Plato's Timaeus

TIMAEUS

by Plato

Translated by Benjamin Jowett

Section 7.

In Plato's explanation of sensation we are struck by the fact that he has
not the same distinct conception of organs of sense which is familiar to
ourselves. The senses are not instruments, but rather passages, through
which external objects strike upon the mind. The eye is the aperture
through which the stream of vision passes, the ear is the aperture through
which the vibrations of sound pass. But that the complex structure of the
eye or 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 reach from the tongue to the heart. Plato has a lively sense of the
manner in which sensation and motion are communicated from one part of the
body to the other, though he confuses the affections with the organs.
Hearing is a blow which passes through the ear and ends in the region of
the liver, being transmitted by means of the air, the brain, and the blood
to the soul. The swifter sound is acute, the sound which moves slowly is
grave. A great body of sound is loud, the opposite is low. Discord is
produced by the swifter and slower motions of two sounds, and is converted
into harmony when the swifter motions begin to pause and are overtaken by
the slower.

The general phenomena of sensation are partly internal, but the more
violent are caused by conflict with external objects. Proceeding by a
method of superficial observation, Plato remarks that the more sensitive
parts of the human frame are those which are least covered by flesh, as is
the case with the head and the elbows. Man, if his head had been covered
with a thicker pulp of flesh, might have been a longer-lived animal than he
is, but could not have had as quick perceptions. On the other hand, the
tongue is one of the most sensitive of organs; but then this is made, not
to be a covering to the bones which contain the marrow or source of life,
but with an express purpose, and in a separate mass.