So much for the hypothesis, that both stars and circles are in motion. Let us now assume that one is at rest, and the other in motion; and first, let the circles be at rest, and the stars in motion. This again will lead to absurdities; for we shall still be unable to explain how it happens that the outermost stars are moved most quickly, and that their velocities are proportioned to the magnitudes of the circles.
Since then we cannot assume either that both are moved, or that the star alone is moved, we must adopt the third supposition, that the circles are moved, and that the stars, being themselves at rest, are fastened in the circles and carried round along with them. This is the only hypothesis which entails no unreasonable consequences. For it is reasonable that, of circles fastened round the same centre, the greater velocity should belong to the greatest. For, as in all the varieties of body the heavier fragment is carried with greater velocity than the lighter in its appropriate motion, so it happens with the encyclical body. When two straight lines are drawn from the centre, the segment of the greater circle intercepted between them will be greater than the segment of the smaller; and it is consistent with reason that the greater circle should be carried round in equal time. This is one reason why the Kosmos is not split intoseparate parts; another reason is, because the universe has been shown to be continuous (s. 4, 5).
Now we all agree that the stars are of spherical figure: and spherical bodies have two motions of their own — rolling and rotatory (κύλισις καὶ δίνησις). If they were moved of themselves, they would be moved in one or other of these two ways; but we see that they are so in neither. They do not rotate; for, if they did, they would remain always in the same place, which contradicts universal observation and belief. Besides, it is reasonable to suppose that all the stars move in the same manner, but the Sun is the only one that is seen so to move, when he rises or sets; and he too, not by any movement of his own, but through the distance of our vision, which when stretched to a great distance, rotates from weakness (s. 6). This is perhaps the reason why the stars fastened (in the outer sphere) twinkle, while the planets do not twinkle; for the planets are near to us, so that our vision reaches them while yet strong; whereas in regard to the unmoved stars it is made to quiver in consequence of the great distance from being stretched out too far, and its quivering causes the appearance of motion in the star. For there is no difference between moving the vision and moving the object seen (οὐθὲν γὰρ διαφέρει κινεῖν τὴν ὄψιν ἢ τὸ ὁρώμενον — s. 6).
Again, neither do the stars roll nor revolve forward. For that which rolls forward must necessarily turn round; but the same side of the moon — what is called the face of the moon — is always clearly visible to us (s. 7).
Since it is reasonable to believe, therefore, that, if the stars were moved in themselves, they would be moved in their own special variety of motion (i.e., rolling or rotatory), and since it has been shown that they are not moved in either of these two ways, we see plainly that they cannot be moved in themselves (but are carried round in the revolution of the Aplanês).
Besides, if they were moved inthemselves, it is unreasonable that Nature should have assigned to them no organ suitable for motion, since Nature does nothing by haphazard; and that she should have been considerate in providing for animals, while she overlooked objects so honourable as the stars. The truth rather is, that she has withheld from them, as it were by express purpose, all aids, through which it was possible for them to advance forward in themselves, and has placed them at the greatest possible distance from objects furnished with organs for motion (s. 8).
Hence it would seem to be the reasonable doctrine — That the entire Heaven is spherical, and that each of the stars (fastened in it) is also spherical. For the sphere is the most convenient of all figures for motion in the same place, so that the Heaven being spherical would be moved most rapidly and would best maintain its own place. But for forward motion the sphere is of all figures the most inconvenient; for it least resembles self-moving bodies; it has no outlying appendage or projecting end, as rectilinear figures have, and stands farthest removed from the figures of marching bodies.
Since therefore it is the function of (δεῖ) the Heaven to be moved by a motion in the same place (κινεῖσθαι τὴν ἐν αὑτῷ κίνησιν), and that of the stars not to make any advance by themselves (τὰ ἄλλα δ’ ἄστρα μὴ προϊέναι δι’ αὑτῶν), it is with good reason that both of them are spherical. For thus will the Heaven best be moved, and the stars will best be at rest.
CH. 9. — From what I have said, it is plain that those who affirm that the revolving celestial bodies emit in their revolutions sounds harmonious to each other, speak cleverly and ingeniously, but not consistently with the truth. There must necessarily be sound (they say) from the revolution of such vast bodies. Since bodies near to us make sound in motion, the sun, moon, and stars, being so much larger and moving with so much greater velocity, must make an immense sound; and, since their distances and velocities are assumed to be in harmonic proportion, the sounds emitted in their revolution must also be in harmony. To the question put to them — Why do we not hear this immense sound? they reply, that we have been hearing it constantly from the moment of our birth; that we have no experience of an opposite state, or state of silence, with which to contrast it, and that sound and silence are discriminated only by relation to each other (ὥστε μὴ διάδηλον εἶναι πρὸς τὴν ἐναντίαν σιγήν· πρὸς ἄλληλα γὰρ φωνῆς καὶ σιγῆς εἶναι τὴν διάγνωσιν); that men thus cease to be affected by it, just as blacksmiths from constant habit cease to be affected by the noise of their own work (s. 1).
The reasoning of these philosophers (the Pythagoreans), as I have just said, is graceful and poetical, yet nevertheless inadmissible. For they ought to explain, upon their hypothesis, not merely why we hear nothing, but why we experience no uncomfortable impressions apart from hearing. For prodigious sounds pierce through and destroy the continuity even of inanimate bodies; thus thunder splitsup stones and other bodies of the greatest strength. The impression produced here by the sound of the celestial bodies must be violent beyond all endurance. But there is good reason why we neither hear nor suffer any thing from them; viz., that they make no sound. The cause thereof is one which attests the truth of my doctrine laid down above — That the stars are not moved of themselves, but carried round by and in the circle to which they are fastened. Bodies thus carried round, make no sound or shock: it is only bodies carried round of themselves that make sound and shock. Bodies which are fastened in, or form parts of, a revolving body, cannot possibly sound, any more than the parts of a ship moving, nor indeed could the whole ship sound, if carried along in a running river. Yet the Pythagoreans might urge just the same reasons to prove that bodies so large as the mast, the stern, and the entire ship, could not be moved without noise. Whatever is carried round, indeed, in a medium not itself carried round, really makes sound; but it cannot do so, if the medium itself be carried round continuously. We must therefore in this case maintain that, if the vast bodies of the stars were carried round in a medium either of air or of fire (whose motion is rectilinear), as all men say that they are, they must necessarily make a prodigious sound, which would reach here to us and would wear us out (διακναίειν). Since nothing of this nature occurs, we may be sure that the stars are not carried round in a current of their own, either animated or violent. It is as if Nature had foreseen the consequence, that, unless the celestial motions were carried on in the manner in which they are carried on, nothing of what now takes place near us (τῶν περὶ τὸν δεῦρο τόπον), could have been as it is now. I have thus shown that the stars are spherical, and that they are not moved by a motion of their own (ss. 2-5).
CH. 10. — Respecting the arrangement of the stars — how each of them is placed, some anterior others posterior, and what are their distances from each other — the books on astronomy must be consulted and will explain. It consists with the principles there laid down, that the motions of the stars (planets) should be proportional to their distances, some quicker, others slower. For, since the farthest circle of the Heaven has a revolution both simple and of extreme velocity, while the revolutions of the other stars (planets) are many in number and slower, each of them being carried round in its own circle in the direction contrary to that of the first or farthest circle of the Heaven, the reasonable consequence is, that that planet which is nearest to the first and simple revolving circle takes the longest time to complete its own (counter-revolving) circle, while that which is most distant from the same circle takes the shortest time, and the remaining planets take more or less time in proportion as they are nearer or farther. For the planet nearest to the first revolving circle has its own counterrevolution most completely conquered or overpowered thereby; the planet farthest from the same, has its own counterrevolution least conquered thereby; and the intermediate planets more or less in inverse proportion to their distances from the same, as mathematicians demonstrate.
CH. 11. — We may most reasonably assume the figure of the stars to be spherical. For, since we have shown that it is not their nature to have any motion of their own, and since Nature does nothing either irrational or in vain, it is plain that she has assigned to the immovables that figure which is least fit for motion; which figure is the sphere, as having no organ for motion. Besides, what is true of one is true of all (ἔτι δ’ ὁμοίως μὲν ἅπαντα καὶ ἕν): now the Moon may be shown to be spherical, first, by the visible manifestations which she affords in her waxings and wanings, next, from astronomical observations of the eclipses of the Sun. Since therefore one among the stars is shown to be spherical, we may presume that the rest will be so likewise.
CH. 12. — I proceed to two other difficulties, which are well calculated to perplex every one. We must try to state what looks most like truth, considering such forwardness not to be of the nature of audacity, but rather to deserve respect, when any one, stimulated by the thirst for philosophy, contents himself with small helps and faint approximations to truth, having to deal with the gravest difficulties.
1. Why is it, that the circles farthest from the outermost circle (or Aplanês) are not always moved by a greater number of motions than those nearer to it? Why are some of the intermediate circles (neither farthest nor nearest) moved by a greater number of motions than any of the others? For it would seem reasonable, when the First Body is moved by one single rotatory current, that the one nearest to it should be moved by two, the next nearest by three, and so on in regular sequence to those which are more distant. But we find that the reverse occurs in fact: Sun and Moon have fewer movements than some of the planets, which are nevertheless fartherfrom the centre, and nearer to the First Body. In regard to some of the planets, we know this by visual evidence; for we have seen the Moon when at half-moon passing under Mars, who was occulted by the dark part of her body, and emerged on the bright side of it. The like is attested respecting the other planets, by the Egyptians and Babylonians, the most ancient of all observers.
2. Why is it, that in the First Revolution (in the revolution of the First Heaven or First Body) there is included so vast a multitude of stars as to seem innumerable; while in each of the others there is one alone and apart, never two or more fastened in the same current?
Here are two grave difficulties, which it is well to investigate and try to understand, though our means of information are very scanty, and though we stand at so great a distance from the facts. Still, as far as we can make out from such data, these difficulties would not seem to involve any philosophical impossibility or incongruity. Now we are in the habit of considering these celestial bodies as bodies only; and as monads which have indeed regular arrangement, but are totally destitute of soul or vital principle. (When Aristotle here sayswe, he must mean the philosophers whose point of view he is discussing: for the general public certainly did not regard the Sun, Moon, and stars as ἄψυχα πάμπαν, but, on the contrary, considered this as blameable heresy, and looked upon them as Gods.)We ought, however, to conceive them as partaking of life and action (δεῖ δ’ ὡς μετεχόντων ὑπολαμβάνειν πράξεως καὶ ζωῆς); and in this point of view the actual state of the case will appear nowise unreasonable (s. 2). For we should naturally expect that to that which is in the best possible condition, such well-being will belong without any agency at all; to that which is next best, through agency single and slight; to such as are farther removed in excellence of condition, through action more multiplied and diversified. Just so in regard to the human body: the best constituted body maintains its good condition without any training at all; there are others which will do the same at the cost of nothing more than a little walking; there are inferior bodies which require, for the same result, wrestling, running, and other motions; while there are even others which cannot by any amount of labour attain a good condition, but are obliged to be satisfied with something short of it (s. 3). Moreover it is difficult to succeed in many things, or to succeed often: you may throw one or two sixes with the dice, but you cannot throw ten thousand; and, farther, when the conditions of the problem become complicated — when one thing is to be done for the sake of another, that other for a third result, and that third for a fourth, &c. — success, which may be tolerably easy when the steps are only few, the more they are multiplied, becomes harder and harder.
Hence we must consider the agency of the stars as analogous to that of plants and animals. For here the agency of man is most multifarious, since he is capable of attaining many varieties of good, and accordingly busies himself about many things and about one thing for the sake of others. The agency of other animals on the other hand is more restricted; that of plants yet more so, being of slight force and only of one special character (s. 4). But that which exists in the best possible condition stands in no need of acting or agency; for it already possesses that for the sake of which action is undertaken. Now action always includes two elements — that for the sake of which and what is for the sake thereof — the end and the means: there is either some one end, which the agent may attain, as in the case of man; or there are many different matters all of which may be used as means towards the best possible condition. Thus one agent possesses and partakes of the best possible condition; another comes near to it with little trouble; a third, with much trouble; a fourth does not even aspire to the end, but is competent only to arrive near to the last of the means. For example, let health be the end: one man is always in health; a second becomes so, by being starved down; a third by that, combined with running exercise; a fourth is obliged to take some additional exercise, in order to qualify himself for running, so that his motions are multiplied; a fifth is incapable of arriving at health, but arrives only at the running and the being thinned down, one of which in this case serves as end. For it would be best for all, if they could attain the supreme end — health; but, if that be impossible, then the next best thing is to get as near to the best as possible (ss. 5-7).
For this reason the Earth is not moved at all, and the matters near the Earth are moved with few motions; since they do not arrive at the extreme best, but only as near as their ability permits to obtain or hit the supremely divine principle; while the First Heaven, on the contrary, obtains or hits it at once, through one single motion; and the bodies intermediate between the First Heaven and those which are last (or nearest to theEarth), obtain it or arrive at it also, but only through a greater number of motions.
There is the other difficulty also to be considered — that vast multitude of stars are put all together in the one single First Current or Revolution, but each of the other stars (planets) has its own motions singly and apart. The principal reason of this we may fairly suppose to be that it follows as a natural consequence from the vast superiority of the first, in each variety of life and in each beginning, over all posterior to the first. Here the First Current or Revolution, being one and by itself, moves many of the divine bodies, while the others (secondary or countercurrents), numerous as they are, move each only one; for each one of these wandering bodies or planets is carried by many different currents. Thus Nature establishes equalization and a sort of symmetry, by assigning, in the one case, many bodies to one current, and in the other, many currents to one body (ss. 8-10). Beside this principal reason, there is also another. The other currents have each one body only, because motion is given to many bodies by all of them prior to the last which bears the one star. For the last sphere is carried round fastened into many spheres, and each sphere is a body (ss. 11, 12. I do not clearly understand the lines that follow:— ἐκείνης ἂν οὖν κοινὸν εἴη τὸ ἔργον· αὕτη μὲν γὰρ ἑκάστῃ ἡ ἴδιος φύσει φορά· αὕτη δὲ οἷον προσκεῖται. παντὸς δὲ πεπερασμένου σώματος πρὸς πεπερασμένον ἡ δύναμίς ἐστιν.).1
1[See Prantl’s note on this difficult passage in his German translation of the De Cœlo, p. 309 (Leipzig, 1857).]
1[See Prantl’s note on this difficult passage in his German translation of the De Cœlo, p. 309 (Leipzig, 1857).]
CH. 13. — Having thus explained, respecting the Stars and Planets which are carried round in circular motion, what is their essence, figure, current, and order of position, we now proceed to speak of the Earth: What is its position? Whether is it at rest or in motion? What is its figure?
Philosophers differ respecting the position of the Earth. Most of those who conceive the entire Kosmos as finite, declare the Earth to be in its centre. But the Italian philosophers, called Pythagoreans, are of an opposite opinion; affirming that Fire is in the centre, and that the Earth, being one of the stars revolving round the centre, makes night and day. They assume moreover another Earth opposite to this (ἐναντίαν ἄλλην ταύτῃ) — which other they callAntichthon. Herein they do not adjust their theories and look out for causes adapted to the phenomena; but, on the contrary, they distort the phenomena so as to suit their own doctrines and reasonings, and try to constitute themselves auxiliary governors of the Kosmos (πειρώμενοι συγκοσμεῖν — s. 1). And, if we are to look for assurance not to the phenomena but to our own reasonings, many others might agree with them, that it is not proper (μὴ δεῖν) to assign to the Earth the central place. They think that the most honourable place belongs to the most honourable body, and that Fire is more honourable than Earth; that the two extremes, centre and circumference, are more honourable than the parts intermediate between them. Upon these grounds they consider that Fire and not Earth is at the centre of the Universal Sphere; and they have another reason, peculiar to themselves, for this conclusion: they hold that the centre is the most important place in the universe, and that it ought as such to be the most carefully guarded; wherefore they call it the watch of Zeus (Διὸς φυλακήν), and regard it as occupied by Fire (s. 2).
This assumes that what is absolutely (i.e., without subjoining any qualifying adjunct), described asthe centre, is at once centre of the magnitude, centre of the object, and centre of nature. But we ought rather to follow the analogy of animals, where the same point is not the centre of the animal and the centre of the body: the case is the same in the entire Kosmos. Hence the Pythagoreans need not feel any anxiety about the Universe (οὐθὲν αὐτοὺς δεῖ θορυβεῖσθαι περὶ τὸ πᾶν), nor introduce a guard at the centre. They ought rather to enquire where and of what character the middle point is; for that middle point is the true beginning and the honourable. The middle of the place occupied is rather like an end than like a beginning; for that which is limited is the middle, that which limits is the boundary: now that which comprehends and is boundary, is more honourable than that which is bounded; the former is the Essence of the entire compound, the latter is only its Matter (s. 3).
As about the place of the Earth, so also about its motion or rest, philosophers differ. The Pythagoreans and those who do not even place it at the centre, consider it to revolve in a circle, and they consider the Antichthon to revolve in like manner. Some even think it possible that there may be many other bodies carried round the centre in like manner, though invisible to us, by reason of the obstructing body of the Earth. Hence (they say) the eclipses of the moon are more frequent than thoseof the Sun; since not only the Earth, but also each of these unseen bodies, causes the Moon to be eclipsed. For, the Earth not being a point, we on the circumference thereof, even assuming it to occupy the centre, are distant from the centre by the entire hemisphere of the Earth; yet we do not find out that we are not in the centre, and astronomical appearances present themselves to us just as if we were so. Thus it happens (according to these philosophers), the Earth not being in the centre at all: the appearances presented to us are just the same as if we were at the centre.
Again, there are some who (like Plato in Timæus) affirm that the Earth, though situated in the centre, is packed and revolves round the axis stretched across the universe (s. 4).
About the figure of the Earth, there is no less difference of opinion. Some say that it is spherical; others, that it is flat and in shape like a tambourine (τυμπανοειδής). These last adduce as proof, that the Sun, at rising and setting, exhibits a rectilinear section or eclipse of his disk and not a circular one, when partially concealed by the Earth, and becoming invisible under the horizon or visible above the horizon. They do not take proper account of the vast distance of the Sun and the magnitude of his circumference. The segment of a long circle appears from a distance like a straight line. These philosophers further add, that the flat tambourine-like shape must be inferred of necessity from the fact that the Earth remains stationary (s. 5).
Upon this disputed question, a feeling of perplexity comes unavoidably upon every one. It would argue a very irrational mind not to wonder how a small piece of the Earth, if suspended in the air, is carried downward and will not stop of itself, and the larger piece is carried downward more quickly than the smaller; while nevertheless the entire Earth, if suspended in like manner, would not be so carried. In spite of its great weight, it remains stationary (s. 6). But the solutions of this problem which some suggest are more strange and full of perplexity, and it is surprising that they have not been so considered. The Kolophonian Xenophanes affirmed that the lower depths of the Earth were rooted downwards to infinity, in order to escape the troublesome obligation of looking for a reason why it remained stationary. Others say, that the Earth rests upon water, floating thereupon like wood: this is an ancient doctrine promulgated by Thales; as if there were not as much perplexity about the water which supports the Earth, as there is about the Earth itself. For it is not the nature of water to remain suspended, but always to rest upon something (s. 7). Moreover, air is lighter than water, and water lighter than earth; how then can these men think that the substance naturally lighter can lie below the substance naturally heavier? Besides, if it were the nature of the whole Earth to remain resting on water, it must be the nature of each part of the Earth to do the same; but this does not happen: each part of the earth is carried down to the bottom, and the greater part more quickly than the less (s. 8).
All these philosophers carry their researches to a certain point, but not to the bottom of the problem. It is indeed a habit with all of us to conduct our enquiries not with reference to the problem itself, but with reference to our special opponents. If we have no opponent but are conducting our investigations alone, we pursue them as far as that point where we can make no farther objections to ourselves. Whoever therefore intends to investigate completely must take care to make objections to himself upon all the points of objection which really belong to the subject; and this he can only do after having thoroughly surveyed all the differences of opinion and doctrine (s. 9).
The reason why the Earth remains at rest, Anaximenes, Anaxagoras, and Demokritus, declare to be its breadth or flatness (τὸ πλάτος): it does not (they say) divide the air beneath, but covers over the air like a lid (οὐ γὰρ τέμνειν, ἀλλ’ ἐπιπωματίζειν τὸν ἀέρα τὸν κάτωθεν); as we see that flat and spreading bodies usually do, being difficult to be moved and making strong resistance even against the winds. The Earth does the same, through its flatness, against the air beneath, which remains at rest there (in the opinion of these philosophers) because it finds no sufficient place into which to travel, like water in aklepsydra: they also produce many evidences to show that air thus imprisoned, while remaining stationary, can support a heavy weight (s. 10).
Now, in the first place, these men affirm that, unless the shape of the Earth were flat, it would not remain at rest. Yet on their own showing it is not alone the flat shape of the earth which causes it to remain at rest, but rather its magnitude. For the air beneath remainsin situby reason of its vast mass, finding no means of escape through the narrow passage: and the mass of the air is thus vast, because it is imprisoned inside by the great magnitude of the Earth;which effect will be produced in the same manner, even though the Earth be spherical, provided it be of its present magnitude. Moreover, philosophers who hold this opinion about the motion of the Earth, think only of its motion as a whole, and take no account of its parts. For they ought to define at the first step whether bodies have or have not one special mode of motion by nature; and, if none by nature, then whether they have any mode of motion violent or contra-natural. I have already determined this point as well as my powers admitted, and shall therefore assume the results as settled. If there be no special motion natural to bodies, neither will there be any which is contra-natural or violent; and, if there be none either natural or violent, no body will be moved at all. I have already shown that this is a necessary consequence; and, farther, that (upon that supposition) there can be no body even at rest; for rest, like motion, is either natural or contra-natural; and, if there be any special mode of motion which is natural, neither contra-natural motion, nor contra-natural rest, can stand alone (ss. 11-13).
Let us then assume (reasoning on the hypothesis of these philosophers) that the Earth now remains in its present place contrary to nature, and that it was carried into aggregation at the centre by the revolution of the Kosmos (also contrary to nature — καὶ συνῆλθεν ἐπὶ τὸ μέσον φερομένη διὰ τὴν δίνησιν — s. 14). For all those who recognize a generation of the Kosmos assign this revolution as the cause which determined the aggregation of the Earth at the centre, upon the analogy of particles carried round in liquids or in air, where the larger and heavier particles are always carried to the centre of the revolution. They profess thus to know the cause which determined the Earth tocome tothe centre; but what they seek to find out is the cause which determines it to remain there, and upon that they differ: some saying, as has been stated just now, that its breadth and magnitude is the cause; others, with Empedokles, ascribing the fact to the revolution of the Heaven, the extreme velocity of which checks the fall of the Earth downward, just as water in a cup may be whirled rapidly round without falling to the ground. But suppose absence of these two causes: in which direction will the Earth be naturally carried? Not to the centre; for (upon the doctrine which we are now criticising) its motion to the centre, and its remaining at the centre, are both of them contra-natural; but some special mode of motion, natural to the Earth, there must necessarily be. Is this upward, or downward, or in what other direction? If there be no greater tendency downward than upward, and if the air above does not hinder the Earth from tending upward, neither will the air beneath hinder it from tending downwards: the same causes produce the same effects, operating on the same matter (ss. 14, 15).
A farther argument becomes applicable, when we are reasoning against Empedokles. When the four elements were first separated out of their confused huddle by the influence of Contention, what was the cause for the Earth to remain still andin situ? Empedokles cannot claim to introduce then the agency of the cosmical revolution. Moreover, it is strange that he should not have reflected that in the first instance the particles and fragments of the Earth were carried to the centre. But what is the cause now that every thing having weight is carried towards the Earth? It cannot be the revolution of the Heaven which brings these things nearer to us (s. 16).
Again, Fire is carried upward. What is the cause of this? The revolution of the Heaven cannot cause it. But, if it be the nature of fire to be carried in one certain direction, it must be equally the nature of Earth to be carried in one certain direction. Light and heavy, also, are not discriminated by the heavenly revolution. There are matters originally heavy, and matters originally light: the former are carried to the centre, the latter to the circumference, each by its own special motion. Even prior to the heavenly revolution there existed things intrinsically light and intrinsically heavy; which are discriminated by certain attributes — a certain natural mode of motion and a certain place. In infinite space, there can be no upward and downward; and it is by this (local distinction) that light and heavy are discriminated (ss. 17, 18).
While most philosophers insist upon the causes just noticed why the Earth remains stationary where it is, there are others, like Anaximander, among the ancients, who say that it remains so because of its likeness or equality (διὰ τὴν ὁμοιότερα — equal tendency in all directions). That which is situated in the centre (they say) and which has like relation to the extreme parts (i.e., like toallthe extreme parts) ought not to be carried any more upward or downward or sideways; and it cannot be moved in opposite directions at once; so that it remains stationary by necessity (s. 19).
This doctrine is ingenious, but nottrue. For the property affirmed is noway peculiar to the Earth: the affirmation is, that every thing which is placed at the centre must of necessity remain there; so that Fire also would remain there at rest, as well as Earth. But this necessity must be denied. For it is shown by observation that the Earth not only remains at the centre, but is carried to the centre; since each part of it is carried thither, and, whithersoever the parts are carried, the whole is carried necessarily to the same point. The peculiar property of the earth therefore is, not (as this hypothesis declares) to have like relation to all the extreme parts — for that is common to all the elements — but to be carried towards the centre (ss. 20, 21).
Moreover, it is absurd to investigate why the Earth remains at the centre, and not to investigate equally why Fire remains at the extremity. For, if you explain this last by saying that Fire has its natural place at the extremity, the Earth must have its natural place somewhere else. If the centre be not the natural place of the Earth, and if the Earth remains there through like tendency in all directions, like the hair in equal tension or the man both hungry and thirsty between food and drink, you must equally assign the reason why Fire remains at the extremity. It is singular too that you should try to explain only theremaining at rest(μονῆς) of the Earth, and not also seek to explain the natural current (φορά) — why Earth is carried downward, and Fire upward, when there is no opposing force (s. 22).
Nor can it be admitted that the doctrine is true. Thus much indeed is true by accident — that every thing which has no greater obligation to be moved in this direction than in that, must necessarily remain at the centre. But this is true only so long as it remains a compact whole; for, according to the theory which we are discussing, it will not remain stationary, but will be moved: not indeed as a whole, but dispersed into parts (s. 23: ἀλλὰ μὴν οὐδὲ ἀληθές ἐστι τὸ λεγόμενον. κατὰ συμβεβηκὸς μέντοι τοῦτό γε ἀληθές, ὡς ἀναγκαῖον μένειν ἐπὶ τοῦ μέσου πᾶν, ᾧ μηθὲν μᾶλλον δεῦρο ἡ δεῦρο κινεῖσθαι προσήκει. ἀλλὰ διά γε τοῦτον τὸν λόγον οὐ μενεῖ ἀλλὰ κινηθήσεται· οὐ μέντοι ὅλον, ἀλλὰ διεσπασμένον. — I understand κατὰ συμβεβηκός to mean, subject to the condition of its remaining a compact whole). For the same reasoning would apply to Fire as well as to Earth: it would prove that Fire, if placed at the centre, will remain there just as much as Earth, because Fire will have like relation to each point of the extreme periphery. Yet nevertheless it will (not remain at the centre, but will) be carried away, if not impeded, as we observe that it is carried in fact, to the periphery; only not all to one and the same point of the periphery, but corresponding portions of the Fire to corresponding portions of the periphery: I mean, that the fourth part (e.g.) of the Fire will be carried to the fourth part of the periphery; for a point is no real part of bodies (οὐθὲν γὰρ στιγμὴ τῶν σωμάτων ἐστίν). This is the only necessary consequence flowing from the principle of likeness of relation. As, if supposed to be put all together at the centre, it would contract from a larger area into a smaller, so, when carried away from the centre to the different parts of the periphery, it would become rarer and would expand from a smaller area into a larger. In like manner the Earth also would be moved away from the centre, if you reason upon this principle of likeness of relation, and if the centre were not the place belonging to it by nature (s. 24).
CH. 14. — Having thus reported the suppositions of others respecting the figure, place, rest and motion, of the Earth, I shall now deliver my own opinion, first, whether it is in motion or at rest; for some philosophers, as I have said, regard it as one of the stars (and therefore not in the centre, but moving round the centre — the Pythagorean theory); others (as Plato), though they place it in the centre, consider it to be packed and moved round the middle of the axis of the Kosmos (οἱ δὲ ἐπὶ τοῦ μέσου θέντες, εἰλεῖσθαι καὶ κινεῖσθαί φασι περὶ τὸν μέσον πόλον).
That neither of these hypotheses is possible, we shall perceive if we take as our point of departure — That, if the Earth be carried round, whether in the centre or apart from the centre, such motion must necessarily be violent or contra-natural. Such motion does not belong naturally to the Earth itself; for, if such were the fact, it would belong equally to each portion of the Earth, whereas we see that all these portions are carried in a straight line to the centre. Being thus violent or contra-natural, it cannot possibly be eternal. But the order of the Kosmos is eternal. Besides, all the bodies which are carried round in a circular revolution (all except the First or Outermost Sphere — the Aplanês) appear to observation as lagging behind and as being moved in more than one current. The like ought to happen with the Earth, if moved round, whether on the centre or apart from the centre: it ought to be moved in two currents; and,as a consequence thereof, there ought to be side-motions and back-turnings of the stars fastened in their sphere. But we see by observation that this does not happen; and that the same stars always rise and set at the same places of the Earth (s. 1).
Farthermore, the natural current both of the entire Earth and of each of its parts is towards the middle of the universe: this is the reason why it is at the centre, even though it happens to be actually there at present (διὰ τοῦτο γὰρ, κἂν εἰ τυγχάνει κειμένη νῦν ἐπὶ τοῦ κέντρου — he means that though actually there, it remains there not through any force of inertia or other cause, but because it has a natural current towards the centre). You might start a doubt, indeed, since the centre of the Universe coincides with the centre of the Earth, to which of the two it is that the current of heavy bodies naturally tends: whether they tend thereto because it is the centre of the Universe, or because it is the centre of the Earth. We must however necessarily suppose the former; since Fire and light bodies, whose current is the contrary of the current of heavy bodies, are carried to the extreme periphery of the Universe, or of that place which comprehends and surrounds the centre of the Universe (ss. 2, 3). But it happens (συμβέβηκε: it is an accompanying fact) that the same point is centre of the Universe and centre of the Earth; accordingly heavy bodies are carried by accident (κατὰ συμβεβηκός — by virtue of this accompanying fact) to the centre of the Earth; and the proof that they are carried to this same point is, that their lines of direction are not parallel but according to similar angles (s. 4). That the Earth therefore is at the centre, and that it is at rest, we may see by the foregoing reasons, as well as by the fact, that stones thrown upwards to ever so great a height, are carried back in the same line of direction to the same point (s. 5).
We may see farther the cause why the Earth remains at rest. For, if its natural current be from all directions towards the centre, as observation shows, and that of Fire from the centre to the periphery, — no portion of it can possibly be carried away from the centre, except by violence. For to one body belongs one current of motion, and to a simple body a simple current — not the two opposite currents; and the currentfromthe centre is opposite to the currenttothe centre. If, therefore, it be impossible for any portion of the Earth to be carried in a direction away from the centre, it is yet more impossible for the whole Earth to be so; for the natural current of each part is the same as that of the whole. Accordingly, since the Earth cannot be moved except by a superior force or violence, it must necessarily remain stationary at the centre (s. 6). The same conclusion is confirmed by what we learn from geometers respecting astronomy; for all the phenomena of the Heavens — the changes in figure, order, and arrangement of the stars — take place as if the Earth were in the centre (s. 7).
The figure of the Earth is necessarily spherical. For each of its parts has gravity, until it reaches the centre; and the lesser part, pushed forward by the greater, cannot escape laterally, but must become more and more squeezed together, one part giving place to the other, until the centre itself is reached. We must conceive what is here affirmed as occurring in a manner like what some of the ancient physical philosophers tell us, except thattheyascribe the downward current to an extraneous force; whereas we think it better to state the truth, and to say that it occurs becauseby natureall heavy bodies are carried towards the centre. Since, therefore, the preliminary Chaos or hotchpotch existed in power (or with its inherent powers existing though not exercised), the elements (those which had gravity), were carried from all sides equally towards the centre (ἐν δυνάμει οὖν ὄντος τοῦ μίγματος, τὰ διακρινόμενα ἐφέρετο ὁμοίως πάντοθεν πρὸς τὸ μέσον — this is an allusion to the doctrine of Anaxagoras); indeed, whether brought together at the centre equally from all the periphery or in any other manner, the result will be the same. If we suppose particles to be brought together at the centre equally from all sides, it is plain that the mass so formed will be regular and spherical; and, even if not equally from all sides, this will make no difference in the reasoning; for, since all portions of the mass have weight or tend to the centre, the larger portions will necessarily push the lesser before them as far as the centre (ss. 8, 9).
A difficulty here presents itself, which may be solved upon the same principles. The Earth being spherical, and at the centre, suppose that a vast additional weight were applied to either of its hemispheres. In that case, the centre of the Universe, and the centre of the Earth, would cease to coincide: either, therefore, the Earth will not remain at the centre; or, if it would still remain at rest, while not occupying the centre, it is in its nature to be moved even now (s. 10: ὥστε ἢ οὐ μενεῖ ἐπὶ τοῦ μέσου, ἢ εἴπερ ἠρεμήσει γε καὶ μὴ τὸ μέσον ἔχουσα ᾖ, πέφυκε κινεῖσθαι καὶ νῦν) —i.e., if the Earthcanbe at rest when not at thecentre, we must infer that the centre is not its natural place, and therefore that its nature will be to be moved from the centre towards that natural place wherever situated).
Such is a statement of the difficulty; but we shall see that it may be cleared up with a little attention. We must distinguish what we mean when we affirm that every particle having weight is carried towards the centre. We clearly do not mean that it will be so carried until the particles farthest from the centre shall touch the centre. We mean that the greater mass must press with preponderating force (δεῖ κρατεῖν τὸ πλεῖον ἕως ἂν λάβῃ τῷ αὑτοῦ μέσῳ τὸ μέσον) until its centre grasps the centre of the universe; up to this point its gravity will last; and this is equally true about any clod of earth as about the whole earth: large or small size makes no difference. Whether the whole Earth were carried in a mass from any given position, or whether it were carried in separate particles, in either case it would be carried onward until it embraced the centre equally on all sides; the smaller parts being equalized to the greater in gravitating tendency because they are pushed forward by the greater (ἀνισαζομένων τῶν ἐλαττόνων ὑπὸ τῶν μειζόνων τῇ προώσει — s. 11). If, therefore, the Earth was ever generated, it must have been generated in this manner, and must thus acquire a spherical figure; and, even if it be ungenerable and stationary from everlasting, we must conceive its figure to be that which it would have acquired, if it had been generable and generated from the first (εἴτε ἀγέννητος ἀεὶ μένουσα, τὸν αὐτὸν τρόπον ἔχειν, ὅνπερ κἂν εἰ γιγνομένη τὸ πρῶτον ἐγένετο). That it must be spherical, we see not only from this reasoning, but also because all heavy bodies are carried towards it, not in parallel lines but, in equal angles. This is what naturally happens with what is either actually spherical, or by nature spherical. Now we ought to call every thing such as it by nature wishes to become and to be: we ought not to call it such as it is by force and contrary to nature (s. 12).
The same conclusion is established by the sensible facts within our observation. If the Earth had been of any other than spherical figure, the eclipses of the Moon would not have projected on the Sun the outlines which we now see. The moon in her configurations throughout the month takes on every variety of outline — rectilinear, double convex, and hollow. But in her eclipses the distinguishing line is always convex. Now this must necessarily be occasioned by the circumference of the Earth being spherical, since the eclipses of the Moon arise from the interposition of the Earth (s. 13).
Farthermore, we see from the visible phenomena of the stars not only that the Earth is spherical, but also that its magnitude is not great. For, when we change our position a little as observers, either to the north or to the south, we find the celestial horizon to be manifestly different. The stars at the zenith are greatly changed, and the same stars do not appear: some stars are visible in Egypt and Cyprus, but become invisible when we proceed farther north; and those which are constantly visible in the northern regions, are found to be not constantly visible, but to set, when the observer is in Egypt or Cyprus. The bulk of the Earth must therefore be small, when a small change of position is made so soon manifest to us (s. 14). Hence those who hold that the regions near the pillars of Herakles join on with India and that the ocean eastward and westward is one and the same, must not be supposed to talk extravagantly (μὴ λίαν ὑπολαμβάνειν ἄπιστα δοκεῖν): they infer this from the presence of elephants alike at both extremities. Geometers who try to calculate the magnitude of the Earth, affirm that its circumference is 400,000 stadia.
It follows necessarily from all these reasonings, that the body of the Earth is not only of spherical form, but also not large compared with the magnitude of the other Stars (ss. 15, 16).