range of all its other sensations. By imagining the
sight as a sensation of colour, we diminish it to a speck within the
sphere of its own sensations; and as we now regard the sense as for ever
enclosed within this small embrasure, all the other sensations which were
its, previous to our discovery of the organ, and which are its still, are
built up into a world of objective existence, _necessarily_ external to
the sight, and altogether out of its control. All sensations of colour are
necessarily out of one another. Surely, then, when the sight is subsumed
under the category of colour--as it unquestionably is whenever we think of
the eye--surely all other colours must, of necessity, assume a position
external to it; and what more is wanting to constitute that real objective
universe of light and glory in which our hearts rejoice?

We can, perhaps, make this matter still plainer by reverting to our old
illustration. Our first exposition of the question was designed to exhibit
a general view of the case, through the medium of a dead symbolical figure.
This proved nothing, though we imagine that it illustrated much. Our
second exposition exhibited the illustration in its application to the
living sphere of sensation _in general_; and this proved little. But we
conceive that therein was foreshadowed a certain procedure, which, if it
can be shown from experience to be the actual procedure of sensation _in
detail_, will prove all that we are desirous of establishing. We now, then,
descend to a more systematic exposition of the process which (so far as
our experience goes, and we beg to refer the reader to his own) seems to
be involved in the operation of seeing. We dwell chiefly upon the sense of
sight, because it is mainly through its ministrations that a real
objective universe is given to us. Let the circle A be the whole circuit
of vision. We may begin by calling it the eye, the retina, or what we will.
Let it be provided with the ordinary complement of sensations--the colours
X Y Z. Now, we admit that these sensations cannot be extruded beyond the
periphery of vision; and yet we maintain that, unless they be made to fall
on the outside of that periphery, they cannot become real objects. How is
this difficulty--this contradiction--to be overcome? Nature overcomes it,
by a contrivance as simple as it is beautiful. In the operation of seeing,
admitting the canvass or background of our picture to be a retina, or what
we will,