Míguez
4. ¿Qué relación existe, pues, entre la luz contigua al ojo y la que se da en él, así como entre la que media con el objeto sensible? Digamos en primer lugar que no tiene necesidad del aire como medio. Y si se dijese que la luz no puede existir sin el aire — sin el aire, que es para ella un medio por accidente — , entonces la luz misma sería un medio, y un medio rigurosamente impasible. Pero no tenemos necesidad absoluta de que el medio sea afectado, y si existe en realidad el medio, no se trata de un medio corpóreo, puesto que la luz no es un cuerpo. Por lo demás, el ojo no necesita para ver de una luz extraña e intermedia, sino tan sólo para ver a distancia.
Dejaremos para más adelante el examen de la primera cuestión, esto es, si puede existir la luz sin el aire. Pasaremos, por tanto, a la segunda. Si suponemos antes de nada que la luz contigua al ojo es algo animado, algo por lo que circula y se extiende el alma, como quiera que se da en el interior del ojo, no hay ya necesidad, en cuanto a la percepción visual, de una luz intermedia, sino que la vista se hace semejante al tacto, y la misma facultad de ver, amparada en la luz exterior, percibe real y verdaderamente sin que el medio resulte afectado. Y así pasa al objeto el movimiento de la visión.
Llegados a este punto conviene que nos preguntemos si la visión debe marchar hacia el objeto por la existencia de un intervalo entre el ojo y el objeto o por el hecho de que en este intervalo exista un cuerpo. Si se trata de esto último, es claro que se verá una vez separado el obstáculo; si se trata de lo primero, hay que suponer que la naturaleza del objeto visible es completamente ociosa e inactiva en el acto de la visión. Pero esto parece imposible, porque el tacto no sólo conoce y toca el objeto vecino, sino que se ve afectado por las diferentes especies de cualidades, que, a su vez, da a conocer al alma. De no existir un obstáculo intermedio, también sentiría a distancia, porque es indudable que sentimos el calor del fuego al mismo tiempo que el aire intermedio y no tenemos que esperar en absoluto a que el aire se caliente. Incluso podría decirse que nuestro cuerpo, por su misma solidez, se calienta antes que el aire. De modo que nos calentamos por medio del aire, pero no gracias a él. Por consiguiente, si hay algo que puede actuar, y algo también que puede sufrir, ¿por qué echar mano de un cuerpo intermedio, sobre el cual el objeto ejerza su poder? Esto equivale, en rigor de verdad, a exigir un obstáculo. Porque, en efecto, cuando la luz del sol llega hasta aquí, no es el aire el que primero la siente y luego nosotros, sino que él y nosotros la sentimos a la vez. Incluso la vemos con frecuencia antes de que esté próxima al ojo e iluminando objetos extraños. La contemplamos, pues, sin que el aire sea afectado para nada, esto es, sin que el medio la experimente, ya que no es llegada todavía esa luz a la que el ojo debe unirse. Difícil resulta también en esta hipótesis explicar cómo se ven los astros y, en general, el fuego durante la noche.
Si suponemos que el alma permanece en sí misma, sirviéndose de la luz como de un bastón para ver de anticiparse al objeto visible, la percepción tendrá que ser considerada como una acción violenta, en orden a la resistencia del objeto y al despliegue de la luz, pues lo sensible, como tal color, deberá resistir fuertemente. Así se explican los contactos, por medio de algo interpuesto. Pero, con todo, el objeto debe haber estado directamente en contacto con nosotros, sin la intervención de ningún cuerpo intermedio; porque el contacto que así tiene lugar sólo nos da un conocimiento último, como por ejemplo el de la memoria y, sobre todo, el del razonamiento. No es éste el caso que ahora se ofrece.
Si suponemos, en fin, que el color hace sufrir en primer lugar a la luz próxima al objeto, para llegar luego gradualmente hasta la vista, la hipótesis se vuelve idéntica a la que admitía que el medio es modificado primeramente por el objeto sensible, lo cual ya se ha considerado como incierto en otra parte.
Bouillet
V. Dans quel rapport la lumière qui émane de l’oeil se trouve-t-elle avec la lumière qui est contiguë à l’œil et s’étend jusqu’à l’objet [§ 2]? — Elle n’a pas besoin de l’air comme milieu, à moins qu’on ne dise qu’il n’y a pas de lumière sans air; alors l’air est un milieu par accident. Quant à la lumière elle-même, c’est un milieu qui n’est pas affecté : car il n’est pas nécessaire qu’il y ait ici une affection, mais seulement un milieu ; par conséquent, si la lumière n’est pas un corps, il n’est pas nécessaire qu’il y ait un corps [pour servir de milieu]. On dira peut-être que la vue n’a pas besoin d’une lumière étrangère ni d’un milieu pour voir simplement, mais qu’elle en a besoin pour voir de loin. Nous examinerons plus tard [§ 6] s’il peut y avoir ou non de la lumière sans air. Considérons maintenant le premier point.
Si l’on suppose que la lumière qui est contiguë à l’oeil 416 devienne animée, que l’âme s’y répande en quelque sorte, s’y unisse comme elle s’unit à la lumière intérieure, il n’est pas besoin d’une lumière intermédiaire pour percevoir l’objet visible. La vue ressemble au tact : elle opère dans la lumière en se transportant en quelque sorte à l’objet, sans que le milieu éprouve d’affection (13). Examinons si c’est parce qu’il y a un intervalle, ou parce qu’il y a un corps dans l’intervalle, que la vue doit se transporter à l’objet. Si c’est parce qu’il y a un corps dans l’intervalle, en enlevant cet obstacle, la vision doit avoir lieu. Si c’est simplement parce qu’il y a un intervalle, il faut supposer que la nature de l’objet visible est inerte et tout à fait inactive. Mais cela est impossible : non seulement le tact annonce et touche l’objet voisin, mais encore, par l’affection qu’il éprouve, il fait connaître les différences de l’objet tangible, et le perçoit même de loin, si rien ne s’y oppose : car nous percevons le feu en même temps que l’air qui nous entoure et avant que cet air ait été échauffé. Un corps solide s’échauffe plus que l’air, par conséquent il reçoit de la chaleur à travers l’air plutôt que par l’intermédiaire de l’air. Si donc l’objet visible a la puissance d’agir, et l’organe celle de pâtir, pourquoi la vue aurait-elle besoin d’un autre milieu [que la lumière], afin d’exercer sa puissance? Ce serait avoir besoin d’un obstacle. Quand la lumière du soleil nous arrive, elle n’éclaire pas l’air avant de nous éclairer nous-mêmes, elle l’éclaire en même temps que nous; avant même qu’elle approche de l’œil, tandis qu’elle est encore ailleurs, il nous arrive de voir, comme si 417 l’air n’était pas affecté ; c’est sans doute parce que le milieu n’a pas éprouvé de modification et que la lumière n’est pas encore venue s’unir à notre vue. Dans cette hypothèse [qui admet que l’air reçoit et transmet une affection] il est difficile d’expliquer pourquoi pendant la nuit nous voyons les astres et en général toute espèce de feu.
Si l’on suppose que l’âme reste en elle-même, mais qu’elle se serve de la lumière [émanée de l’œil], comme d’un bâton, pour atteindre l’objet visible, il faudra, en ce cas, que la perception très vive ait pour cause la résistance éprouvée par la lumière dans sa tension (14), et que la couleur sensible, en tant qu’elle est couleur, ait elle-même la propriété de réfléchir la lumière : de cette manière, le contact s’opérera par un milieu. Mais la lumière s’est auparavant approchée de l’objet sans qu’il y eût un milieu ; de cette manière, le contact opéré ensuite par un milieu produirait la connaissance par une espèce de mémoire et de raisonnement. Or il n’en est pas ainsi. Si l’on suppose enfin que la lumière contiguë à l’objet visible soit affectée et transmette ensuite cette affection de proche en proche jusqu’à la vue , cette hypothèse est au fond la même que celle qui prétend que le milieu doit être modifié préalablement par l’objet visible, hypothèse que nous avons déjà discutée plus haut.
Guthrie
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? 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 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 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.
MacKenna
4. But there is the question of the linked light that must relate the visual organ to its object.
Now, firstly: since the intervening air is not necessary – unless in the purely accidental sense that air may be necessary to light – the light that acts as intermediate in vision will be unmodified: vision depends upon no modification whatever. This one intermediate, light, would seem to be necessary, but, unless light is corporeal, no intervening body is requisite: and we must remember that intervenient and borrowed light is essential not to seeing in general but to distant vision; the question whether light absolutely requires the presence of air we will discuss later. For the present one matter must occupy us:
If, in the act of vision, that linked light becomes ensouled, if the soul or mind permeates it and enters into union with it, as it does in its more inward acts such as understanding – which is what vision really is – then the intervening light is not a necessity: the process of seeing will be like that of touch; the visual faculty of the soul will perceive by the fact of having entered into the light; all that intervenes remains unaffected, serving simply as the field over which the vision ranges.
This brings up the question whether the sight is made active over its field by the sheer presence of a distance spread before it, or by the presence of a body of some kind within that distance.
If by the presence of such a body, then there will be vision though there be no intervenient; if the intervenient is the sole attractive agent, then we are forced to think of the visible object as being a Kind utterly without energy, performing no act. But so inactive a body cannot be: touch tells us that, for it does not merely announce that something is by and is touched: it is acted upon by the object so that it reports distinguishing qualities in it, qualities so effective that even at a distance touch itself would register them but for the accidental that it demands proximity.
We catch the heat of a fire just as soon as the intervening air does; no need to wait for it to be warmed: the denser body, in fact, takes in more warmth than the air has to give; in other words, the air transmits the heat but is not the source of our warmth.
When on the one side, that of the object, there is the power in any degree of an outgoing act, and on the other, that of the sight, the capability of being acted upon, surely the object needs no medium through which to be effective upon what it is fully equipped to affect: this would be needing not a help but a hindrance.
Or, again, consider the Dawn: there is no need that the light first flood the air and then come to us; the event is simultaneous to both: often, in fact, we see [in the distance] when the light is not as yet round our eyes at all but very far off, before, that is, the air has been acted upon: here we have vision without any modified intervenient, vision before the organ has received the light with which it is to be linked.
It is difficult to reconcile with this theory the fact of seeing stars or any fire by night.
If [as by the theory of an intervenient] the percipient mind or soul remains within itself and needs the light only as one might need a stick in the hand to touch something at a distance, then the perception will be a sort of tussle: the light must be conceived as something thrusting, something aimed at a mark, and similarly, the object, considered as an illuminated thing, must be conceived to be resistant; for this is the normal process in the case of contact by the agency of an intervenient.
Besides, even on this explanation, the mind must have previously been in contact with the object in the entire absence of intervenient; only if that has happened could contact through an intervenient bring knowledge, a knowledge by way of memory, and, even more emphatically, by way of reasoned comparison [ending in identification]: but this process of memory and comparison is excluded by the theory of first knowledge through the agency of a medium.
Finally, we may be told that the impinging light is modified by the thing to be seen and so becomes able to present something perceptible before the visual organ; but this simply brings us back to the theory of an intervenient changed midway by the object, an explanation whose difficulties we have already indicated.