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On The Soul   

the power to set in movement what is already actually transparent,

and, as we have seen, the actuality of what is transparent is just


The following experiment makes the necessity of a medium clear. If

what has colour is placed in immediate contact with the eye, it cannot

be seen. Colour sets in movement not the sense organ but what is

transparent, e.g. the air, and that, extending continuously from the

object to the organ, sets the latter in movement. Democritus

misrepresents the facts when he expresses the opinion that if the

interspace were empty one could distinctly see an ant on the vault

of the sky; that is an impossibility. Seeing is due to an affection or

change of what has the perceptive faculty, and it cannot be affected

by the seen colour itself; it remains that it must be affected by what

comes between. Hence it is indispensable that there be something in

between-if there were nothing, so far from seeing with greater

distinctness, we should see nothing at all.

We have now explained the cause why colour cannot be seen

otherwise than in light. Fire on the other hand is seen both in

darkness and in light; this double possibility follows necessarily

from our theory, for it is just fire that makes what is potentially

transparent actually transparent.

The same account holds also of sound and smell; if the object of

either of these senses is in immediate contact with the organ no

sensation is produced. In both cases the object sets in movement

only what lies between, and this in turn sets the organ in movement:

if what sounds or smells is brought into immediate contact with the

organ, no sensation will be produced. The same, in spite of all

appearances, applies also to touch and taste; why there is this

apparent difference will be clear later. What comes between in the

case of sounds is air; the corresponding medium in the case of smell

has no name. But, corresponding to what is transparent in the case

of colour, there is a quality found both in air and water, which

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