o be associated with the eye, and how the particular visual
sensations come to be associated with something distant from the eye:
and further, how this association of the condition with one thing, and
of the sensations with another thing, (an association established by the
touch and not by the sight,) dissolves the primary synthesis of seeing
and colours. It is to be observed that there are two stages in the
process by which this secernment is brought about--_First_, the stage in
which the visual phenomena are associated with things different from the
organ of vision, the very existence of which is as yet unknown. Let us
suppose, then, the function of sight to be in operation. We behold a
visible object--a particular colour. Let the touch now come into play.
We feel a tangible object--say a book. Now from the mere fact of the
visible and the tangible object being seen and felt together, we could
not associate them in place; for it is quite possible that the tangible
object may admit of being withdrawn, and yet the visible object remain:
and if so, no association of the two in place can be established. But
this is a point that can only be determined by experience; and what says
that wise instructor? We withdraw the tangible object. The visible
object, too, disappears: it leaves its place. We replace the tangible
object--the visible object reappears _in statu quo_. There is no
occasion to vary the experiment. If we find that the visible object
invariably leaves its place when the tangible object leaves its, and
that the one invariably comes back when the other returns, we have
brought forward quite enough to establish an inevitable association in
place between the two. The two places are henceforth regarded, not as
two, but as one and the same.

By the aid of the touch, then, we have associated the visual phenomena
with thing which are _not_ the organ of vision; and well it is for us
that we have done so betimes, and before we were aware of the eye's
existence. Had the eye been indicated to us in the mere act of seeing;
had we become apprised of its existence _before_ we had associated our
visual sensations with the tangible objects constituting the material
universe, the probability, nay the certainty, is that we would have
associated them with this eye, and that then it would have been as
impossible for us to break up the association between colours and the
organ, as it now is for us to dissolve the union between colours