuel leads it, thither it crawls; it does not advance in its orbit as a star, but feeds as a fire. Why, then, does it appear for a long period, and why is it not quickly extinguished? For the recent one which we saw during this joyous reign of Nero displayed itself to view for six months, revolving in the opposite direction to the former one in Claudius’ time. That one rising from the north up toward the zenith made for the east, always growing dimmer. This one began in the same quarter, but making toward the west, turned finally toward the south, where it withdrew from view. No doubt the former found moister elements, more suitable for its fire, and pursued them; the latter 3 in turn chose a richer and more substantial district. So they descend toward the direction in which they are invited by their material, and not by a definite path, which in the two we have seen was different, since the one moved off toward the right and the other toward the left.
Now all stars[97] have their orbit in one direction, namely, contrary to the motion of the universe. The latter moves from east to west, the stars go from west to east. For this reason they have a double motion,--one, their own proper motion; the other, which carries them round along with the heavens.
[97] Planets may be specially referred to; the Latin word is the generic one, _stella_.
XXII I do not agree with my school here, for I cannot think a comet is a 1 sudden fire, but I rank it among Nature’s permanent creations. First of all, everything that the atmosphere creates is short-lived; such things arise in an element that is fugitive and changeable. How can anything continue the same for long in the air, which itself never remains the same? It is always in a state of flux, and its quiet is short-lived. It changes within a brief moment to another condition from that in which it had been. It is now rainy, now clear, now alternates from one to 2 the other. The clouds, so intimately connected with it, into which it collects and from which it is released again, now gather, now disperse, but never remain at rest. Fire cannot possibly abide securely in a volatile body, nor can it keep its place so persistently as does a fire that Nature has fixed never to be dislodged. Further, if the fire stuck close to its fuel, it would always sink. For the air is the thicker, 3 the nearer it is to the earth. But a comet is never depressed to the lowest strata of the atmosphere, nor does it ever approach the ground.
Besides, fire either goes in the direction its nature prompts, that is, upwards, or else in the direction in which it is drawn by the material on which it has fastened, and on which it feeds.
XXIII In none of the ordinary fires in the sky is the route curved; it 1 is distinctive of a star (planet) that it describes a curve in its orbit. Whether other comets had this circular orbit I cannot say.
The two in our own age at any rate had. Again, everything kindled by a temporary cause quickly gives out. Thus torches gleam only while they flit across the sky; thus lightning has strength for just one stroke; thus so-called shooting and falling stars fly past, cutting through the air. No fires have any considerable duration unless 2 their strength is inherent. I mean the divine fires which the universe maintains eternally, because they are its parts and works. These, I say, are always active; they have an orbit the even tenor of which they