the ear is in any sense the cause of
sight and hearing he seems hardly to be aware.

The process of sight is the most complicated (Rep.), and consists of
three elements--the light which is supposed to reside within the eye,
the light of the sun, and the light emitted from external objects. When
the light of the eye meets the light of the sun, and both together meet
the light issuing from an external object, this is the simple act of
sight. When the particles of light which proceed from the object are
exactly equal to the particles of the visual ray which meet them from
within, then the body is transparent. If they are larger and contract
the visual ray, a black colour is produced; if they are smaller and
dilate it, a white. Other phenomena are produced by the variety and
motion of light. A sudden flash of fire at once elicits light and
moisture from the eye, and causes a bright colour. A more subdued light,
on mingling with the moisture of the eye, produces a red colour. Out
of these elements all other colours are derived. All of them are
combinations of bright and red with white and black. Plato himself tells
us that he does not know in what proportions they combine, and he is of
opinion that such knowledge is granted to the gods only. To have seen
the affinity of them to each other and their connection with light, is
not a bad basis for a theory of colours. We must remember that they were
not distinctly defined to his, as they are to our eyes; he saw them, not
as they are divided in the prism, or artificially manufactured for the
painter's use, but as they exist in nature, blended and confused with
one another.

We can hardly agree with him when he tells us that smells do not admit
of kinds. He seems to think that no definite qualities can attach to
bodies which are in a state of transition or evaporation; he also makes
the subtle observation that smells must be denser than air, though
thinner than water, because when there is an obstruction to the
breathing, air can penetrate, but not smell.

The affections peculiar to the tongue are of various kinds, and, like
many other affections, are caused by contraction and dilation. Some of
them are produced by rough, others by abstergent, others by inflammatory
substances,--these act upon the testing instruments of the tongue, and
produce a more or less disagreeable sensation, while other particles
congenial to the tongue soften and harmonize them. The instruments of
taste