f? If the metaphysician should say, that he refers to an eye
of the latter description, then the plain man's answer should be--that he
has no experience of any such eye--that he cannot conceive it--that he
knows nothing at all about it--and that the only eye which he ever thinks
or speaks of, is the eye appertaining to, and situated within, the
phenomenon which he calls his visible body. Is _this_, then, the eye which
the metaphysician refers to, and which he tells us we never get beyond? If
it be--why, then, the very admission that this eye is a part of the
visible body, (and what else can we conceive the eye to be?) proves that
we _must_ get beyond it. Even supposing that the whole operation were
transacted within the eye, and that the visible body were nowhere but
within the eye, still the eye which we invariably and inevitably fill in
as belonging to the visible body, (and no other eye is ever thought of or
spoken of by us,)--_this_ eye, we say, must necessarily exclude the
visible body, and all other visible things, from its sphere. Or, can the
eye (always conceived of as a visible thing among other visible things)
again contain the very phenomenon (_i.e._ the visible body) within which
it is itself contained? Surely no one will maintain a position of such
unparalleled absurdity as that.

The science of optics, in so far as it maintains, according to certain
physiological principles, that in the operation of seeing we never get
beyond the representations within the eye, is founded on the assumption,
that the visible body has no visible eye belonging to it. Whereas we
maintain, that the only eye that we have--the only eye we can form any
conception of, is the visible eye that belongs to the visible body, as a
part does to a whole; whether this eye be originally revealed to us by the
touch, by the sight, by the reason, or by the imagination. We maintain,
that to affirm we never get beyond this eye in the exercise of vision, is
equivalent to asserting, that a part is larger than the whole, of which it
is only a part--is equivalent to asserting, that Y, which is contained
between X and Z, is nevertheless of larger compass than X and Z, and
comprehends them both. The fallacy we conceive to be this, that the
visible body can be contained within the eye, without the eye of the
visible body also being contained therein. But this is a procedure, which
no law, either of thought or imagination, will tolerate. If we turn the
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