Therefore, if all creatures on or around the earth were
without ears or nerves of hearing, there would be no instrument
on which to play, and consequently there would be no such thing
as sound. This proves that two things are needed in order that
we may hear. First, the outside movement which plays on our
hearing instrument; and, secondly, the hearing instrument itself.
First, then, let us try to understand what happens outside our
ears. Take a poker and tie a piece of string to it, and holding
the ends of the string to your ears, strike the poker against the
fender. You will hear a very loud sound, for the blow will set
all the particles of the poker quivering, and this movement will
pass right along the string to the drum of your ear and play upon
it.
Now take the string away from you ears, and hold it with your
teeth. Stop your ears tight, and strike the poker once more
against the fender. You will hear the sound quite as loudly and
clearly as you did before, but this time the drum of your ear has
not been agitated.
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