ich the expressive thing borrows an interest; and
we shall speak of the intrinsic quality of forms as their emotional
tinge or specific value.

_Physiology of the perception of form._

Sec. 20. The charm of a line evidently consists in the relation of its
parts; in order to understand this interest in spatial relations, we
must inquire how they are perceived.[4] If the eye had its sensitive
surface, the retina, exposed directly to the light, we could never
have a perception of form any more than in the nose or ear, which
also perceive the object through media. When the perception is not
through a medium, but direct, as in the case of the skin, we might
get a notion of form, because each point of the object would excite
a single point in the skin, and as the sensations in different parts of
the skin differ in quality, a manifold of sense, in which
discrimination of parts would be involved, could be presented to
the mind. But when the perception is through a medium, a
difficulty arises.

Any point, a, in the object will send a ray to every point, _a', b',
c',_ of the sensitive surface; every point of the retina will therefore
be similarly affected, since each will receive rays from every part
of the object.

[Illustration of light rays]

If all the rays from one point of the object, a, are to be concentrated
on a corresponding point of the retina, a which would then
become the exclusive representative of a, we must have one or
more refracting surfaces interposed, to gather the rays together.
The presence of the lens, with its various coatings, has made
representation of point by point possible for the eye. The absence
of such an instrument makes the same sort of representation
impossible to other senses, such as the nose, which does not smell
in one place the effluvia of one part of the environment and in
another place the effluvia of another, but smells indiscriminately
the combination of all. Eyes without lenses like those possessed by
some animals, undoubtedly give only a consciousness of diffused
light, without the possibility of boundaries or divisions in the field
of view. The abstraction of colour from form is therefore by no
means an artificial one, since, by a simplification of the organ of
sense, one may be perceived without the other.

But even if the lens enables the eye to receive a distributed image
of the object, the manifold which consciousness would perceive
would not be necessarily a manifold of