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.