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On The Soul   

hear with all parts of their bodies, nor do all parts admit of the

entrance of air; for even the part which can be moved and can sound

has not air everywhere in it. Air in itself is, owing to its

friability, quite soundless; only when its dissipation is prevented is

its movement sound. The air in the ear is built into a chamber just to

prevent this dissipating movement, in order that the animal may

accurately apprehend all varieties of the movements of the air

outside. That is why we hear also in water, viz. because the water

cannot get into the air chamber or even, owing to the spirals, into

the outer ear. If this does happen, hearing ceases, as it also does if

the tympanic membrane is damaged, just as sight ceases if the membrane

covering the pupil is damaged. It is also a test of deafness whether

the ear does or does not reverberate like a horn; the air inside the

ear has always a movement of its own, but the sound we hear is

always the sounding of something else, not of the organ itself. That

is why we say that we hear with what is empty and echoes, viz. because

what we hear with is a chamber which contains a bounded mass of air.

Which is it that 'sounds', the striking body or the struck? Is not

the answer 'it is both, but each in a different way'? Sound is a

movement of what can rebound from a smooth surface when struck against

it. As we have explained' not everything sounds when it strikes or

is struck, e.g. if one needle is struck against another, neither emits

any sound. In order, therefore, that sound may be generated, what is

struck must be smooth, to enable the air to rebound and be shaken

off from it in one piece.

The distinctions between different sounding bodies show themselves

only in actual sound; as without the help of light colours remain

invisible, so without the help of actual sound the distinctions

between acute and grave sounds remain inaudible. Acute and grave are

here metaphors, transferred from their proper sphere, viz. that of

touch, where they mean respectively (a) what moves the sense much in a

short time, (b) what moves the sense little in a long time. Not that

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