THE VOICES OF NATURE. 147 
fro by the clouds on their road; and in the mountains 
we know how the peals echo and re-echo till they die 
away. 
We might filLup far more than an hour in speaking 
of those voices which come to us as nature is at work. 
Think of the patter of the rain, how each drop as it 
hits the pavement sends circles of sound-waves out on 
all sides ; or the loud report which falls on the ear of 
the Alpine traveller as the glacier cracks on its way 
down the valley ; or the mighty boom of the avalanche 
as the snow slides in huge masses off the side of the 
lofty mountain. Each and all of these create their 
sound-waves, large or small, loud or feeble, which 
make their way to your ear, and become converted 
into sound. 
We have, however, only time now just to glance at 
life-sounds, of which there are so many around us. 
Do you know why we hear a buzzing, as the gnat, the 
bee, or the cockchafer fly past ? Not by the beating 
of their wings against the air, as many people imagine, 
and as is really the case with humming birds, but by 
the scraping of the under-part of their hard wings 
against the edges of their hind-legs, which are toothed 
like a saw. 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. 
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