144 THE FAIRY-LAND OF SCIENCE. 
is dashed on the ground, it explodes and sends 
sound-waves to your ear. Listen to the sea some 
day when the waves are high and stormy, and you 
cannot fail to be struck by the irregular bursts of 
sound. 
The waves, however, do not only roar as they dash 
on the ground ; have you never noticed how they seem 
to scream as they draw back down the beach ? Tenny- 
son calls it. 
" Fhe scream of the madden'd beach dragged down by the wave ;" 
and it is caused by the stones grating against each 
other as the waves drag them down. Dr. Tyndall 
tells us that it is possible to know the size of the 
stones by the kind of noise they make. If they 
are large, it is a confused noise ; when smaller, a 
kind of scream ; while a gravelly beach will produce a 
mere hiss. 
Who could be dull by the side of a brook, a water- 
fall, or the sea, while he Can listen for sounds like these, 
and picture to himself how they are being made ? You 
may discover a number of other causes of sound maoo 
by water, if you once pay attention to them. 
Nor is it only water that sings to us. Listen to 
the wind, how sweetly it sighs among the leaves. 
There we hear it, because it rubs the leaves together, 
and they produce the sound-waves. But walk against 
the wind some day and you can hear it whistling in 
your own ear, striking against the curved cup, and 
then setting up a succession of waves in the hearing 
canal of the ear itself. 
Why should it sound in one particular tone when 
