The more
rapidly their wings move the stronger the grating sound becomes,
and you will now see why in hot, thirsty weather the buzzing of
the gnat is so loud, for the more thirsty and the more eager he
becomes, the wilder his movements will be.
Some insects, like the drone-fly (Eristalis tenax), force the air
through the tiny air-passages in their sides, and as these
passages are closed by little plates, the plates vibrate to and
fro and make sound-waves. Again, what are those curious sounds
you may hear sometimes if you rest your head on a trunk in the
forest? They are made by the timber-boring beetles, which saw
the wood with their jaws and make a noise in the world, even
though they have no voice.
All these life-sounds are made by creatures which do not sing or
speak; but the sweetest sounds of all in the woods are the voices
of the birds. All voice-sounds are made by two elastic bands or
cushions, called vocal chords, stretched across the end of the
tube or windpipe through which we breathe, and as we send the air
through them we tighten or loosen them as we will, and so make
them vibrate quickly or slowly and make sound-waves of different
lengths.
Pages:
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200