1. We undertook to discuss the question whether sight is possible in the absence of any intervening medium, such as air or some other form of what is known as transparent body: this is the time and place.
It has been explained that seeing and all sense-perception can occur only through the medium of some bodily substance, since in the absence of body the soul is utterly absorbed in the Intellectual Sphere. Sense-perception being the gripping not of the Intellectual but of the sensible alone, the soul, if it is to form any relationship of knowledge, or of impression, with objects of sense, must be brought in some kind of contact with them by means of whatever may bridge the gap.
The knowledge, then, is realized by means of bodily organs: through these, which [in the embodied soul] are almost of one growth with it, being at least its continuations, it comes into something like unity with the alien, since this mutual approach brings about a certain degree of identity [which is the basis of knowledge].
Admitting, then, that some contact with an object is necessary for knowing it, the question of a medium falls to the ground in the case of things identified by any form of touch; but in the case of sight- we leave hearing over for the present- we are still in doubt; is there need of some bodily substance between the eye and the illumined object?
No: such an intervening material may be a favouring circumstance, but essentially it adds nothing to seeing power. ! Dense bodies, such as clay, actually prevent sight; the less material the intervening substance is, the more clearly we see; the intervening substance, then, is a hindrance, or, if not that, at least not a help.
It will be objected that vision implies that whatever intervenes between seen and seer must first [and progressively] experience the object and be, as it were, shaped to it; we will be reminded that [vision is not a direct and single relation between agent and object, but is the perception of something radiated since] anyone facing to the object from the side opposite to ourselves sees it equally; we will be asked to deduce that if all the space intervening between seen and seer did not carry the impression of the object we could not receive it.
But all the need is met when the impression reaches that which is adapted to receive it; there is no need for the intervening space to be impressed. If it is, the impression will be of quite another order: the rod between the fisher's hand and the torpedo fish is not affected in the same way as the hand that feels the shock. And yet there too, if rod and line did not intervene, the hand would not be affected- though even that may be questioned, since after all the fisherman, we are told, is numbed if the torpedo merely lies in his net.
The whole matter seems to bring us back to that sympathy of which we have treated. If a certain thing is of a nature to be sympathetically affected by another in virtue of some similitude between them, then anything intervening, not sharing in that similitude, will not be affected, or at least not similarly. If this be so, anything naturally disposed to be affected will take the impression more vividly in the absence of intervening substance, even of some substance capable, itself, of being affected.