Necessity of a this is the nous. De mocritus § 46. The diaphanous (described §§ 34-5 supra) is the medium of objective medium of vision. As in the cases of smelling vision: and hearing, so in that of seeing, there is an extraorganic actualized medium, intervening between the organ and the object1. diapha- Without such medium the object could not produce its characteristic effect upon the organ, or the latter be excited from its potentiality to its realization as an organ. Thus if the coloured object be placed directly and immediately on the surface of the eye it cannot be seen. In order, vacuum. therefore, to be affected at all by the colour, the eye requires a medium. This medium is light, or the actualized varieties of diaphanous. The object must excite a movement (not, the diaphanous, both however, a local movement) in the diaphanous medium, wrong in thinking that we could see best in a Air and water, as mediate colour vision. Need of internal whether air or water (for either of these may be media of vision), and this movement must communicate itself somehow to the eye. This medium being absolutely medium- required if we are to see at all, it was a mistake for diaphanous within the Democritus to think that if there were a vacuum (neither eye itself. air nor water) between the eye and its object one would Hence eye water.' The 'consists of see with the maximum of accuracy: 'that we could see even an ant in the sky. The contrary is the fact: medium of without the medium one could see nothing. Air and is itself water are both media of colour. Through them we see colourless. because-in virtue of the diaphanousness common to both all colours though it were a κίνησις, it is still not the particular form of κίνησις called popá, which involves local movement, but an åλλolwois or qualitative change, which he thinks can take place simultaneously in all parts of the diaphanous medium. 1 438 3 ἀλλ ̓ εἴτε φῶς εἴτε ἀήρ ἐστι τὸ μεταξὺ τοῦ ὁρωμένου καὶ τοῦ ὄμματος, ἡ διὰ τούτου κίνησίς ἐστιν ἡ ποιοῦσα τὸ ὁρᾶν. 2 419 12 ἐὰν γάρ τις θῇ τὸ ἔχον χρῶμα ἐπ ̓ αὐτὴν τὴν ὄψιν οὐκ ὄψεται. 3 419 15 ὁρᾶσθαι ἂν ἀκριβῶς καὶ εἰ μύρμηξ ἐν τῷ οὐρανῷ εἴη. 4 Only for the medium of vision has Aristotle a distinctive name— Tò diapavés. He does not name the media of sound and odour, though media are equally necessary for those senses. By later writers they were called (on the analogy of τὸ διαφανές) τὸ διηχές and τὸ δίοσμον respectively. It is remarkable that Aristotle (de Sens. vi. 446a 20–b 27) is quite ready to admit respecting these media, what he denies so stoutly of rò diapavés, that in them the stimulus of sense travels locally and takes time to come from object to organ. th stimulation (kívnois) produced by colour is conveyed through them to the organ of vision, which is thus on its part stimulated to activity. The medium of colour is the same as that of light, sc. the diapavés. This belongs to both water and air, not qua water or air, but qua partaking in common of the nature of the celestial element, or αιθήρι Fire and this αιθήρ, οἱ τὸ ἄνω σῶμα, stimulate the potential diaphanous and render it actual; colour stimulates the actual diaphanous and so becomes visible. But this diaphanous is also a subjective medium of vision. It exists not only outside, but also inside the eye3. It remains to be noticed that that which is to be a fitting medium of all possible colours must itself be colourless. This rule has its analogue in the cases of all the other senses. The medium of sound-air-must be actually soundless; that of odour, inodorous; that of taste, tasteless. So water is tasteless per se. of sight: its nature parts. The § 47. The organ and function of vision. Like all other The organ organs, the eye is defined by its function. All organs are true to their definition only while capable of discharging their and meaning: its functions; e. g. the eye, only as long as it can see. A dead structure, person's eye is no longer an eye in the true sense, but only and various in an ambiguous sense, of the word. The eye is particular organ affected by the stimulation (kívŋois) up by colour in, and propagated through, the diaphanous tial part of medium: affected, i. e. in such a way as to have the sensation of colour. But the kwńoes thus set up in the the pupil : eye must be in some way conveyed to 'the soul'. the function of the 'pupil,' set the essen The diaphanous medium, therefore, which operates 1 οὐ γὰρ ἡ ὕδωρ οὐδ' ᾗ ἀήρ, διαφανές, ἀλλ ̓ ὅτι ἐστί τις φύσις ὑπάρχουσα ἡ αὐτὴ ἐν τούτοις ἀμφοτέροις καὶ ἐν τῷ ἀϊδίῳ τῷ ἄνω σώματι, 4185 7. " And also visible so far as light is its colour. * So, as we shall see (p. 114), the ear has within it a cell of air which is a means of continuing inwards the external medium of sound. * Meteor. iv. 12. 390a 10 seqq.; de An. ii. 1. 412b 20 ǹ õyıs' avrŋ yàp οὐσία ὀφθαλμοῦ ἡ κατὰ τὸν λόγον ἧς ἀπολειπούσης οὐκ ἔστιν ὀφθαλμὸς πλὴν ὁμωνύμως, καθάπερ ὁ λίθινος. For the question whether or how far the sensations realize themselves in the separate organs without stimulating the faculty of central sense, see the chapter on the Sensus Communis, § 48. the eye. Covering of 'Hardeyed' animals. objectively or externally, is also employed on the subjec ive side within the eye itself, for the purpose of transmitting inwards the Kivýσels received by this organ from without. The eye as a living functioning whole1 is named oplaλμós and sometimes oupa. It is an organ, consisting of heterogeneous parts2. But the part of this whole which is properly concerned in vision-that & Bλéme-is the part generally named Kópη, which we usually render the pufil (vide supra § 2, p. 9 n.), but by which, at least from the time of Empedocles forward, the Greek psychologists meant 'ne 'crystalline lens.' Round this internal moist part called Kópη comes what Aristotle calls rò μéλav, probably the iris; and outside of this again is the white. The pupil and vision are to the eye what body and soul respectively are in the economy of the (@ov as a whole. The Kópη is the material part most intimately concerned in seeing. Therefore, for its protection, it is covered with a membrane so thin and clear as not to obstruct vision, and has in higher animals a further protection afforded by the eyelids. The need of this precautionary protection arises from the humid constitution of this visual part. There are creatures whose eyes are even better protected, viz. by scales, but these suffer for it in having less acute vision'. The primary organ of touching, in relation to the flesh as medium, is compared with the pupil (as the primary organ of vision) in relation to the whole diaphanous. If the external medium of vision were organically attached to the pupil, both would form one whole, comparable to that formed of the organ of touch proper and the organically connected environment of flesh which is its medium. 1 413 2 seqq. ἡ κόρη καὶ ἡ ὄψις. μópιov ȧvoμoloμeрés. Cf. 647a 4 seqq. For its anatomical structure according to Aristotle, see Philippson, vλn dvoponím, pp. 230 seqq. 8 491 20 τὸ δ' ἐντὸς τοῦ ὀφθαλμοῦ τὸ μὲν ὑγρὸν ᾧ βλέπει, κόρη, τὸ δὲ περὶ τοῦτο, μέλαν, τὸ δ ̓ ἐκτὸς τούτου, λευκόν. 4 Cf. 413 2: add 1080 11 ὡς ὄψις ἐν ὀφθαλμῷ, νοῦς ἐν ψυχῇ. 5 De Part. An. ii. 13, 657 30 seqq. • 657 34 τὰ σκληρόφθαλμα. 7 421a 13, 657b 36. 8 De Part. An. ii. 8. 653b 23 seqq. § 48. For perfect vision (i. e. both far-sight and clear- Structural sight) there must be a due proportion of moisture in conditions of perfect the eye. Those that have too little are the creatures vision. with gleaming (yλavκá) eyes: those that have too much are the black-eyed (ueλavóμμara). .......... The former see well by night but badly by day, owing to the eye, from its defective amount of vypóv, being over-stimulated in daylight. The latter see well by day but badly by night, because of the small proportion of the fire to the water in the eye, and the weakness of the light in the air at night1. Besides this the membrane which covers the pupil should be transparent, white, and of even superficies. It must be thin, in order that the stimulating process from without may pass straight through it. It must be even, that it may not cast shadows, as it would if wrinkled. One reason why old persons do not see keenly is that the membrane covering the pupil of their eyes, like the whole epidermis, becomes wrinkled and thick with age. This membrane again must be white; for if black it would not be diaphanous. The very essence of black is non-diaphanousness lanterns would not show light if their sides were black. The moisture in the eye, moreover, must be pure (Kabaρóv) and 'symmetrical' with the movement of stimulation. If this is not so, and if the dépua or membrane be not as described above, the eye will not be clear-sighted, i.e. distinguish accurately between visible objects, but may be long-sighted. Creatures with protruding eyes are shortsighted; those with deep-set eyes are long-sighted, the sockets serving as a tube to combine and direct the movement of the visual ray. This explanation holds good whether the ray proceeds outwards, from the eye, or inwards, from the object. constitu § 49. The physical constitution of the visual organ Physical proper interested Aristotle as well as his predecessors. tion of the Empedocles and Plato had followed Alcmaeon (§ 4 supra) visual 1 Cf. 779b 34 seqq., 780a 25 seqq. 2780b 22. In this requirement of ovμuerpia between the kivŋois and vypóv we are reminded of Empedocles. organ proper. Demo critus' attitude. The 'image' reflected in the pupil not the essential factor of vision, as Demo critus and others It is a merely external thing: a phenomenon of reflexion. The eye does not consist of fire. True explana tion of the 'intraocular flash': a phenomenon of in holding that it consists essentially of fire. Aristotle1 preferred to hold with Democritus that it consists of water. Democritus, indeed, came to this conclusion on false grounds. He thought that the eye consists of water because he supposed vision to be merely the mirroring († čμpaois) of external objects in the eye, which consisting of water acts as a mirror. The mirroring which does take place is, however, merely due to the smoothness (eórns) of the surface of the eye; and, as a fact, does not find its full explanation merely in the reflecting surface of the eye in which the image is seen, but requires account to be also taken of the spectator's eye which alone sees this image. In short this is only a case of the reflexion of light3, a subject but imperfectly understood by Democritus and his contemporaries. Democritus, too, should have asked himself why, if vision were merely reflexion, the other surfaces which reflect images do not see as well as the eye. The visive part of the eye is, therefore, of water, but vision takes place not by mirroring in this water, but by the diaphanousness of the latter-a property which it possesses in common with the air and water of the external world. As for the theory that the eye consists of fire, Aristotle reflexion. not only regards it as false, but considers himself to have traced the error to its source. This error is due, he says, to the well-known but misunderstood fact that if the eyeball be suddenly moved or pressed when the eye is closed, or when there is darkness, a flash ('phosphene ') as it were of fire or light is seen within the eye. If this (from which some conclude that the eye consists of fire) gave a real ground for the popular conclusion, and if vision were due 1 De An. iii. 1, 425 4; de Sens. ii, 438a 5 seqq. 2 Among the many signs of spuriousness in the Problems we find that in 960 32 the visual part of the eye is said to be of fire, n pèv ὄψις πυρός. ávákλaois, which sometimes means refraction, e.g. 373b 10 seqq. 438 9, 370 16 οὗτοι μὲν οὖν οὔπω συνήθεις ἦσαν ταῖς περὶ τὴς ἀνακλά σews dócais. For Aristotle's account of it and its relationship to vision and colour see § 40 supra. Democritus (as we have said) would have replied that the soul which sees belongs to the whole organism, not to the eye alone. |