THE VOICES OF NATURE. 139 
whenever the stirrup hits at the little window, the 
fluid moves these hairs to and fro, and they irritate 
the ends of a nerve *, and this nerve carries the mes- 
sage to your brain. There are also some curious little 
stones called otoliths, lying in some parts of this fluid, 
and they, by their rolling to and fro, probably keep up 
the motion and prolong the sound. 
You must not imagine we have explained here the 
many intricacies which occur in the ear ; I can only 
hope to give you a rough idea of it, so that you may 
picture to yourselves the air-waves moving (as in 
Fig. 32) backwards and forward in the canal of your 
ear, then the tympanum vibrating to and fro, the 
hammer hitting the anvil, the stirrup knocking at the 
little window, the fluid waving the fine hairs and rolling 
the tiny stones, the ends of the nerve quivering, and 
then (how we know not) the brain hearing the message. 
Is not this wonderful, going on as it does at every 
sound you hear ? And yet this is not all, for inside 
that curled part of the labyrinth g, which looks like a 
snail-shell and is called the cochlea, there is a most 
wonderful apparatus of more than three thousand fine 
stretched filaments or threads, and these act like the 
strings of a harp, and make you hear different tones. 
If you go near to a harp or a piano, and sing any- 
particular note very loudly, you will hear this note 
sounding in the instrument, because you will set just 
that particular string quivering, which gives the note 
you sang. The air-waves set going by your voice 
touch that string, because it can quiver in time with 
them, while none of the other strings can do so. Now, 
just in the same way the tiny instrument of three 
