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210
The Fairy-Land of Science
·
Arabella B. Buckley
120
If
we
can
prevent
the
sound-wave
from
spreading,
then
the
sound
is
not
weakened.
The
Frenchman
Biot
found
that
a
low
whisper
could
be
heard
distinctly
for
a
distance
of
half
a
mile
through
a
tube,
because
the
waves
could
not
spread
beyond
the
small
column
of
air.
But
unless
you
speak
into
a
small
space
of
some
kind,
you
cannot
prevent
the
waves
going
out
from
you
in
all
directions.
Try
and
imagine
that
you
see
these
waves
spreading
all
round
me
now
and
hitting
on
your
ears
as
they
pass,
then
on
the
ears
of
those
behind
you,
and
on
and
on
in
widening
globes
till
they
reach
the
wall.
What
will
happen
when
they
get
there?
If
the
wall
were
thin,
as
a
wooden
partition
is,
they
would
shake
it,
and
it
again
would
shake
the
air
on
the
other
side,
and
so
anyone
in
the
next
room
would
have
the
sound
of
my
voice
brought
to
their
ear.
But
something
more
will
happen.
In
any
case
the
sound-waves
hitting
against
the
wall
will
bound
back
from
it
just
as
a
ball
bounds
back
when
thrown
against
anything,
and
so
another
set
of
sound-waves
reflected
from
the
wall
will
come
back
across
the
room.
If
these
waves
come
to
your
ear
so
quickly
that
they
mix
with
direct
waves,
they
help
to
make
the
sound
louder
in
this
room
than
you
would
in
the
open
air,
for
the
"Ha"
from
my
mouth
and
a
second
"Ha"
from
the
wall
come
to
your
ear
so
instantaneously
that
they
make
one
sound.
This
is
why
you
can
often
hear
better
at
the
far
end
of
a
church
when
you
stand
against
a
screen
or
a
wall,
then
when
you
are
half-way
up
the
building
nearer
to
the
speaker,
because
near
the
wall
the
reflected
waves
strike
strongly
on
your
ear
and
make
the
sound
louder.
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