When the surface on which it impinges is quite smooth, what is
produced by the original impact is a united mass, a result due to
the smoothness of the surface with which the air is in contact at
the other end.
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.
Pages:
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74