An echo occurs, when, a mass of air having been unified,
bounded, and prevented from dissipation by the containing
walls of a vessel, the air originally struck by the impinging body
and set in movement by it rebounds from this mass of air like a
ball from a wall. It is probable that in all generation of sound
echo takes place, though it is frequently only indistinctly heard.
What happens here must be analogous to what happens in the
case of light; light is always reflected – otherwise it would not
be diffused and outside what was directly illuminated by the
sun there would be blank darkness; but this reflected light is
not always strong enough, as it is when it is reflected from
water, bronze, and other smooth bodies, to cast a shadow, which
is the distinguishing mark by which we recognize light.
What has the power of producing sound is what has the power
of setting in movement a single mass of air which is continuous
from the impinging body up to the organ of hearing. The organ
of hearing is physically united with air, and because it is in air,
the air inside is moved concurrently with the air outside. Hence
animals do not 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.
In some cases there is no discrepancy of any sort in the names
used, but a difference of kind between the meanings is at once
obvious: e.g. in the case of ‘clear’ and ‘obscure’: for sound is
called ‘clear’ and ‘obscure’, just as ‘colour’ is too. As regards the
names, then, there is no discrepancy, but the difference in kind
between the meanings is at once obvious: for colour is not
called ‘clear’ in a like sense to sound.
Further, see in regard
to their intermediates, if some meanings and their contraries
have an intermediate, others have none, or if both have one but
not the same one, e.g. ‘clear’ and ‘obscure’ in the case of colours
have ‘grey’ as an intermediate, whereas in the case of sound
they have none, or, if they have, it is ‘harsh’, as some people say
that a harsh sound is intermediate. ‘Clear’, then, is an
ambiguous term, and likewise also ‘obscure’. See, moreover, if
some of them have more than one intermediate, while others
have but one, as is the case with ‘clear’ and ‘obscure’, for in the
case of colours there are numbers of intermediates, whereas in
regard to sound there is but one, viz. ‘harsh’.
The void is thought to be place with nothing in it. The reason
for this is that people take what exists to be body, and hold that
while every body is in place, void is place in which there is no
body, so that where there is no body, there must be void.
Every body, again, they suppose to be tangible; and of this
nature is whatever has weight or lightness.
Hence, by a syllogism, what has nothing heavy or light in it, is
void.
This result, then, as I have said, is reached by syllogism. It
would be absurd to suppose that the point is void; for the void
must be place which has in it an interval in tangible body.
But at all events we observe then that in one way the void is
described as what is not full of body perceptible to touch; and
what has heaviness and lightness is perceptible to touch. So we
would raise the question: what would they say of an interval
that has colour or sound – is it void or not? Clearly they would
reply that if it could receive what is tangible it was void, and if
not, not.
From all this it is clear that the theory that the movement of the stars
produces a harmony, i.e. that the sounds they make are concordant,
in spite of the grace and originality with which it has been stated, is
nevertheless untrue. Some thinkers suppose that the motion of
bodies of that size must produce a noise, since on our earth the
motion of bodies far inferior in size and in speed of movement has
that effect. Also, when the sun and the moon, they say, and all the
stars, so great in number and in size, are moving with so rapid a
motion, how should they not produce a sound immensely great?
Starting from this argument and from the observation that their
speeds, as measured by their distances, are in the same ratios as
musical concordances, they assert that the sound given forth by the
circular movement of the stars is a harmony. Since, however, it
appears unaccountable that we should not hear this music, they
explain this by saying that the sound is in our ears from the very
moment of birth and is thus indistinguishable from its contrary
There is not only the absurdity of our hearing nothing, the ground of
which they try to remove, but also the fact that no effect other than
sensitive is produced upon us. Excessive noises, we know, shatter the
solid bodies even of inanimate things: the noise of thunder, for
instance, splits rocks and the strongest of bodies. But if the moving
bodies are so great, and the sound which penetrates to us is
proportionate to their size, that sound must needs reach us in an
intensity many times that of thunder, and the force of its action must
be immense. Indeed the reason why we do not hear, and show in our
bodies none of the effects of violent force, is easily given: it is that
there is no noise. But not only is the explanation evident; it is also a
corroboration of the truth of the views we have advanced. For the
very difficulty which made the Pythagoreans say that the motion of
the stars produces a concord corroborates our view.
Indeed, this must be recognized as the cause of the fire that is
generated in the earth: the air is first broken up in small
particles and then the wind is beaten about and so catches fire.
A phenomenon in these islands affords further evidence of the
fact that winds move below the surface of the earth. When a
south wind is going to blow there is a premonitory indication: a
sound is heard in the places from which the eruptions issue.
This is because the sea is being pushed on from a distance and
its advance thrusts back into the earth the wind that was
issuing from it. The reason why there is a noise and no
earthquake is that the underground spaces are so extensive in
proportion to the quantity of the air that is being driven on that
the wind slips away into the void beyond.
Subterranean noises, too, are due to the wind; sometimes they
portend earthquakes but sometimes they have been heard
without any earthquake following. Just as the air gives off
various sounds when it is struck, so it does when it strikes other
things; for striking involves being struck and so the two cases
are the same. The sound precedes the shock because sound is thinner and passes through things more readily than wind. But
when the wind is too weak by reason of thinness to cause an
earthquake the absence of a shock is due to its filtering through
readily, though by striking hard and hollow masses of different
shapes it makes various noises, so that the earth sometimes
seems to ‘bellow’ as the portentmongers say
But if any of the dry exhalation is caught in the process as the
air cools, it is squeezed out as the clouds contract, and collides
in its rapid course with the neighbouring clouds, and the sound
of this collision is what we call thunder. This collision is
analogous, to compare small with great, to the sound we hear in
a flame which men call the laughter or the threat of Hephaestus
or of Hestia. This occurs when the wood dries and cracks and
the exhalation rushes on the flame in a body. So in the clouds,
the exhalation is projected and its impact on dense clouds
causes thunder: the variety of the sound is due to the
What is capable of taking on colour is what in itself is
colourless, as what can take on sound is what is soundless;
what is colourless includes (a) what is transparent and (b) what
is invisible or scarcely visible, i.e. what is ‘dark’. The latter (b) is
the same as what is transparent, when it is potentially, not of
course when it is actually transparent; it is the same substance
which is now darkness, now light.
Sound may mean either of two things (a) actual, and (b)
potential, sound. There are certain things which, as we say,
‘have no sound’, e.g. sponges or wool, others which have, e.g.
bronze and in general all things which are smooth and solid –
the latter are said to have a sound because they can make a
sound, i.e. can generate actual sound between themselves and
the organ of hearing.
Actual sound requires for its occurrence (i, ii) two such bodies
and (iii) a space between them; for it is generated by an impact.
Hence it is impossible for one body only to generate a sound –
there must be a body impinging and a body impinged upon;
what sounds does so by striking against something else, and
this is impossible without a movement from place to place.
Actual sound requires for its occurrence (i, ii) two such bodies
and (iii) a space between them; for it is generated by an impact.
Hence it is impossible for one body only to generate a sound –
there must be a body impinging and a body impinged upon;
what sounds does so by striking against something else, and
this is impossible without a movement from place to place.
As we have said, not all bodies can by impact on one another
produce sound; impact on wool makes no sound, while the
impact on bronze or any body which is smooth and hollow
does. Bronze gives out a sound when struck because it is
smooth; bodies which are hollow owing to reflection repeat the
original impact over and over again, the body originally set in
movement being unable to escape from the concavity.
Further, we must remark that sound is heard both in air and in
water, though less distinctly in the latter. Yet neither air nor
water is the principal cause of sound. What is required for the
production of sound is an impact of two solids against one
another and against the air. The latter condition is satisfied
when the air impinged upon does not retreat before the blow,
i.e. is not dissipated by it.
That is why it must be struck with a sudden sharp blow, if it is
to sound – the movement of the whip must outrun the
dispersion of the air, just as one might get in a stroke at a heap
or whirl of sand as it was traveling rapidly past
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 what is
sharp really moves fast, and what is grave, slowly, but that the
difference in the qualities of the one and the other movement is
due to their respective speeds. There seems to be a sort of
parallelism between what is acute or grave to hearing and what
is sharp or blunt to touch; what is sharp as it were stabs, while
what is blunt pushes, the one producing its effect in a short, the
other in a long time, so that the one is quick, the other slow.
Voice then is the impact of the inbreathed air against the
‘windpipe’, and the agent that produces the impact is the soul
resident in these parts of the body. Not every sound, as we said,
made by an animal is voice (even with the tongue we may
merely make a sound which is not voice, or without the tongue
as in coughing); what produces the impact must have soul in it
and must be accompanied by an act of imagination, for voice is
a sound with a meaning, and is not merely the result of any