Part 18

1. Above[161] we suggested the question whether it be possible to see without some medium such as the air or a diaphanous body[162]; we shall now try to consider it. It has already been asserted that in general the soul cannot see or feel without the intermediation of some body; for, when completely separated from the body (the soul dwells in the intelligible world). But, as touch consists of perception, not indeed of intelligible entities, but only of sense-objects, the soul cannot see or feel without the intermediation of some body; for when completely separated from some body, the soul dwells in the intelligible world. But, as touch consists of perception, not indeed of intelligible entities, but only of sense-object, the soul in order to come in contact with these sense-objects, must enter into cognitive or affective relation with them by the means of intermediaries which must possess an analogous nature; and that is why the knowledge of bodies must be acquired by the means of corporeal organs. Through these organs which are so interrelated as to form a sort of unity, the soul approaches sense-objects in a manner such as to establish effective communion. That contact between the organ and the cognized object must be established is evident enough for tangible objects, but is doubtful for visible objects. Whether contact be necessary for hearing is a question we shall have to discuss later.[163] Here we shall first discuss whether sight demand a medium between the eye and color.

REFUTATION OF ARISTOTLE'S INSISTENCE ON A MEDIUM OF SIGHT.

If a medium of sight exist, it exists only by accident, and in no way contributes to sight.[164] Since opaque and earthy bodies hinder sight, and as we see so much the better as the medium is more subtle, it may be said, indeed, that mediums contribute to sight, or at least, if they do not contribute such thereto, they may be hindrances as slight (as possible); but evidently a medium, however refined, is some sort of an obstacle, however slight.

THOUGH THE MEDIUM EXPERIENCE AFFECTION, THE ORGANS FEEL IT BETTER WITHOUT THE MEDIUM.

(There is an opinion that) the medium first receives and then transmits the affection, and impression. For instance, if some one stand in front of us, and directs his gaze at some color, he also sees it; but the color would not reach us unless the medium had experienced the affection. To this it may be answered that there is no necessity for the affections to be experienced by the medium, inasmuch as the affection is already experienced by the eye, whose function consists precisely in being affected by color; or at least, if the medium be affected, its affection differs from that of the eye. For instance, a reed interposed between the hand and the fish called the "torpedo," or "electric ray," does not feel the same numbness which it nevertheless communicates to the holding hand; still, the hand would not be affected with numbness unless the reed formed a communication between the fish and the hand.[165] However, the matter is not beyond discussion, for (even without any intermediary, if for instance) the fisher were in (direct contact) with the "ray" inside of the net, he would also feel the electric numbness. This communication therefore seems based on sympathetic affections. That, by virtue of its nature, one being can be sympathetically affected by some other being, does not necessarily imply that the medium, if different, shares that affection; at least (it is certain that) it is not affected in the same manner. In such a case, the organ destined to experience the affection experiences it far better when there is no medium, even when the medium itself is susceptible to some affection.

NECESSITY OF A MEDIUM IN THE THEORIES OF VARIOUS PHILOSOPHERS.

2. If vision[166] presupposes the union of the "light of the eye,"[167] with the light interposed (between the eye) and the sense-object itself, the interposed medium is the light, and this medium is necessary, on this hypothesis. (On the theory of Aristotle) the colored substance produces a modification in the medium; but nothing here would hinder this modification from reaching the eye itself, even when there is no medium. For, in this case, the medium is necessarily modified before the eye is. (The Platonic philosophers) teach that vision operates by an effusion of the light of the eye. They have no need to postulate a medium, unless indeed they should fear that the ray of the eye should lose its way; but this ray is luminous, and the light travels in a straight line. (The Stoics) explain vision by the resistance experienced by the visual ray. They cannot do without a medium.[168] (The Atomists and) the believers in "images" (such as Epicurus), insist that these images move in emptiness, thereby implying the existence of a free space to avoid hindering the images. Consequently as they will be hindered in a direct ratio to the existence of a medium, this opinion does not run counter to our own hypothesis (that there is no medium).

A COSMOLOGICAL MEDIUM IS NECESSARY, BUT IT AFFECTS SIGHT ONLY ACCIDENTALLY.

Those who (with Plotinos himself) teach that vision operates by sympathy, assert that vision is poorer through a medium, because this medium hinders, fetters, and weakens sympathy. In this case, indeed, the medium necessarily weakens sympathy even though it shared the same nature (as the eye and the object), and was affected in the same manner. (It acts like the integument) of some body that is deeply burned by fire applied to it; the interior parts are less affected because they are protected by the exterior parts. There is no doubt that the parts of one and the same animal will be less affected in experiencing sympathy because of the existence of a medium. The affection will be weakened according to the nature of the medium, because such a medium would hinder excess of affection, unless indeed that which is transmitted (by one part to another) is not such as to fail to affect the medium. But if the universe sympathize with itself because it constitutes a single organism, and if we are affected because we are contained within this single organism, and form part of it, why should any continuity be necessary for us to feel a distant object? The single organism, indeed, could not be continuous without the continuity of some medium; this continuous medium is affected only by accident; but otherwise we would have to admit that all can be affected by all. But if these two objects are affected in one manner, and other two objects are affected in another manner, there might not always be need of a medium. Whoever asserts the need of a medium for vision will have to advance a very good argument, inasmuch as that which traverses the air does not always affect the air, and often limits itself to dividing the air. Thus when a stone falls the only thing that happens to the air is that it fails to support the stone. As falling is part of the stone's nature, it would be unreasonable to assert that its falling was due to the reaction exerted by the ambient air. Otherwise we would have to assert that it is this same reaction of the ambient air that makes fire ascend, which is absurd; because the fire, by the rapidity of its motion, forestalls this reaction. That, by the very rapidity of the motion, reaction is accelerated, takes place only by accident, and has no relation to the upward impulsion; for trees grow from above without receiving any (upward) impulsion. Even we, when walking, divide the air without being pushed by the reaction of the air; the air behind us limits itself to filling the void we have created. If then the air allow itself to be divided by bodies without being affected by them, what would hinder the air from permitting free transit for the images to reach the eye, without being thereby divided?

IMAGES DO NOT REACH US BY EFFLUENCE.

If these images do not reach us by some sort of effluence, why should the air be affected, and why should we ourselves be affected only as a result of the affection experienced by the air? If we felt only because the air had been affected before us, we would attribute the sensation of sight not to the visible object, but to the air located near us, as occurs with heat. In the latter case it is not the distant fire, but the air located near us which, being heated, then warms us; for the sensation of heat presupposes contact, which does not occur with vision. We see, not because the sense-object is imposed on the eye (but because the medium is illuminated); now it is necessary for the medium to be illuminated because the air by itself is dark. If the air were not dark, it would have no need of light; for (to effectuate vision) the obscurity, which forms an obstacle to vision, must be overcome by light. That is perhaps the reason why an object placed very near the eye is not seen; for it brings with it the darkness of the air, together with its own.

USELESSNESS OF AIR AS TRANSMITTING MEDIUM PROVED FROM SIGHT OF OBJECTS AT NIGHT.

3. A strong proof that the forms of sense-objects are not seen merely because the air, on being affected, transmits them by relays from point to point, is that even in darkness the fire, the stars, and their forms may be seen. In this case no one would claim that the forms of the objects, being impressed on the obscure air, are transmitted to the eye; otherwise, there would be no obscurity, as the fire, while transmitting its form, would illuminate. Indeed, in the profound obscurity in which the light of the stars is not seen, the fire of signals and of light-houses may be perceived. Should any one, in opposition to the testimony of his senses, claim that even in this case the fire penetrates the air, he should be answered by having it pointed out to him that in that case human vision should distinguish the smallest objects which are in the air, instead of being limited to the perception of the fire. If then we see what is beyond a dark medium, it would be much better seen without any medium whatever.

ABSENCE OF MEDIUM WOULD INTERFERE WITH VISION ONLY BY DESTROYING SYMPATHY.

It might indeed be objected that without medium, vision ceases. This occurs not because of the lack of medium, but because the sympathy of the (universal) organism is in such a case destroyed since a medium presupposes that all the parts of this organism together form but a single being. It would indeed seem to be a general condition necessary for sensation that the universal organism be sympathetic with itself; otherwise, no one thing could participate in the power of any other thing that might happen to be very distant.

VISION IS NOT DEPENDENT ON THE AFFECTION OF THE MEDIUM.

Here is another important (related) question. If there existed another world and organism which had no relation with our world, and if on the surface of the sky was an eye that was looking, would it perceive this other world at a moderate distance, or would it have no relation thereto? This question will be considered later.[169] Now however we shall give a further proof that the medium has nothing to do with vision. If the air were affected, it would experience a material affection, similar to the figure impressed on wax. In this case, a certain part of the object would be impressed on a certain part of the air; and consequently, the part of the air nearest to the eye would receive a part of the visible object, and this part would be of a size equal to that of the pupil. Now a visible object is seen in its entirety, and all those who are in the air equally see it, whether they behold it from the front, or side, or whether they be one behind the other, without however forming mutual obstacles. This proves that every part of the air contains the entire visible object. This cannot be explained by any corporeal affection, but by higher laws, suitable to the soul, and to the (universal) organism which everywhere responds to itself.

MUTUAL RELATION OF THE EYE'S LIGHT AND THE OBJECTIVE LIGHT.

4. What is the mutual relation between the light that emanates from the eye, and the light which is exterior to the eye, and which extends between the eye and the object?[170] Light has no need of air as a medium, unless indeed somebody should undertake to say that there is no light without air, in which case air would be a medium only accidentally. Light itself, however, is an unaffected medium, for there is no necessity here for an affection, but only for a medium; consequently, if light be not a body, there is no need of a body (to act as medium). It might be objected that sight has no need either of a foreign light nor of a medium to see near by, but has need of them for vision at a distance. Later[171] we shall consider whether or not light without air be possible. Now let us consider the first point.

INTERMEDIARY LIGHT IS UNNECESSARY, PARTLY BEING AN OBSTACLE.

If the light which is contiguous to the eye should become animated, and if the soul should, so to speak, interpenetrate it, uniting with it as she unites with the interior light, there would be no need of intermediary light for the perception of the visible object. Sight resembles touch; it operates in light by somehow transferring itself to the object, without the medium experiencing any affection. Now consider: does the sight transfer itself to the visible object because of the existence of an interval between them, or because of the existence of some body in the interval? In the latter case, vision would occur by removing this obstacle. If, on the other hand, it be because of the existence of a mere interval, then the nature of the visible object must seem inert and entirely inactive. This is however impossible; not only does touch announce and experience the neighboring object but, by the affection it experiences, it proclaims the differences of the tangible object, and even perceives it from a distance, if nothing oppose it; for we perceive the fire at the same time as the air that surrounds us, and before this air has been heated by the fire. A solid body heats better than does the air; and consequently it receives heat through the air, rather than by the intermediation of air. If then the visible object have the power to act, and if the organ have the power of experiencing (or suffering), why should sight need any intermediary (besides light) to exert its power? This would really be needing an obstacle! When the light of the sun reaches us, it does not light up the air before lighting us, but lights both simultaneously; even before it has reached the eye, while it is still elsewhere, we have already seen, just as if the air was not affected at all; that is the case, probably, because the medium has undergone no modification, and because light has not yet presented itself to our view. Under this hypothesis (which asserts that the air receives and transmits an affection) it would be difficult to explain why during the night we see the stars and, in general, any kind of fire.

NOT EVEN THE LIGHT OF THE EYE IS TO BE CONSIDERED AS MEDIUM.

On the hypothesis that the soul remains within herself, while making use of the light (emanated from the eye) as a rod to reach the visible object, a very sharp perception would be caused by the resistance experienced by the light in its tension[172] and sense-color. In so far as it is color, the light itself would possess the property of reflecting light. In this case, the contact would take place by a medium. But already before this the light has reached the object without any medium; so that the later contact operated by a medium would produce cognition by a sort of memory or reasoning--which is not the case.

THE OBJECTIVE LIGHT DOES NOT TRANSMIT THE IMAGE BY RELAYS.

The hypothesis that the light contiguous to the visible object is affected, and transmits this affection by relays from point to point into the eye, is essentially identical with that theory which supposes that the medium must be preliminarily modified by the visible object; a hypothesis that has already been discussed above.

NEITHER FOR HEARING IS THE AIR NECESSARY AS A MEDIUM.

5. As to hearing, there are several theories. One is that the air is first set in motion, and that this motion, being transmitted unaltered from point to point from the (location of the) sound-producing air as far as the ear, causes the sound to arrive to the sense. Again, another theory is that the medium is here affected accidentally, and only because it happens to be interposed; so that, if the medium were annihilated, we would feel the sound immediately on its production by the shock of two bodies. We might think that the air must first be set in motion, but the medium interposed (between the first moved air and the ear) plays a different part. The air here seems to be the sovereign condition of the production of sound; for, at the origin of the sound, the shock of two bodies would produce no sound if the air, compressed and struck by their rapid concussion did not transmit the motion from point to point as far as the ear.[173] But if the production of the sound depend on the impulsion impressed on the air, the (qualitative) difference between voices and (instrumental) sounds will challenge explanation; for there is great difference (of "timbre") between metal struck by metal of the same kind, or another. These differences are not merely quantitative, and cannot be attributed to the air which (everywhere) is the same, nor to the force of the stimulus (which may be equal in intensity). Another theory (of Aristotle's) is that the production of voices and sound is due to the air, because the impulsion impressed on the air is sonorous. (To this it should be answered that) air, in so far as it is air, is not the cause of sound; for it resounds only in so far as it resembles some solid body, remaining in its situation, before it dilates, as if it were something solid.[174] The (cause of the sound) then is the shock between objects, which forms the sound that reaches the sense of hearing. This is demonstrated by the sounds produced in the interior of animals, without the presence of any air, whenever one part is struck by some other. Such is the sound produced by certain articulations when they are bent (as, the knee); or certain bones, when they are struck against each other, or when they break; in this case air has nothing to do with the production of the sound. These considerations compel a theory of hearing similar to our conclusions about sight. The perception of audition, like that of vision, therefore consists in a repercussion (an affection sympathetically felt) in the universal organism.

THE RELATION OF THE AIR TO THE LIGHT.

6. Could light exist without air, if the sun illuminated the surface of bodies, and if there were a void in the interval which is accidentally illuminated by virtue of its location (between the sun and the bodies)? It is certain that if the other things were affected because the air itself was affected, and if light were nothing more than an affection of the air, that is, its substance; then indeed this affection could not exist without the experiencing subject (the air). But (in our view) light is not essentially characteristic of air as such; for all fiery and brilliant bodies, among which are precious stones, possess a luminous color. Could that which passes from a brilliant body into some other body exist without that other body? If light be but a simple quality of an object, and as every quality implies a subject on which it depends, light will have to be sought in the body in which it resides. If, on the contrary, light be only an actualization produced by some other thing, and if there be no body contiguous to the luminous object, and it be entirely surrounded by a void, why could light not exist, and radiate upwards (as well as downwards, and in every direction)? Since light radiates, why should it not radiate without hindrance? If its nature be to fall, it will spontaneously descend; for neither the air nor any illuminated body will make it issue from the illuminating body, nor can force it to advance, since it is neither an accident that implies a subject, nor an affection that implies an affected object. Otherwise, the light would remain (in the illuminated body) when the object from which it emanates should happen to withdraw; but since the light withdraws with it, it radiates. In what direction does light radiate? (Its radiation) demands no more than the existence of sufficient space; otherwise the body of the sun would lose its actualization; that is, the light it radiates. In this case light would not be the quality of a subject, but the actualization that emanates from a subject, but which does not pass into any other subject (as a kind of undulation); but if another subject be present, it will suffer an affection. As life, which constitutes an actualization of the soul, affects the body if it be present, and does not any the less constitute an actualization if the body be absent, likewise light constitutes an actualization subject to the same conditions. It is not the obscurity of the air that begets light, nor obscurity mingled with the earth which produces an impure light; otherwise one might produce something sweet by mingling some thing with what is bitter. The statement that light is a modification of the air, is incomplete without the addition that the air must itself be modified by this modification, and that the obscurity of the air is no longer obscure after having undergone that change. The air itself, however, remains what it was, just as if it had not been affected. The affection belongs only to that which has been affected. Color therefore does not belong to the air, but subsists in itself; the air's only function is its presence. But enough of this.

DOES THE WITHDRAWAL OF THE LUMINOUS SOURCE ABANDON THE LIGHT TO DESTRUCTION; OR DOES THE LIGHT FOLLOW IT?