Name: On the Heavens, Book IV
Author: Aristotle

Moraux (Budé, 1965) · Stocks (1922)

Stocks (1922)

Greek line numbers are exact. The translations carry no Bekker numbers of their own, so those beside the English are aligned to the Greek: upright = fixed (anchored to this point in the text), italic grey = approximate (interpolated estimate).

Book 4,Chapter 1 (307b28–308a33)

307b

Περὶ δὲ βαρέος καὶ κούφου, τί τ' ἐστὶν ἑκάτερον καὶ τίς

ἡ φύσις αὐτῶν, σκεπτέον, καὶ διὰ τίν' αἰτίαν ἔχουσι τὰς

30 δυνάμεις ταύτας. Ἔστι γὰρ ἡ περὶ αὐτῶν θεωρία τοῖς περὶ

κινήσεως λόγοις οἰκεία· βαρὺ γὰρ καὶ κοῦφον τῷ δύνασθαι

κινεῖσθαι φυσικῶς πως λέγομεν. (Ταῖς δὲ ἐνεργείαις ὀνόματ'

αὐτῶν οὐ κεῖται, πλὴν εἴ τις οἴοιτο τὴν ῥοπὴν εἶναι τοιοῦτον.)

We have now to consider the terms 'heavy' and 'light'. We must ask what the bodies so called are, how they are constituted, and what is the reason of their possessing these powers. The consideration 30of these questions is a proper part of the theory of movement, since we call things heavy and light because they have the power of being moved naturally in a certain way. The activities corresponding to these powers have not been given any name, unless it is thought that 'impetus' is such a name.

308a

1 Διὰ δὲ τὸ τὴν φυσικὴν μὲν εἶναι πραγματείαν περὶ

κίνησιν, ταῦτα δ' ἔχειν ἐν ἑαυτοῖς οἷον ζώπυρ' ἄττα κινήσεως,

πάντες μὲν χρῶνται ταῖς δυνάμεσιν αὐτῶν, οὐ μὴν διωρίκασί

γε, πλὴν ὀλίγων. Ἰδόντες οὖν πρῶτον τὰ παρὰ τῶν ἄλλων

5 εἰρημένα, καὶ διαπορήσαντες ὅσα πρὸς τὴν σκέψιν ταύτην

διελεῖν ἀναγκαῖον, οὕτω καὶ τὸ φαινόμενον ἡμῖν εἴπωμεν

περὶ αὐτῶν. Λέγεται δὴ τὸ μὲν ἁπλῶς βαρὺ καὶ κοῦφον,

τὸ δὲ πρὸς ἕτερον· τῶν γὰρ ἐχόντων βάρος φαμὲν τὸ μὲν

εἶναι κουφότερον, τὸ δὲ βαρύτερον, οἷον ξύλου χαλκόν. Περὶ

10 μὲν οὖν τῶν ἁπλῶς λεγομένων οὐδὲν εἴρηται παρὰ τῶν πρότερον,

περὶ δὲ τῶν πρὸς ἕτερον· οὐ γὰρ λέγουσι τί ἐστι τὸ

βαρὺ καὶ τί τὸ κοῦφον, ἀλλὰ τί τὸ βαρύτερον καὶ κουφότερον

ἐν τοῖς ἔχουσι βάρος. Μᾶλλον δ' ἔσται δῆλον ὃ

λέγομεν ὧδε. Τὰ μὲν γὰρ ἀεὶ πέφυκεν ἀπὸ τοῦ μέσου φέρεσθαι,

15 τὰ δ' ἀεὶ πρὸς τὸ μέσον. Τούτων δὲ τὸ μὲν ἀπὸ

τοῦ μέσου φερόμενον ἄνω λέγω φέρεσθαι, κάτω δὲ τὸ πρὸς

τὸ μέσον. Ἄτοπον γὰρ τὸ μὴ νομίζειν εἶναί τι ἐν τῷ οὐρανῷ

τὸ μὲν ἄνω τὸ δὲ κάτω, καθάπερ τινὲς ἀξιοῦσιν· οὐ γὰρ εἶναι

τὸ μὲν ἄνω τὸ δὲ κάτω φασίν, εἴπερ πάντῃ ὅμοιός ἐστι,

20 καὶ πανταχόθεν ἀντίπους ἔσται πορευόμενος ἕκαστος αὐτὸς

αὑτῷ. Ἡμεῖς δὲ τὸ τοῦ παντὸς ἔσχατον ἄνω λέγομεν, ὃ καὶ

κατὰ τὴν θέσιν ἐστὶν ἄνω καὶ τῇ φύσει πρῶτον· ἐπεὶ δ' ἐστί

τι τοῦ οὐρανοῦ ἔσχατον καὶ μέσον, δῆλον ὅτι ἔσται καὶ ἄνω

καὶ κάτω, ὥσπερ καὶ οἱ πολλοὶ λέγουσι, πλὴν οὐχ ἱκανῶς.

25 Τούτου δ' αἴτιον ὅτι νομίζουσιν οὐχ ὅμοιον εἶναι πάντῃ τὸν

οὐρανόν, ἀλλ' ἓν εἶναι μόνον τὸ ὑπὲρ ἡμᾶς ἡμισφαίριον, ἐπεὶ

προσυπολαβόντες καὶ κύκλῳ τοιοῦτον, καὶ τὸ μέσον ὁμοίως

ἔχειν πρὸς ἅπαν, τὸ μὲν ἄνω φήσουσιν εἶναι, τὸ δὲ μέσον

κάτω. Ἁπλῶς μὲν οὖν κοῦφον λέγομεν τὸ ἄνω φερόμενον καὶ

30 πρὸς τὸ ἔσχατον, βαρὺ δὲ ἁπλῶς τὸ κάτω καὶ πρὸς τὸ

μέσον· πρὸς ἄλλο δὲ κοῦφον καὶ κουφότερον, ὅτε, δυοῖν ἐχόντων

βάρος καὶ τὸν ὄγκον ἴσον, κάτω φέρεται θάτερον φύσει

θᾶττον.

1But because the inquiry into nature is concerned with movement, and these things have in themselves some spark (as it were) of movement, all inquirers avail themselves of these powers, though in all but a few cases without exact discrimination. We must then first look at whatever others have said, 5and formulate the questions which require settlement in the interests of this inquiry, before we go on to state our own view of the matter.
Language recognizes (a) an absolute, (b) a relative heavy and light. Of two heavy things, such as wood and bronze, we say that the one is relatively light, the other relatively heavy. Our predecessors have not dealt at all with 10the absolute use, of the terms, but only with the relative. I mean, they do not explain what the heavy is or what the light is, but only the relative heaviness and lightness of things possessing weight. This can be made clearer as follows. There are things whose constant nature it is to move away from the centre, while others move constantly towards the centre; and of 15these movements that which is away from the centre I call upward movement and that which is towards it I call downward movement. (The view, urged by some, that there is no up and no down in the heaven, is absurd. There can be, they say, no up and no down, since the universe is similar every way, and from any point on the earth's surface a man by advancing far enough will 20come to stand foot to foot with himself. But the extremity of the whole, which we call 'above', is in position above and in nature primary. And since the universe has an extremity and a centre, it must clearly have an up and down. Common usage is thus correct, though inadequate. And the reason of its inadequacy is that men think that the universe is not similar every way. 25They recognize only the hemisphere which is over us. But if they went on to think of the world as formed on this pattern all round, with a centre identically related to each point on the extremity, they would have to admit that the extremity was above and the centre below.) By absolutely light, then, we mean that which moves upward or to the extremity, and by absolutely 30heavy that which moves downward or to the centre. By lighter or relatively light we mean that one, of two bodies endowed with weight and equal in bulk, which is exceeded by the other in the speed of its natural downward movement.

Book 4,Chapter 2 (308a34–310a15)

Τῶν δὴ πρότερον ἐλθόντων ἐπὶ τὴν περὶ τούτων σκέψιν

35 σχεδὸν οἱ πλεῖστοι περὶ τῶν οὕτω βαρέων καὶ κούφων εἰρήκασι

μόνον, ὅσων ἀμφοτέρων ἐχόντων βάρος θάτερόν ἐστι

Those of our predecessors who have entered upon this inquiry have for the most part spoken of light and heavy things only in the sense in 35which one of two things both endowed with weight is said to be the lighter.

308b

1 κουφότερον· οὕτω δὲ διελθόντες οἴονται διωρίσθαι καὶ περὶ

τοῦ ἁπλῶς κούφου καὶ βαρέος· ὁ δὲ λόγος αὐτοῖς οὐκ ἐφαρμόττει.

Δῆλον δ' ἔσται τοῦτο μᾶλλον προελθοῦσιν. Λέγουσι

γὰρ τὸ κουφότερον καὶ βαρύτερον οἱ μὲν ὥσπερ ἐν τῷ Τιμαίῳ

5 τυγχάνει γεγραμμένον, βαρύτερον μὲν τὸ ἐκ πλειόνων

τῶν αὐτῶν συνεστός, κουφότερον δὲ τὸ ἐξ ἐλαττόνων,

ὥσπερ μολίβδου μόλιβδος ὁ πλείων βαρύτερος καὶ χαλκοῦ

χαλκός. Ὁμοίως δὲ καὶ τῶν ἄλλων τῶν ὁμοειδῶν ἕκαστον·

ἐν ὑπεροχῇ γὰρ τῶν ἴσων μορίων βαρύτερον ἕκαστόν ἐστιν. Τὸν

10 αὐτὸν δὲ τρόπον καὶ ξύλου μόλιβδόν φασιν· ἔκ τινων γὰρ

τῶν αὐτῶν εἶναι πάντα τὰ σώματα καὶ μιᾶς ὕλης, ἀλλ'

οὐ δοκεῖν. Οὕτω δὴ διωρισμένων οὐκ εἴρηται περὶ τοῦ ἁπλῶς

κούφου καὶ βαρέος· νῦν γὰρ τὸ μὲν πῦρ ἀεὶ κοῦφον καὶ ἄνω

φέρεται, ἡ δὲ γῆ καὶ τὰ γεηρὰ πάντα κάτω καὶ πρὸς τὸ

15 μέσον. Ὥστ' οὐ δι' ὀλιγότητα τῶν τριγώνων, ἐξ ὧν συνεστάναι

φασὶν ἕκαστον αὐτῶν, τὸ πῦρ ἄνω φέρεσθαι πέφυκεν· τό

τε γὰρ πλεῖον ἧττον ἂν ἐφέρετο καὶ βαρύτερον ἦν ἐκ

πλειόνων ὂν τριγώνων. Νῦν δὲ φαίνεται τοὐναντίον· ὅσῳ γὰρ

ἂν ᾖ πλεῖον, κουφότερόν ἐστι καὶ ἄνω φέρεται θᾶττον. Καὶ

20 ἄνωθεν δὲ κάτω τὸ ὀλίγον οἰσθήσεται θᾶττον πῦρ, τὸ δὲ

πολὺ βραδύτερον. Πρὸς δὲ τούτοις, ἐπεὶ τὸ μὲν ἐλάσσω

ἔχον τὰ ὁμογενῆ κουφότερον εἶναί φασι, τὸ δὲ πλείω βαρύτερον,

ἀέρα δὲ καὶ ὕδωρ καὶ πῦρ ἐκ τῶν αὐτῶν εἶναι

τριγώνων, ἀλλὰ διαφέρειν ὀλιγότητι καὶ πλήθει, διὸ τὸ

25 μὲν αὐτῶν εἶναι κουφότερον τὸ δὲ βαρύτερον, ἔσται τι πλῆθος

ἀέρος ὃ βαρύτερον ὕδατος ἔσται. Συμβαίνει δὲ πᾶν τοὐναντίον·

ἀεί τε γὰρ ὁ πλείων ἀὴρ ἄνω φέρεται μᾶλλον,

καὶ ὅλως ὁτιοῦν μέρος ἀέρος ἄνω φέρεται ἐκ τοῦ ὕδατος. Οἱ

μὲν οὖν τοῦτον τὸν τρόπον περὶ κούφου καὶ βαρέος διώρισαν·

30 τοῖς δ' οὐχ ἱκανὸν ἔδοξεν οὕτω διελεῖν, ἀλλὰ καίπερ ὄντες

ἀρχαιότεροι ταῖς ἡλικίαις καινοτέρως ἐνόησαν περὶ τῶν

νῦν λεχθέντων. Φαίνεται γὰρ ἔνια τὸν ὄγκον μὲν ἐλάττω

τῶν σωμάτων, ὄντα δὲ βαρύτερα. Δῆλον οὖν ὡς οὐχ ἱκανὸν

τὸ φάσκειν ἐξ ἴσων συγκεῖσθαι τῶν πρώτων τὰ ἰσοβαρῆ·

35 ἴσα γὰρ ἂν ἦν τὸν ὄγκον. Τὰ δὲ πρῶτα καὶ ἄτομα τοῖς

μὲν ἐπίπεδα λέγουσιν ἐξ ὧν συνέστηκε τὰ βάρος ἔχοντα

1And this treatment they consider a sufficient analysis also of the notions of absolute heaviness, to which their account does not apply. This, however, will become clearer as we advance. One use of the terms 'lighter' and 'heavier' is that which is set forth in writing in the Timaeus, that the body 5which is composed of the greater number of identical parts is relatively heavy, while that which is composed of a smaller number is relatively light. As a larger quantity of lead or of bronze is heavier than a smaller-and this holds good of all homogeneous masses, the superior weight always depending upon a numerical superiority of equal parts-in precisely the same way, they 10assert, lead is heavier than wood. For all bodies, in spite of the general opinion to the contrary, are composed of identical parts and of a single material. But this analysis says nothing of the absolutely heavy and light. The facts are that fire is always light and moves upward, while earth and all earthy things move downwards or towards the centre. It cannot then be the 15fewness of the triangles (of which, in their view, all these bodies are composed) which disposes fire to move upward. If it were, the greater the quantity of fire the slower it would move, owing to the increase of weight due to the increased number of triangles. But the palpable fact, on the contrary, is that the greater the quantity, the lighter the mass is and the quicker 20its upward movement: and, similarly, in the reverse movement from above downward, the small mass will move quicker and the large slower. Further, since to be lighter is to have fewer of these homogeneous parts and to be heavier is to have more, and air, water, and fire are composed of the same triangles, the only difference being in the number of such parts, which must 25therefore explain any distinction of relatively light and heavy between these bodies, it follows that there must be a certain quantum of air which is heavier than water. But the facts are directly opposed to this. The larger the quantity of air the more readily it moves upward, and any portion of air without exception will rise up out of the water.
So much for one view of the 30distinction between light and heavy. To others the analysis seems insufficient; and their views on the subject, though they belong to an older generation than ours, have an air of novelty. It is apparent that there are bodies which, when smaller in bulk than others, yet exceed them in weight. It is therefore obviously insufficient to say that bodies of equal weight are composed 35of an equal number of primary parts: for that would give equality of bulk.

309a

1 τῶν σωμάτων, ἄτοπον τὸ φάναι· τοῖς δὲ στερεὰ μᾶλλον

ἐνδέχεται λέγειν τὸ μεῖζον εἶναι βαρύτερον αὐτῶν. Τῶν δὲ

συνθέτων, ἐπειδήπερ οὐ φαίνεται τοῦτον ἕκαστον ἔχειν τὸν

τρόπον, ἀλλὰ πολλὰ βαρύτερα ὁρῶμεν ἐλάττω τὸν ὄγκον

5 ὄντα, καθάπερ ἐρίου χαλκόν, ἕτερον τὸ αἴτιον οἴονταί τε

καὶ λέγουσιν ἔνιοι· τὸ γὰρ κενὸν ἐμπεριλαμβανόμενον κουφίζειν

τὰ σώματά φασι καὶ ποιεῖν ἔστιν ὅτε τὰ μείζω

κουφότερα· πλεῖον γὰρ ἔχειν κενόν. Διὰ τοῦτο γὰρ καὶ τὸν

ὄγκον εἶναι μείζω συγκείμενα πολλάκις ἐξ ἴσων στερεῶν ἢ

10 καὶ ἐλαττόνων. Ὅλως δὲ καὶ παντὸς αἴτιον εἶναι τοῦ κουφοτέρου

τὸ πλεῖον ἐνυπάρχειν κενόν. Λέγουσι μὲν οὖν τοῦτον τὸν

τρόπον, ἀνάγκη δὲ προσθεῖναι τοῖς οὕτω διορίζουσι μὴ μόνον

τὸ κενὸν ἔχειν πλεῖον, ἂν ᾖ κουφότερον, ἀλλὰ καὶ τὸ στερεὸν

ἔλαττον· εἰ γὰρ ὑπερέξει τῆς τοιαύτης ἀναλογίας, οὐκ

15 ἔσται κουφότερον. Διὰ γὰρ τοῦτο καὶ τὸ πῦρ εἶναί φασι κουφότατον,

ὅτι πλεῖστον ἔχει κενόν. Συμβήσεται οὖν μικροῦ

πυρὸς πολὺν χρυσὸν πλεῖον ἔχοντα τὸ κενὸν εἶναι κουφότερον,

εἰ μὴ καὶ στερεὸν ἕξει πολλαπλάσιον· ὥστε τοῦτο λεκτέον.

Ἔνιοι μὲν οὖν τῶν μὴ φασκόντων εἶναι κενὸν οὐδὲν διώρισαν

20 περὶ κούφου καὶ βαρέος, οἷον Ἀναξαγόρας καὶ Ἐμπεδοκλῆς·

οἱ δὲ διορίσαντες μέν, οὐ φάσκοντες δὲ εἶναι κενόν,

οὐδὲν εἶπον διὰ τί τὰ μὲν ἁπλῶς κοῦφα τὰ δὲ βαρέα τῶν

σωμάτων, καὶ φέρεται τὰ μὲν ἀεὶ ἄνω τὰ δὲ κάτω, οὐδὲ

περὶ τοῦ ἔνια μείζω τὸν ὄγκον ὄντα κουφότερα τῶν ἐλαττόνων

25 εἶναι σωμάτων οὐδὲν ἐπεμνήσθησαν, οὐδὲ δῆλον πῶς

ἐκ τῶν εἰρημένων ὁμολογούμενα τοῖς φαινομένοις συμβήσεται

λέγειν αὐτοῖς. Ἀναγκαῖον δὲ καὶ τοῖς περὶ τῆς τοῦ πυρὸς

κουφότητος αἰτιωμένοις τὸ πολὺ κενὸν ἔχειν σχεδὸν ἐν ταῖς

αὐταῖς ἐνέχεσθαι δυσχερείαις. Ἔλαττον μὲν γὰρ ἕξει στερεὸν

30 τῶν ἄλλων σωμάτων, καὶ τὸ κενὸν πλεῖον· ἀλλ' ὅμως ἔσται

τι πυρὸς πλῆθος ἐν ᾧ τὸ στερεὸν καὶ τὸ πλῆρες ὑπερβάλλει

τῶν περιεχομένων στερεῶν ἔν τινι μικρῷ πλήθει γῆς. Ἐὰν δὲ

φῶσι καὶ τὸ κενόν, πῶς διοριοῦσι τὸ ἁπλῶς βαρύ; Ἢ γὰρ

τῷ πλεῖον στερεὸν ἔχειν ἢ τῷ ἔλαττον κενόν. Εἰ μὲν οὖν τοῦτο

1Those who maintain that the primary or atomic parts, of which bodies endowed with weight are composed, are planes, cannot so speak without absurdity; but those who regard them as solids are in a better position to assert that of such bodies the larger is the heavier. But since in composite bodies the weight obviously 5does not correspond in this way to the bulk, the lesser bulk being often superior in weight (as, for instance, if one be wool and the other bronze), there are some who think and say that the cause is to be found elsewhere. The void, they say, which is imprisoned in bodies, lightens them and sometimes makes the larger body the lighter. The reason is that there is more void. And this would 10also account for the fact that a body composed of a number of solid parts equal to, or even smaller than, that of another is sometimes larger in bulk than it. In short, generally and in every case a body is relatively light when it contains a relatively large amount of void. This is the way they put it themselves, but their account requires an addition. Relative lightness must depend not only 15on an excess of void, but also an a defect of solid: for if the ratio of solid to void exceeds a certain proportion, the relative lightness will disappear. Thus fire, they say, is the lightest of things just for this reason that it has the most void. But it would follow that a large mass of gold, as containing more void than a small mass of fire, is lighter than it, unless it also contains many 20times as much solid. The addition is therefore necessary.
Of those who deny the existence of a void some, like Anaxagoras and Empedocles, have not tried to analyse the notions of light and heavy at all; and those who, while still denying the existence of a void, have attempted this, have failed to explain why there are bodies which are absolutely heavy and light, or in other words why some 25move upward and others downward. The fact, again, that the body of greater bulk is sometimes lighter than smaller bodies is one which they have passed over in silence, and what they have said gives no obvious suggestion for reconciling their views with the observed facts.
But those who attribute the lightness of fire to its containing so much void are necessarily involved in practically the 30same difficulties. For though fire be supposed to contain less solid than any other body, as well as more void, yet there will be a certain quantum of fire in which the amount of solid or plenum is in excess of the solids contained in some small quantity of earth. They may reply that there is an excess of void also.

309b

1 φήσουσιν, ἔσται τι πλῆθος γῆς οὕτως ὀλίγον ἐν ᾧ στερεὸν

ἔσται ἔλαττον ἢ ἐν πολλῷ πλήθει πυρός. Ὁμοίως δὲ κἂν τῷ κενῷ

διορίσωσιν, ἔσται τι κουφότερον τοῦ ἁπλῶς κούφου καὶ φερομένου

ἀεὶ ἄνω αὐτὸ φερόμενον ἀεὶ κάτω. Τοῦτο δὲ ἀδύνατον·

5 τὸ γὰρ ἁπλῶς κοῦφον ἀεὶ κουφότερον τῶν ἐχόντων βάρος

καὶ κάτω φερομένων, τὸ δὲ κουφότερον οὐκ ἀεὶ κοῦφον διὰ

τὸ λέγεσθαι καὶ ἐν τοῖς ἔχουσι βάρος ἕτερον ἑτέρου κουφότερον,

οἷον γῆς ὕδωρ. Ἀλλὰ μὴν οὐδὲ τῷ τὸ κενὸν ἀνάλογον

ἔχειν πρὸς τὸ πλῆρες ἱκανὸν λῦσαι τὴν λεγομένην νῦν ἀπορίαν.

10 Συμβήσεται γὰρ καὶ τοῦτον τὸν τρόπον λέγουσιν ὡσαύτως

τὸ ἀδύνατον. Ἐν γὰρ τῷ πλείονι πυρὶ καὶ ἐν τῷ ἐλάττονι

τὸν αὐτὸν ἕξει λόγον τὸ στερεὸν πρὸς τὸ κενόν. Φέρεται

δέ γε θᾶττον τὸ πλεῖον ἄνω πῦρ τοῦ ἐλάττονος, καὶ κάτω

δὲ πάλιν ὡσαύτως ὁ πλείων χρυσὸς καὶ ὁ μόλιβδος· ὁμοίως

15 δὲ καὶ τῶν ἄλλων ἕκαστον τῶν ἐχόντων βάρος. Οὐκ ἔδει δὲ

τοῦτο συμβαίνειν, εἴπερ τούτῳ διώρισται τὸ βαρὺ καὶ κοῦφον.

Ἄτοπον δὲ καὶ εἰ διὰ τὸ κενὸν μὲν ἄνω φέρονται, τὸ δὲ κενὸν

αὐτὸ μή. Ἀλλὰ μὴν εἴ γε τὸ μὲν κενὸν ἄνω πέφυκε

φέρεσθαι, κάτω δὲ τὸ πλῆρες, καὶ διὰ τοῦτο τοῖς ἄλλοις

20 αἴτια τῆς φορᾶς ἑκατέρας, οὐθὲν περὶ τῶν συνθέτων ἔδει

σκοπεῖν διὰ τί τὰ μὲν κοῦφα τὰ δὲ βαρέα τῶν σωμάτων,

ἀλλὰ περὶ τούτων αὐτῶν εἰπεῖν διὰ τί τὸ μὲν κοῦφον, τὸ δ'

ἔχει βάρος, ἔτι δὲ τί τὸ αἴτιον τοῦ μὴ διεστάναι τὸ πλῆρες

καὶ τὸ κενόν. Ἄλογον δὲ καὶ τὸ χώραν τῷ κενῷ ποιεῖν, ὥςπερ

25 οὐκ αὐτὸ χώραν τινὰ οὖσαν· ἀναγκαῖον δ', εἴπερ κινεῖται

τὸ κενόν, εἶναι αὐτοῦ τινα τόπον, ἐξ οὗ μεταβάλλει καὶ εἰς

ὅν. Πρὸς δὲ τούτοις τί τῆς κινήσεως αἴτιον; Οὐ γὰρ δὴ τό γε

κενόν· οὐ γὰρ αὐτὸ κινεῖται μόνον, ἀλλὰ καὶ τὸ στερεόν.

Ὡσαύτως δὲ συμβαίνει κἄν τις ἄλλως διορίζῃ, μεγέθει καὶ

30 σμικρότητι ποιῶν βαρύτερα καὶ κουφότερα θάτερα τῶν ἑτέρων,

κἂν ἄλλον ὁντινοῦν τρόπον κατασκευάζων, μόνον δὲ τὴν

αὐτὴν ὕλην ἅπασιν ἀποδιδούς, ἢ πλείους μὲν ὑπεναντίας δὲ

μόνον. Μιᾶς μὲν γὰρ οὔσης οὐκ ἔσται τὸ ἁπλῶς βαρὺ καὶ

κοῦφον, ὥσπερ τοῖς ἐκ τῶν τριγώνων συνιστᾶσιν· ἐναντίας δέ,

1But the question is, how will they discriminate the absolutely heavy? Presumably, either by its excess of solid or by its defect of void. On the former view there could be an amount of earth so small as to contain less solid than a large mass of fire. And similarly, if the distinction rests on the amount of 5void, there will be a body, lighter than the absolutely light, which nevertheless moves downward as constantly as the other moves upward. But that cannot be so, since the absolutely light is always lighter than bodies which have weight and move downward, while, on the other hand, that which is lighter need not be light, because in common speech we distinguish a lighter and a heavier (viz. 10water and earth) among bodies endowed with weight. Again, the suggestion of a certain ratio between the void and the solid in a body is no more equal to solving the problem before us. The manner of speaking will issue in a similar impossibility. For any two portions of fire, small or great, will exhibit the same ratio of solid to void, but the upward movement of the greater is quicker than 15that of the less, just as the downward movement of a mass of gold or lead, or of any other body endowed with weight, is quicker in proportion to its size. This, however, should not be the case if the ratio is the ground of distinction between heavy things and light. There is also an absurdity in attributing the upward movement of bodies to a void which does not itself move. If, however, 20it is the nature of a void to move upward and of a plenum to move downward, and therefore each causes a like movement in other things, there was no need to raise the question why composite bodies are some light and some heavy; they had only to explain why these two things are themselves light and heavy respectively, and to give, further, the reason why the plenum and the void are not 25eternally separated. It is also unreasonable to imagine a place for the void, as if the void were not itself a kind of place. But if the void is to move, it must have a place out of which and into which the change carries it. Also what is the cause of its movement? Not, surely, its voidness: for it is not the void only which is moved, but also the solid.
Similar difficulties are involved in 30all other methods of distinction, whether they account for the relative lightness and heaviness of bodies by distinctions of size, or proceed on any other principle, so long as they attribute to each the same matter, or even if they recognize more than one matter, so long as that means only a pair of contraries.

310a

1 καθάπερ οἱ τὸ κενὸν καὶ πλῆρες, οὐκ ἔσται τὰ μεταξὺ τῶν

ἁπλῶς βαρέων καὶ κούφων διὰ τίν' αἰτίαν βαρύτερα καὶ

κουφότερα ἀλλήλων καὶ τῶν ἁπλῶν ἐστιν. Τὸ δὲ μεγέθει καὶ

μικρότητι διορίζειν πεπλασμένῳ μὲν ἔοικε μᾶλλον τῶν πρότερον,

5 ὅτι δ' ἐνδέχεται καθ' ἕκαστον ποιεῖν διαφορὰς τῶν

τεττάρων στοιχείων, ἀσφαλεστέρως ἔχει πρὸς τὰς ἔμπροσθεν

ἀπορίας. Τῷ δὲ μίαν ποιεῖν φύσιν τῶν τῷ μεγέθει διαφερόντων

ἀναγκαῖον ταὐτὸν συμβαίνειν τοῖς μίαν ποιοῦσιν

ὕλην, καὶ μήθ' ἁπλῶς εἶναι μηθὲν κοῦφον μήτε φερόμενον

10 ἄνω, ἀλλ' ἢ ὑστερίζον ἢ ἐκθλιβόμενον, καὶ πολλὰ μικρὰ

ὀλίγων μεγάλων βαρύτερα εἶναι. Εἰ δὲ τοῦτο ἔσται, συμβήσεται

πολὺν ἀέρα καὶ πολὺ πῦρ ὕδατος εἶναι βαρύτερα

καὶ γῆς ὀλίγης. Τοῦτο δ' ἐστὶν ἀδύνατον. Τὰ μὲν οὖν

παρὰ τῶν ἄλλων εἰρημένα ταῦτα, καὶ τοῦτον λέγεται τὸν

15 τρόπον.

1If there is a single matter, as with those who compose things of triangles, nothing can be absolutely heavy or light: and if there is one matter and its contrary-the void, for instance, and the plenum-no reason can be given for the relative lightness and heaviness of the bodies intermediate between the absolutely 5light and heavy when compared either with one another or with these themselves. The view which bases the distinction upon differences of size is more like a mere fiction than those previously mentioned, but, in that it is able to make distinctions between the four elements, it is in a stronger position for meeting the foregoing difficulties. Since, however, it imagines that these bodies which 10differ in size are all made of one substance, it implies, equally with the view that there is but one matter, that there is nothing absolutely light and nothing which moves upward (except as being passed by other things or forced up by them); and since a multitude of small atoms are heavier than a few large ones, it will follow that much air or fire is heavier than a little water or earth, 15which is impossible.

Book 4,Chapter 3 (310a16–311a14)

Ἡμεῖς δὲ λέγωμεν πρῶτον διορίσαντες περὶ οὗ μάλιστα

ἀποροῦσί τινες, διὰ τί τὰ μὲν ἄνω φέρεται τὰ δὲ κάτω τῶν

σωμάτων ἀεὶ κατὰ φύσιν, τὰ δὲ καὶ ἄνω καὶ κάτω, μετὰ

δὲ ταῦτα περὶ βαρέος καὶ κούφου καὶ τῶν συμβαινόντων

20 περὶ αὐτὰ παθημάτων, διὰ τίν' αἰτίαν ἕκαστον γίνεται. Περὶ

μὲν οὖν τοῦ φέρεσθαι εἰς τὸν αὑτοῦ τόπον ἕκαστον ὁμοίως ὑποληπτέον

ὥσπερ καὶ περὶ τὰς ἄλλας γενέσεις καὶ μεταβολάς.

Ἐπεὶ γάρ εἰσι τρεῖς αἱ κινήσεις (ἡ μὲν κατὰ μέγεθος,

ἡ δὲ κατ' εἶδος, ἡ δὲ κατὰ τόπον), ἐν ἑκάστῃ τούτων

25 τὴν μεταβολὴν ὁρῶμεν γινομένην ἐκ τῶν ἐναντίων εἰς τὰ

ἐναντία καὶ τὰ μεταξύ, καὶ οὐκ εἰς τὸ τυχὸν τῷ τυχόντι

μεταβολὴν οὖσαν· ὁμοίως δὲ οὐδὲ κινητικὸν τὸ τυχὸν τοῦ τυχόντος·

ἀλλ' ὥσπερ τὸ ἀλλοιωτὸν καὶ τὸ αὐξητὸν ἕτερον,

οὕτω καὶ τὸ ἀλλοιωτικὸν καὶ τὸ αὐξητικόν. Τὸν αὐτὸν δὴ

30 τρόπον ὑποληπτέον καὶ τὸ κατὰ τόπον κινητικὸν καὶ κινητὸν

οὐ τὸ τυχὸν εἶναι τοῦ τυχόντος. Εἰ οὖν εἰς τὸ ἄνω καὶ

τὸ κάτω κινητικὸν μὲν τὸ βαρυντικὸν καὶ τὸ κουφιστικόν,

κινητὸν δὲ τὸ δυνάμει βαρὺ καὶ κοῦφον, τὸ δ' εἰς τὸν αὑτοῦ

τόπον φέρεσθαι ἕκαστον τὸ εἰς τὸ αὑτοῦ εἶδός ἐστι φέρεσθαι

These, then, are the views which have been advanced by others and the terms in which they state them. We may begin our own statement by settling a question which to some has been the main difficulty-the question why some bodies move always and naturally upward and others downward, while others again move both upward and downward. After that we will inquire into light and 20heavy and of the various phenomena connected with them. The local movement of each body into its own place must be regarded as similar to what happens in connexion with other forms of generation and change. There are, in fact, three kinds of movement, affecting respectively the size, the form, and the place of a thing, and in each it is observable that change proceeds from a contrary to a contrary 25or to something intermediate: it is never the change of any chance subject in any chance direction, nor, similarly, is the relation of the mover to its object fortuitous: the thing altered is different from the thing increased, and precisely the same difference holds between that which produces alteration and that which produces increase. In the same manner it must be thought that produces 30local motion and that which is so moved are not fortuitously related. Now, that which produces upward and downward movement is that which produces weight and lightness, and that which is moved is that which is potentially heavy or light, and the movement of each body to its own place is motion towards its own form.

310b

1 (καὶ ταύτῃ μᾶλλον ἄν τις ὑπολάβοι ὃ ἔλεγον οἱ ἀρχαῖοι,

ὅτι τὸ ὅμοιον φέροιτο πρὸς τὸ ὅμοιον. Τοῦτο γὰρ οὐ

συμβαίνει πάντως· οὐ γὰρ ἐάν τις μεταθῇ τὴν γῆν οὗ νῦν

ἡ σελήνη, οἰσθήσεται τῶν μορίων ἕκαστον πρὸς αὐτήν, ἀλλ'

5 ὅπου περ καὶ νῦν. Ὅλως μὲν οὖν τοῖς ὁμοίοις καὶ ἀδιαφόροις

ὑπὸ τῆς αὐτῆς κινήσεως ἀνάγκη τοῦτο συμβαίνειν, ὥσθ' ὅπου

πέφυκεν ἕν τι φέρεσθαι μόριον, καὶ τὸ πᾶν. Ἐπεὶ δ' ὁ τόπος

ἐστὶ τὸ τοῦ περιέχοντος πέρας, περιέχει δὲ πάντα τὰ

κινούμενα ἄνω καὶ κάτω τό τε ἔσχατον καὶ τὸ μέσον, τοῦτο

10 δὲ τρόπον τινὰ γίγνεται τὸ εἶδος τοῦ περιεχομένου, τὸ εἰς τὸν

αὑτοῦ τόπον φέρεσθαι πρὸς τὸ ὅμοιόν ἐστι φέρεσθαι· τὰ γὰρ

ἐφεξῆς ὅμοιά ἐστιν ἀλλήλοις, οἷον ὕδωρ ἀέρι καὶ ἀὴρ πυρί. Ἀνάπαλιν

δὲ λέγειν τοῖς μέσοις ἔστι, τοῖς δ' ἄκροις οὔ, οἷον

ἀέρα μὲν ὕδατι, ὕδωρ δὲ γῇ· ἀεὶ γὰρ τὸ ἀνώτερον πρὸς τὸ

15 ὑφ' αὑτὸ, ὡς εἶδος πρὸς ὕλην, οὕτως ἔχει πρὸς ἄλληλα),

τὸ δὲ ζητεῖν διὰ τί φέρεται τὸ πῦρ ἄνω καὶ ἡ γῆ κάτω,

τὸ αὐτό ἐστι καὶ διὰ τί τὸ ὑγιαστὸν ἂν κινῆται καὶ μεταβάλλῃ

ᾗ ὑγιαστόν, εἰς ὑγίειαν ἔρχεται ἀλλ' οὐκ εἰς λευκότητα.

Ὁμοίως δὲ καὶ τἆλλα πάντα τὰ ἀλλοιωτά. Ἀλλὰ

20 μὴν καὶ τὸ αὐξητὸν ὅταν μεταβάλλῃ ᾗ αὐξητόν, οὐκ εἰς

ὑγίειαν ἔρχεται ἀλλ' εἰς μεγέθους ὑπεροχήν. Ὁμοίως δὲ καὶ

τούτων ἕκαστον τὸ μὲν ἐν τῷ ποιῷ, τὸ δ' ἐν τῷ ποσῷ μεταβάλλει,

καὶ ἐν τόπῳ τὰ μὲν κοῦφα ἄνω, τὰ δὲ βαρέα

κάτω. Πλὴν ὅτι τὰ μὲν ἐν αὑτοῖς δοκεῖ ἔχειν ἀρχὴν τῆς

25 μεταβολῆς (λέγω δὲ τὸ βαρὺ καὶ τὸ κοῦφον), τὰ δ' οὔ,

ἀλλ' ἔξωθεν, οἷον τὸ ὑγιαστὸν καὶ τὸ αὐξητόν. Καίτοι ἐνίοτε

καὶ ταῦτα ἐξ αὑτῶν μεταβάλλει, καὶ μικρᾶς γενομένης

ἐν τοῖς ἔξω κινήσεως τὸ μὲν εἰς ὑγίειαν ἔρχεται, τὸ δ' εἰς

αὔξην· καὶ ἐπεὶ ταὐτὸν τὸ ὑγιαστὸν καὶ τὸ νόσου δεκτικόν,

30 ἐὰν μὲν κινηθῇ ᾗ ὑγιαστόν, εἰς ὑγίειαν φέρεται, ἐὰν δ' ᾗ

νοσερόν, εἰς νόσον. Μᾶλλον δὲ τὸ βαρὺ καὶ τὸ κοῦφον τούτων

ἐν ἑαυτοῖς ἔχειν φαίνεται τὴν ἀρχὴν διὰ τὸ ἐγγύτατα τῆς

οὐσίας εἶναι τὴν τούτων ὕλην· σημεῖον δ' ὅτι ἡ φορὰ ἀπολελυμένων

ἐστί, καὶ γενέσει ὑστάτη τῶν κινήσεων, ὥστε πρώτη

1(It is best to interpret in this sense the common statement of the older writers that 'like moves to like'. For the words are not in every sense true to fact. If one were to remove the earth to where the moon now is, the various fragments of earth would each move not towards it but to the place in which it now is. In general, 5when a number of similar and undifferentiated bodies are moved with the same motion this result is necessarily produced, viz. that the place which is the natural goal of the movement of each single part is also that of the whole. But since the place of a thing is the boundary of that which contains it, and the continent of all things that move upward or downward is the extremity and the centre, and this 10boundary comes to be, in a sense, the form of that which is contained, it is to its like that a body moves when it moves to its own place. For the successive members of the scries are like one another: water, I mean, is like air and air like fire, and between intermediates the relation may be converted, though not between them and the extremes; thus air is like water, but water is like earth: for the 15relation of each outer body to that which is next within it is that of form to matter.) Thus to ask why fire moves upward and earth downward is the same as to ask why the healable, when moved and changed qua healable, attains health and not whiteness; and similar questions might be asked concerning any other subject of aletion. Of course the subject of increase, when changed qua increasable, attains not 20health but a superior size. The same applies in the other cases. One thing changes in quality, another in quantity: and so in place, a light thing goes upward, a heavy thing downward. The only difference is that in the last case, viz. that of the heavy and the light, the bodies are thought to have a spring of change within themselves, while the subjects of healing and increase are thought to be moved purely 25from without. Sometimes, however, even they change of themselves, ie. in response to a slight external movement reach health or increase, as the case may be. And since the same thing which is healable is also receptive of disease, it depends on whether it is moved qua healable or qua liable to disease whether the motion is towards health or towards disease. But the reason why the heavy and the light 30appear more than these things to contain within themselves the source of their movements is that their matter is nearest to being. This is indicated by the fact that locomotion belongs to bodies only when isolated from other bodies, and is generated last of the several kinds of movement; in order of being then it will be first.

311a

1 ἂν εἴη κατὰ τὴν οὐσίαν αὕτη ἡ κίνησις. Ὅταν μὲν οὖν γίγνηται

ἐξ ὕδατος ἀὴρ καὶ ἐκ βαρέος κοῦφον, ἔρχεται εἰς τὸ ἄνω.

Ἅμα δ' ἐστὶ κοῦφον, καὶ οὐκέτι γίνεται, ἀλλ' ἐκεῖ ἐστιν. Φανερὸν

δὴ ὅτι δυνάμει ὄν, εἰς ἐντελέχειαν ἰὸν ἔρχεται ἐκεῖ

5 καὶ εἰς τὸ τοσοῦτον καὶ τὸ τοιοῦτον, οὗ ἡ ἐντελέχεια καὶ ὅσου

καὶ οἵου [καὶ ὅπου]. Τὸ δ' αὐτὸ αἴτιον καὶ τοῦ ἤδη ὑπάρχοντα

καὶ ὄντα γῆν καὶ πῦρ κινεῖσθαι εἰς τοὺς αὑτῶν τόπους μηδενὸς

ἐμποδίζοντος. Καὶ γὰρ ἡ τροφή, ὅταν τὸ κωλῦον, καὶ τὸ

ὑγιαστόν, ὅταν τὸ ἐπίσχον μὴ ᾖ, φέρεται εὐθύς. Κινεῖ

10 δὲ τό τε ἐξ ἀρχῆς ποιῆσαν καὶ τὸ ὑποσπάσαν ἢ ὅθεν ἀπεπήδησεν,

καθάπερ εἴρηται ἐν τοῖς πρώτοις λόγοις, ἐν οἷς διωρίζομεν

ὅτι οὐθὲν τούτων αὐτὸ ἑαυτὸ κινεῖ. Διὰ τίνα μὲν οὖν

αἰτίαν φέρεται τῶν φερομένων ἕκαστον, καὶ τὸ φέρεσθαι εἰς

τὸν αὑτοῦ τόπον τί ἐστιν, εἴρηται.

1Now whenever air comes into being out of water, light out of heavy, it goes to the upper place. It is forthwith light: becoming is at an end, and in that place it has being. Obviously, then, it is a potentiality, which, in its passage to actuality, comes into that place and quantity and quality which belong 5to its actuality. And the same fact explains why what is already actually fire or earth moves, when nothing obstructs it, towards its own place. For motion is equally immediate in the case of nutriment, when nothing hinders, and in the case of the thing healed, when nothing stays the healing. But the movement is also due to the original creative force and to that which removes 10the hindrance or off which the moving thing rebounded, as was explained in our opening discussions, where we tried to show how none of these things moves itself. The reason of the various motions of the various bodies, and the meaning of the motion of a body to its own place, have now been explained.

Book 4,Chapter 4 (311a15–312a21)

15 Τὰς δὲ διαφορὰς καὶ τὰ συμβαίνοντα περὶ αὐτὰ νῦν

λέγωμεν. Πρῶτον μὲν οὖν διωρίσθω, καθάπερ φαίνεται πᾶσι,

βαρὺ μὲν ἁπλῶς τὸ πᾶσιν ὑφιστάμενον, κοῦφον δὲ τὸ πᾶσιν

ἐπιπολάζον. Ἁπλῶς δὲ λέγω εἴς τε τὸ γένος βλέπων, καὶ

ὅσοις μὴ ἀμφότερα ὑπάρχει· οἷον φαίνεται πυρὸς μὲν τὸ

20 τυχὸν μέγεθος ἄνω φερόμενον, ἐὰν μή τι τύχῃ κωλῦον ἕτερον,

γῆς δὲ κάτω· τὸν αὐτὸν δὲ τρόπον καὶ θᾶττον τὸ πλεῖον.

Ἄλλως δὲ βαρὺ καὶ κοῦφον, οἷς ἀμφότερα ὑπάρχει· καὶ

γὰρ ἐπιπολάζουσί τισι καὶ ὑφίστανται, καθάπερ ἀὴρ καὶ

ὕδωρ· ἁπλῶς μὲν γὰρ οὐδέτερον τούτων κοῦφον ἢ βαρύ· γῆς

25 μὲν γὰρ ἄμφω κουφότερα (ἐπιπολάζει γὰρ αὐτῇ τὸ τυχὸν

αὐτῶν μόριον), πυρὸς δὲ βαρύτερα (ὑφίσταται γὰρ αὐτῶν ὁπόσον

ἂν ᾖ μόριον), πρὸς ἑαυτὰ δὲ ἁπλῶς τὸ μὲν βαρὺ τὸ δὲ

κοῦφον· ἀὴρ μὲν γὰρ ὁπόσος ἂν ᾖ, ἐπιπολάζει ὕδατι, ὕδωρ

δὲ ὁπόσον ἂν ᾖ, ἀέρι ὑφίσταται. Ἐπεὶ δὲ καὶ τῶν ἄλλων τὰ

30 μὲν ἔχει βάρος τὰ δὲ κουφότητα, δῆλον ὅτι τούτων μὲν αἰτία

πάντων ἡ ἐν τοῖς ἀσυνθέτοις διαφορά· κατὰ γὰρ τὸ

ἐκείνων τετυχηκέναι τοῦ μὲν πλεῖον τοῦ δ' ἔλαττον, ἔσται τὰ

μὲν κοῦφα τὰ δὲ βαρέα τῶν σωμάτων. Ὥστε περὶ ἐκείνων

λεκτέον· τἆλλα γὰρ ἀκολουθεῖ τοῖς πρώτοις, ὅπερ ἔφαμεν

35 χρῆναι ποιεῖν καὶ τοὺς διὰ τὸ πλῆρες τὸ βαρὺ λέγοντας

We have now to speak of the distinctive properties of these bodies and of the various 15phenomena connected with them. In accordance with general conviction we may distinguish the absolutely heavy, as that which sinks to the bottom of all things, from the absolutely light, which is that which rises to the surface of all things. I use the term 'absolutely', in view of the generic character of 'light' and 'heavy', in order to confine the application to bodies which do 20not combine lightness and heaviness. It is apparent, I mean, that fire, in whatever quantity, so long as there is no external obstacle moves upward, and earth downward; and, if the quantity is increased, the movement is the same, though swifter. But the heaviness and lightness of bodies which combine these qualities is different from this, since while they rise to the surface of 25some bodies they sink to the bottom of others. Such are air and water. Neither of them is absolutely either light or heavy. Both are lighter than earth-for any portion of either rises to the surface of it-but heavier than fire, since a portion of either, whatever its quantity, sinks to the bottom of fire; compared together, however, the one has absolute weight, the other absolute 30lightness, since air in any quantity rises to the surface of water, while water in any quantity sinks to the bottom of air. Now other bodies are severally light and heavy, and evidently in them the attributes are due to the difference of their uncompounded parts: that is to say, according as the one or the other happens to preponderate the bodies will be heavy and light respectively.

311b

1 καὶ διὰ τὸ κενὸν τὸ κοῦφον. Συμβαίνει δὴ μὴ πανταχοῦ

ταὐτὰ βαρέα δοκεῖν εἶναι καὶ κοῦφα διὰ τὴν τῶν πρώτων διαφοράν·

λέγω δ' οἷον ἐν μὲν ἀέρι βαρύτερον ἔσται ταλαντιαῖον

ξύλον μολίβδου μναϊαίου, ἐν δὲ ὕδατι κουφότερον· αἴτιον δ'

5 ὅτι πάντα βάρος ἔχει πλὴν πυρὸς καὶ κουφότητα πλὴν γῆς.

Γῆν μὲν οὖν καὶ ὅσα γῆς ἔχει πλεῖστον, πανταχοῦ βάρος ἔχειν

ἀναγκαῖον, ὕδωρ δὲ πανταχοῦ πλὴν ἐν γῇ, ἀέρα δὲ πλὴν ἐν

ὕδατι καὶ γῇ· ἐν τῇ αὑτοῦ γὰρ χώρᾳ πάντα βάρος ἔχει

πλὴν πυρός, καὶ ὁ ἀήρ. Σημεῖον δ' ὅτι ἕλκει πλεῖον ὁ πεφυσημένος

10 ἀσκὸς τοῦ κενοῦ. Ὥστ' εἴ τι ἀέρος ἔχει πλεῖον ἢ

γῆς καὶ ὕδατος, ἐν μὲν ὕδατι ἐνδέχεται κουφότερον εἶναί

τινος, ἐν δὲ ἀέρι βαρύτερον· ἀέρι μὲν γὰρ οὐκ ἐπιπολάζει,

τῷ δὲ ὕδατι ἐπιπολάζει. Ὅτι δ' ἐστί τι ἁπλῶς κοῦφον καὶ

ἁπλῶς βαρύ, ἐκ τῶνδ' ἐστὶ φανερόν. Λέγω δ' ἁπλῶς κοῦφον

15 ὃ ἀεὶ ἄνω καὶ βαρὺ ὃ ἀεὶ κάτω πέφυκε φέρεσθαι μὴ

κωλυόμενον· τοιαῦτα γάρ ἐστί τινα, καὶ οὐχ ὥσπερ οἴονταί

τινες πάντ' ἔχειν βάρος· βαρὺ μὲν γὰρ δοκεῖ τισιν εἶναι καὶ

ἑτέροις, καὶ ἀεὶ φέρεσθαι πρὸς τὸ μέσον. Ἔστι δ' ὁμοίως καὶ

τὸ κοῦφον. Ὁρῶμεν γάρ, καθάπερ εἴρηται πρότερον, ὅτι τὰ

20 γεηρὰ πᾶσιν ὑφίσταται καὶ φέρεται πρὸς τὸ μέσον. Ἀλλὰ

μὴν ὥρισται τὸ μέσον. Εἰ τοίνυν ἐστί τι ὃ πᾶσιν ἐπιπολάζει,

καθάπερ φαίνεται τὸ πῦρ καὶ ἐν αὐτῷ τῷ ἀέρι ἄνω φερόμενον,

ὁ δ' ἀὴρ ἡσυχάζων, δῆλον ὅτι τοῦτο φέρεται πρὸς τὸ

ἔσχατον. Ὥστε βάρος οὐδὲν οἷόν τ' ἔχειν αὐτό· ὑφίστατο γὰρ

25 ἂν ἄλλῳ· εἰ δὲ τοῦτο, εἴη ἄν τι ἄλλο, ὃ φέρεται ἐπὶ τὸ

ἔσχατον, ὃ πᾶσι τοῖς φερομένοις ἐπιπολάζει. Νῦν δ' οὐδὲν

φαίνεται. Τὸ ἄρα πῦρ οὐδὲν ἔχει βάρος, οὐδὲ ἡ γῆ κουφότητα

οὐδεμίαν, εἴπερ ὑφίσταται πᾶσι καὶ τὸ ὑφιστάμενον

φέρεται ἐπὶ τὸ μέσον. Ἀλλὰ μὴν ὅτι γ' ἐστὶ μέσον πρὸς ὃ

30 ἡ φορὰ τοῖς ἔχουσι βάρος καὶ ἀφ' οὗ τοῖς κούφοις, δῆλον

πολλαχόθεν. Πρῶτον μὲν τῷ εἰς ἄπειρον μὴ ἐνδέχεσθαι

φέρεσθαι μηθέν. Ὥσπερ γὰρ οὐκ ἔστιν οὐθὲν ἀδύνατον, οὕτως

οὐδὲ γίγνεται· ἡ δὲ φορὰ γένεσίς ποθέν ποι. Ἔπειτα πρὸς

ὁμοίας φαίνεται γωνίας τὸ μὲν πῦρ ἄνω φερόμενον, ἡ δὲ

35 γῆ κάτω καὶ πᾶν τὸ βάρος ἔχον. Ὥστ' ἀνάγκη φέρεσθαι

1Therefore we need only speak of these parts, since they are primary and all else consequential: and in so doing we shall be following the advice which we gave to those whose attribute heaviness to the presence of plenum and lightness to that of void. It is due to the properties of the elementary bodies that a body which is regarded as light in one place 5is regarded as heavy in another, and vice versa. In air, for instance, a talent's weight of wood is heavier than a mina of lead, but in water the wood is the lighter. The reason is that all the elements except fire have weight and all but earth lightness. Earth, then, and bodies in which earth preponderates, must needs have weight everywhere, while water is heavy anywhere but in earth, and air is heavy when not in water or earth. In its 10own place each of these bodies has weight except fire, even air. Of this we have evidence in the fact that a bladder when inflated weighs more than when empty. A body, then, in which air preponderates over earth and water, may well be lighter than something in water and yet heavier than it in air, since such a body does not rise in air but rises to the surface in water.
The following account will make it plain that there is an absolutely 15light and an absolutely heavy body. And by absolutely light I mean one which of its own nature always moves upward, by absolutely heavy one which of its own nature always moves downward, if no obstacle is in the way. There are, I say, these two kinds of body, and it is not the case, as some maintain, that all bodies have weight. Different views are in fact agreed that there is a heavy body, which moves uniformly towards the centre. But is 20also similarly a light body. For we see with our eyes, as we said before, that earthy things sink to the bottom of all things and move towards the centre. But the centre is a fixed point. If therefore there is some body which rises to the surface of all things-and we observe fire to move upward even in air itself, while the air remains at rest-clearly this body is moving towards the extremity. It cannot then have any weight. If it had, 25there would be another body in which it sank: and if that had weight, there would be yet another which moved to the extremity and thus rose to the surface of all moving things. In fact, however, we have no evidence of such a body. Fire, then, has no weight. Neither has earth any lightness, since it sinks to the bottom of all things, and that which sinks moves to the centre. That there is a centre towards which the motion of heavy things, and 30away from which that of light things is directed, is manifest in many ways. First, because no movement can continue to infinity. For what cannot be can no more come-to-be than be, and movement is a coming to-be in one place from another. Secondly, like the upward movement of fire, the downward movement of earth and all heavy things makes equal angles on every side with the earth's surface: it must therefore be directed towards the centre.

312a

1 πρὸς τὸ μέσον. (Τοῦτο δὲ πότερον συμβαίνει πρὸς τὸ τῆς

γῆς μέσον ἢ πρὸς τὸ τοῦ παντός, ἐπεὶ ταὐτὸν αὐτῶν ἐστιν, ἄλλος

λόγος.) Ἐπεὶ δὲ τὸ πᾶσιν ὑφιστάμενον φέρεται πρὸς τὸ μέσον,

ἀνάγκη τὸ πᾶσιν ἐπιπολάζον φέρεσθαι πρὸς τὸ ἔσχατον

5 τῆς χώρας, ἐν ᾗ ποιοῦνται τὴν κίνησιν· ἐναντίον γὰρ τὸ μὲν

μέσον τῷ ἐσχάτῳ, τὸ δὲ ὑφιστάμενον ἀεὶ τῷ ἐπιπολάζοντι.

Διὸ καὶ εὐλόγως τὸ βαρὺ καὶ κοῦφον δύο ἐστίν· καὶ γὰρ οἱ

τόποι δύο, τὸ μέσον καὶ τὸ ἔσχατον. Ἔστι δὲ δή τι καὶ

μεταξὺ τούτων, ὃ πρὸς ἑκάτερον αὐτῶν λέγεται θάτερον·

10 ἔστι γὰρ ὡς ἔσχατον καὶ μέσον ἀμφοτέρων ἐστὶ τὸ μεταξύ·

διὰ τοῦτό ἐστί τι καὶ ἄλλο βαρὺ καὶ κοῦφον, οἷον ὕδωρ καὶ

ἀήρ. Φαμὲν δὲ τὸ μὲν περιέχον τοῦ εἴδους εἶναι, τὸ δὲ περιεχόμενον

τῆς ὕλης. Ἔστι δ' ἐν πᾶσι τοῖς γένεσιν αὕτη ἡ διάστασις·

καὶ γὰρ ἐν τῷ ποιῷ καὶ ἐν τῷ ποσῷ ἐστι τὸ μὲν

15 ὡς εἶδος μᾶλλον, τὸ δ' ὡς ὕλη. Καὶ ἐν τοῖς κατὰ τόπον

ὡσαύτως τὸ μὲν ἄνω τοῦ ὡρισμένου, τὸ δὲ κάτω τῆς ὕλης.

Ὥστε καὶ ἐν αὐτῇ τῇ ὕλῃ τῇ τοῦ βαρέος καὶ κούφου, ᾗ μὲν

τοιοῦτον δυνάμει, βαρέος ὕλη, ᾗ δὲ τοιοῦτον, κούφου· καὶ ἔστι

μὲν ἡ αὐτή, τὸ δ' εἶναι οὐ ταὐτόν, ὥσπερ καὶ τὸ νοσερὸν

20 καὶ τὸ ὑγιαστόν. Τὸ γὰρ εἶναι οὐ ταὐτόν· διόπερ οὐδὲ τὸ νοσώδει

εἶναι ἢ ὑγιεινῷ.

1Whether it is really the centre of the earth and not rather that of the whole to which it moves, may be left to another inquiry, since these are coincident. But since that which sinks to the bottom of all things moves to the centre, necessarily that which rises to the surface moves to the extremity of the region in which the 5movement of these bodies takes place. For the centre is opposed as contrary to the extremity, as that which sinks is opposed to that which rises to the surface. This also gives a reasonable ground for the duality of heavy and light in the spatial duality centre and extremity. Now there is also the intermediate region to which each name is given in opposition to the other extreme. For that which is intermediate 10between the two is in a sense both extremity and centre. For this reason there is another heavy and light; namely, water and air. But in our view the continent pertains to form and the contained to matter: and this distinction is present in every genus. Alike in the sphere of quality and in that of quantity there is that which corresponds rather to form and that which corresponds to matter. In the same way, among 15spatial distinctions, the above belongs to the determinate, the below to matter. The same holds, consequently, also of the matter itself of that which is heavy and light: as potentially possessing the one character, it is matter for the heavy, and as potentially possessing the other, for the light. It is the same matter, but its being is different, as that which is receptive of disease is the same as that which 20is receptive of health, though in being different from it, and therefore diseasedness is different from healthiness.

Book 4,Chapter 5 (312a22–313a15)

Τὸ μὲν οὖν ἔχον τοιαύτην ὕλην κοῦφον καὶ ἀεὶ ἄνω,

τὸ δὲ τὴν ἐναντίαν βαρὺ καὶ ἀεὶ κάτω· τὸ δ' ἑτέρας μὲν

τούτων, ἐχούσας δ' οὕτω πρὸς ἀλλήλας ὡς αὗται ἁπλῶς,

25 καὶ ἄνω καὶ κάτω [φερομένας]· διὸ ἀὴρ καὶ ὕδωρ ἔχουσι

καὶ κουφότητα καὶ βάρος ἑκάτερον, καὶ ὕδωρ μὲν πλὴν

γῆς πᾶσιν ὑφίσταται, ἀὴρ δὲ πλὴν πυρὸς πᾶσιν ἐπιπολάζει.

Ἐπεὶ δ' ἐστὶν ἓν μόνον ὃ πᾶσιν ἐπιπολάζει καὶ ἓν ὃ πᾶσιν

ὑφίσταται, ἀνάγκη δύο ἄλλα εἶναι ἃ καὶ ὑφίσταταί τινι

30 καὶ ἐπιπολάζει τινί. Ὥστε ἀνάγκη καὶ τὰς ὕλας τοσαύτας

εἶναι ὅσαπερ ταῦτα, τέτταρας, οὕτω δὲ τέτταρας ὡς μίαν

μὲν ἁπάντων τὴν κοινήν, ἄλλως τε καὶ εἰ γίγνονται ἐξ ἀλλήλων,

ἀλλὰ τὸ εἶναι ἕτερον. Οὐδὲν γὰρ κωλύει τῶν ἐναντίων

A thing then which has the one kind of matter is light and always moves upward, while a thing which has the opposite matter is heavy and always moves downward. Bodies composed of kinds of matter different from these but having relatively to each other the character which these have absolutely, 25possess both the upward and the downward motion. Hence air and water each have both lightness and weight, and water sinks to the bottom of all things except earth, while air rises to the surface of all things except fire. But since there is one body only which rises to the surface of all things and one only which sinks to the bottom of all things, there must needs be two other bodies which sink in some bodies and 30rise to the surface of others. The kinds of matter, then, must be as numerous as these bodies, i.e. four, but though they are four there must be a common matter of all-particularly if they pass into one another-which in each is in being different.

312b

1 εἶναι μεταξὺ καὶ ἓν καὶ πλείω, ὥσπερ ἐν χρώμασιν·

πολλαχῶς γὰρ λέγεται τὸ μεταξὺ καὶ τὸ μέσον. Ἐν μὲν

οὖν τῇ αὑτοῦ χώρᾳ τῶν ἐχόντων καὶ βάρος καὶ κουφότητα

ἕκαστον ἔχει βάρος (ἡ δὲ γῆ ἐν ἅπασιν)· κουφότητα

5 δ' οὐκ ἔχει, ἀλλ' ἢ ἐν οἷς ἐπιπολάζει. Διὸ καὶ ὑποσπωμένων

μὲν φέρεται εἰς τὰ ἐφεξῆς κάτω, ἀὴρ μὲν εἰς

τὴν τοῦ ὕδατος χώραν, ὕδωρ δὲ εἰς τὴν τῆς γῆς. Ἄνω δ'

εἰς τὴν τοῦ πυρός, ἀναιρουμένου τοῦ πυρός, οὐκ οἰσθήσεται ὁ

ἀήρ, εἰ μὴ βίᾳ, ὥσπερ καὶ τὸ ὕδωρ σπᾶται, ὅταν γένηται

10 τὸ ἐπίπεδον ἓν καὶ θᾶττον σπάσῃ τις ἄνω τῆς φορᾶς,

ἣν φέρεται τὸ ὕδωρ κάτω. Οὐδὲ τὸ ὕδωρ εἰς τὴν τοῦ ἀέρος,

ἀλλ' ἢ ὡς νῦν εἴρηται. Ἡ γῆ δὲ τοῦτο οὐ πάσχει, ὅτι οὐχ

ἓν τὸ ἐπίπεδον. Διὸ τὸ μὲν ὕδωρ εἰς τὸ ἀγγεῖον πυρωθὲν

σπᾶται, γῆ δ' οὔ. Ὥσπερ δὲ οὐδ' ἡ γῆ ἄνω, οὐδὲ τὸ πῦρ

15 κάτω εἶσιν ὑφαιρουμένου τοῦ ἀέρος· οὐδὲν γὰρ ἔχει βάρος

οὐδ' ἐν τῇ αὑτοῦ χώρᾳ, ὥσπερ οὐδ' ἡ γῆ κουφότητα. Φέρεται

δὲ κάτω τὰ δύο ὑποσπωμένων, ὅτι τὸ μὲν ἁπλῶς βαρύ ἐστιν

ὃ πᾶσιν ὑφίσταται, τὸ δὲ πρός τι βαρὺ ὂν εἰς τὴν αὑτοῦ

χώραν ἢ οἷς ἐπιπολάζει, δι' ὁμοιότητα τῆς ὕλης. Ὅτι δ'

20 ἀναγκαῖον ποιεῖν ἴσας τὰς διαφορὰς αὐτοῖς, δῆλον. Εἰ μὲν

γὰρ μία ὕλη πάντων, οἷον ἢ τὸ κενὸν ἢ τὸ πλῆρες ἢ τὸ

μέγεθος ἢ τὰ τρίγωνα, ἢ πάντα ἄνω ἢ πάντα κάτω οἰσθήσεται,

ἡ δὲ ἑτέρα φορὰ οὐκέτι ἔσται· ὥστ' ἢ κοῦφον οὐδὲν

ἔσται ἁπλῶς, εἰ πάντα ῥέπει μᾶλλον τῷ ἐκ μειζόνων εἶναι

25 σωμάτων ἢ ἐκ πλειόνων ἢ ὅτι πλήρη (τοῦτο δὲ ὁρῶμέν τε,

καὶ δέδεικται ὅτι ὁμοίως κάτω τε ἀεὶ καὶ πανταχοῦ φέρεται

καὶ ἄνω)· ἐὰν δὲ τὸ κενὸν ἤ τι τοιοῦτον ὃ ἀεὶ ἄνω, οὐκ

ἔσται ὃ ἀεὶ κάτω. Καὶ τῶν μεταξὺ δὴ ἔνια ἔσται κάτω

θᾶττον γῆς· ἐν γὰρ τῷ πολλῷ ἀέρι τρίγωνα πλείω ἢ τὰ

30 στερεὰ ἢ τὰ μικρὰ ἔσται. Οὐ φαίνεται δ' οὐδὲ ἓν μόριον

ἀέρος κάτω φερόμενον. Ὁμοίως δὲ καὶ ἐπὶ τοῦ κούφου, ἐὰν

ἐκεῖνο ποιῇ τις ὑπερέχειν τῇ ὕλῃ. Ἐὰν δὲ δύο, τὰ μεταξὺ

πῶς ἔσται ποιοῦντα ἃ ποιεῖ ἀήρ τε καὶ ὕδωρ; (Οἷον εἴ τις

1There is no reason why there should not be one or more intermediates between the contraries, as in the case of colour; for 'intermediate' and 'mean' are capable of more than one application.
Now in its own place every body endowed with both weight and lightness has weightwhereas earth has weight everywhere-but they only have lightness 5among bodies to whose surface they rise. Hence when a support is withdrawn such a body moves downward until it reaches the body next below it, air to the place of water and water to that of earth. But if the fire above air is removed, it will not move upward to the place of fire, except by constraint; and in that way water also may be drawn up, when the upward movement of air which has had a common surface with it is 10swift enough to overpower the downward impulse of the water. Nor does water move upward to the place of air, except in the manner just described. Earth is not so affected at all, because a common surface is not possible to it. Hence water is drawn up into the vessel to which fire is applied, but not earth. As earth fails to move upward, so fire fails to move downward when air is withdrawn from beneath it: for fire has 15no weight even in its own place, as earth has no lightness. The other two move downward when the body beneath is withdrawn because, while the absolutely heavy is that which sinks to the bottom of all things, the relatively heavy sinks to its own place or to the surface of the body in which it rises, since it is similar in matter to it.
It is plain that one must suppose as many distinct species of matter as there are 20bodies. For if, first, there is a single matter of all things, as, for instance, the void or the plenum or extension or the triangles, either all things will move upward or all things will move downward, and the second motion will be abolished. And so, either there will be no absolutely light body, if superiority of weight is due to superior size or number of the constituent bodies or to the fullness of the body: but 25the contrary is a matter of observation, and it has been shown that the downward and upward movements are equally constant and universal: or, if the matter in question is the void or something similar, which moves uniformly upward, there will be nothing to move uniformly downward. Further, it will follow that the intermediate bodies move downward in some cases quicker than earth: for air in sufficiently large quantity 30will contain a larger number of triangles or solids or particles. It is, however, manifest that no portion of air whatever moves downward. And the same reasoning applies to lightness, if that is supposed to depend on superiority of quantity of matter.

313a

1 φαίη εἶναι τὸ κενὸν καὶ πλῆρες· τὸ μὲν οὖν πῦρ κενόν,

διὸ ἄνω, τὴν δὲ γῆν πλῆρες, διὸ κάτω· ἀέρα δὲ πλεῖον

πυρὸς ἔχειν, ὕδωρ δὲ γῆς). Ἔσται γάρ τι ὕδωρ ὃ πλεῖον

ἕξει πῦρ ὀλίγου ἀέρος, καὶ ἀὴρ πολὺς ὀλίγου ὕδατος γῆν

5 πλείω, ὥστε δεήσει ἀέρος τι πλῆθος θᾶττον φέρεσθαι κάτω

ὕδατος ὀλίγου. Τοῦτο δ' οὐ φαίνεται οὐδαμοῦ οὐδέποτε. Ἀνάγκη

τοίνυν, ὥσπερ καὶ τὸ πῦρ ἄνω, ὅτι τοδὶ ἔχει, οἷον τὸ κενόν,

τὰ δ' ἄλλα οὔ, καὶ τὴν γῆν κάτω, ὅτι τὸ πλῆρες ἔχει,

καὶ τὸν ἀέρα εἰς τὴν αὑτοῦ καὶ ἀνώτερον τοῦ ὕδατος, ὅτι

10 τοδί τι ἔχει, καὶ τὸ ὕδωρ κάτω, ὅτι τοιόνδε τι. Εἰ δὲ ἦν

ἕν τι ἄμφω ἢ δύο, ἄμφω δ' ὑπάρξει ταῦτα ἑκατέρῳ, ἔσται

τι πλῆθος ἑκατέρου ὃ ὑπερέξει ὕδωρ τε ἀέρος ὀλίγου τῷ

ἄνω καὶ ἀὴρ ὕδατος τῷ κάτω, καθάπερ εἴρηται πολλάκις.

Τὰ δὲ σχήματα οὐκ αἴτια τοῦ φέρεσθαι ἁπλῶς ἢ

15 κάτω ἢ ἄνω, ἀλλὰ τοῦ θᾶττον ἢ βραδύτερον. Δι' ἃς δ' αἰτίας,

1But if, secondly, the kinds of matter are two, it will be difficult to make the intermediate bodies behave as air and water behave. Suppose, for example, that the two asserted are void and plenum. Fire, then, as moving upward, will be void, earth, as moving downward, plenum; and in air, it will be said, fire preponderates, in 5water, earth. There will then be a quantity of water containing more fire than a little air, and a large amount of air will contain more earth than a little water: consequently we shall have to say that air in a certain quantity moves downward more quickly than a little water. But such a thing has never been observed anywhere. Necessarily, then, as fire goes up because it has something, e.g. void, which 10other things do not have, and earth goes downward because it has plenum, so air goes to its own place above water because it has something else, and water goes downward because of some special kind of body. But if the two bodies are one matter, or two matters both present in each, there will be a certain quantity of each at which water will excel a little air in the upward movement and air excel water in 15the downward movement, as we have already often said.

Book 4,Chapter 6 (313a16–313b23)

οὐ χαλεπὸν ἰδεῖν· ἀπορεῖται γὰρ νῦν διὰ τί τὰ πλατέα

σιδήρια καὶ μόλιβδος ἐπιπλεῖ ἐπὶ τοῦ ὕδατος, ἄλλα

δὲ ἐλάττω καὶ ἧττον βαρέα, ἂν ᾖ στρογγύλα ἢ μακρά,

οἷον βελόνη, κάτω φέρεται, καὶ ὅτι ἔνια διὰ μικρότητα

20 ἐπιπλεῖ, οἷον τὸ ψῆγμα καὶ ἄλλα γεώδη καὶ κονιορτώδη

ἐπὶ τοῦ ἀέρος. Περὶ δὴ τούτων ἁπάντων τὸ μὲν νομίζειν αἴτιον

εἶναι ὥσπερ Δημόκριτος οὐκ ὀρθῶς ἔχει. Ἐκεῖνος γάρ

φησι τὰ ἀναφερόμενα θερμὰ ἐκ τοῦ ὕδατος ἀνακωχεύειν

The shape of bodies will not account for their moving upward or downward in general, though it will account for their moving faster or slower. The reasons for this are not difficult to see. For the problem thus raised is why a flat piece of iron or lead floats upon water, while smaller and less heavy things, so long as they are round or long-a needle, for 20instance-sink down; and sometimes a thing floats because it is small, as with gold dust and the various earthy and dusty materials which throng the air. With regard to these questions, it is wrong to accept the explanation offered by Democritus.

313b

1 τὰ πλατέα τῶν ἐχόντων βάρος, τὰ δὲ στενὰ διαπίπτειν·

ὀλίγα γὰρ εἶναι τὰ ἀντικρούοντα αὐτοῖς. Ἔδει δ' ἐν τῷ ἀέρι

ἔτι μᾶλλον τοῦτο ποιεῖν, ὥσπερ ἐνίσταται κἀκεῖνος αὐτός.

Ἀλλ' ἐνστὰς λύει μαλακῶς· φησὶ γὰρ οὐκ εἰς ἓν ὁρμᾶν τὸν

5 σοῦν, λέγων τὸν σοῦν τὴν κίνησιν τῶν ἄνω φερομένων σωμάτων.

Ἐπεὶ δ' ἐστὶ τὰ μὲν εὐδιαίρετα τῶν συνεχῶν τὰ δ' ἧττον,

καὶ διαιρετικὰ δὴ τὸν αὐτὸν τρόπον τὰ μὲν μᾶλλον τὰ δ'

ἧττον, ταύτας εἶναι νομιστέον αἰτίας. Εὐδιαίρετον μὲν οὖν τὸ

εὐόριστον, καὶ μᾶλλον τὸ μᾶλλον· ἀὴρ δὲ μᾶλλον ὕδατος

10 τοιοῦτον, ὕδωρ δὲ γῆς. Καὶ τὸ ἔλαττον δὴ ἐν ἑκάστῳ γένει

εὐδιαιρετώτερον καὶ διασπᾶται ῥᾷον. Τὰ μὲν οὖν ἔχοντα

πλάτος διὰ τὸ πολὺ περιλαμβάνειν ἐπιμένει, διὰ τὸ μὴ

διασπᾶσθαι τὸ πλεῖον ῥᾳδίως· τὰ δ' ἐναντίως ἔχοντα τοῖς

σχήμασι διὰ τὸ ὀλίγον περιλαμβάνειν φέρεται κάτω, διὰ

15 τὸ διαιρεῖν ῥᾳδίως. Καὶ ἐν ἀέρι πολὺ μᾶλλον, ὅσῳ εὐδιαιρετώτερος

ὕδατός ἐστιν. Ἐπεὶ δὲ τό τε βάρος ἔχει τινὰ ἰσχὺν

καθ' ἣν φέρεται κάτω, καὶ τὰ συνεχῆ πρὸς τὸ μὴ διασπᾶσθαι,

ταῦτα δεῖ πρὸς ἄλληλα συμβάλλειν· ἐὰν γὰρ

ὑπερβάλλῃ ἡ ἰσχὺς ἡ τοῦ βάρους τῆς ἐν τῷ συνεχεῖ πρὸς

20 τὴν διάσπασιν καὶ διαίρεσιν, βιάσεται κάτω θᾶττον, ἐὰν δὲ

ἀσθενεστέρα ᾖ, ἐπιπολάσει. Περὶ μὲν οὖν βαρέος καὶ κούφου

καὶ τῶν περὶ αὐτὰ συμβεβηκότων διωρίσθω τοῦτον ἡμῖν τὸν

τρόπον.

1He says that the warm bodies moving up out of the water hold up heavy bodies which are broad, while the narrow ones fall through, because the bodies which offer this resistance are not numerous. But this would be even more likely to happen in air-an objection which he himself raises. His reply to the objection is feeble. In the air, he 5says, the 'drive' (meaning by drive the movement of the upward moving bodies) is not uniform in direction. But since some continua are easily divided and others less easily, and things which produce division differ similarly in the case with which they produce it, the explanation must be found in this fact. It is the easily bounded, in proportion as it is easily bounded, which is easily divided; and air is more so than water, 10water than earth. Further, the smaller the quantity in each kind, the more easily it is divided and disrupted. Thus the reason why broad things keep their place is because they cover so wide a surface and the greater quantity is less easily disrupted. Bodies of the opposite shape sink down because they occupy so little of the surface, which is therefore easily parted. And these considerations apply with far greater force 15to air, since it is so much more easily divided than water. But since there are two factors, the force responsible for the downward motion of the heavy body and the disruption-resisting force of the continuous surface, there must be some ratio between the two. For in proportion as the force applied by the heavy thing towards disruption and division exceeds that which resides in the continuum, the quicker will it force its 20way down; only if the force of the heavy thing is the weaker, will it ride upon the surface.
We have now finished our examination of the heavy and the light and of the phenomena connected with them.
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