148 THE FAIRY-LAND OF SCIENCE. 
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 n6t 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. 
But if you will try some day in the woods you will 
find that a bird can beat you over and over again in 
the length of his note ; when you are out of breath 
and forced to stop he will go on with his merry trill 
as fresh and clear as if he had only just begun. This 
is because birds can draw air into the whole of their 
body, and they have a large stock laid up in the folds 
of their windpipe, and besides this the air-chamber 
behind their elastic bands or vocal chords has two 
compartments where we have only one, and the second 
compartment has special muscles by which they can 
open and shut it, and so prolong the trill. 
Only think what a rapid succession of waves must 
quiver through the air as a tiny lark agitates his little 
throat and pours forth a volume of song ! The next 
time you are in the country in the spring, spend half 
an hour listening to him, and try and picture to 
yourself how that little being is moving all the atmo- 
