Sometimes the roll is made even longer by the echo, as
the sound-waves are reflected to and 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 fill up 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.
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