t produce them, except in so
far as they are objects of sense themselves.

Physiology speaks to us of the wonderful apparatus of nerves, muscles,
tissues, by which the senses are enabled to fulfil their functions. It
traces the connexion, though imperfectly, of the bodily organs with the
operations of the mind. Of these latter, it seems rather to know the
conditions than the causes. It can prove to us that without the brain we
cannot think, and that without the eye we cannot see: and yet there is
far more in thinking and seeing than is given by the brain and the eye.
It observes the 'concomitant variations' of body and mind. Psychology,
on the other hand, treats of the same subject regarded from another
point of view. It speaks of the relation of the senses to one another;
it shows how they meet the mind; it analyzes the transition from sense
to thought. The one describes their nature as apparent to the outward
eye; by the other they are regarded only as the instruments of the mind.
It is in this latter point of view that we propose to consider them.

The simplest sensation involves an unconscious or nascent operation
of the mind; it implies objects of sense, and objects of sense have
differences of form, number, colour. But the conception of an object
without us, or the power of discriminating numbers, forms, colours,
is not given by the sense, but by the mind. A mere sensation does not
attain to distinctness: it is a confused impression, sugkechumenon ti,
as Plato says (Republic), until number introduces light and order
into the confusion. At what point confusion becomes distinctness is a
question of degree which cannot be precisely determined. The distant
object, the undefined notion, come out into relief as we approach
them or attend to them. Or we may assist the analysis by attempting
to imagine the world first dawning upon the eye of the infant or of a
person newly restored to sight. Yet even with them the mind as well
as the eye opens or enlarges. For all three are inseparably bound
together--the object would be nowhere and nothing, if not perceived by
the sense, and the sense would have no power of distinguishing without
the mind.

But prior to objects of sense there is a third nature in which they
are contained--that is to say, space, which may be explained in various
ways. It is the element which surrounds them; it is the vacuum or void
which they leave or occupy when passing from one portion of space to
an