do you see now the reason why pan-pipes give
different sounds, or even the hole at the end of a common key
when you blow across it? Here is a subject you will find very
interesting if you will read about it, for I can only just
suggest it to you here. But now you will see that the canal of
your ear also answers only to certain waves, and so the wind
sings in your ear with a real if not a musical note.
Again, on a windy night have you not heard the wind sounding a
wild, sad note down a valley? Why do you think it sounds so much
louder and more musical here than when it is blowing across the
plain? Because air in the valley will only answer to a certain
set of waves, and, like the pan-pipe, gives a particular note as
the wind blows across it, and these waves go up and down the
valley in regular pulses, making a wild howl. You may hear the
same in the chimney, or in the keyhole; all these are waves set
up in the hole across which the wind blows. Even the music in
the shell which you hold to your ear is made by the air in the
shell pulsating to and fro.
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