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210
The Fairy-Land of Science
·
Arabella B. Buckley
50
Having
now
learned
what
air
is,
the
next
question
which
presents
itself
is,
Why
does
it
stay
round
our
earth?
You
will
remember
we
saw
in
the
first
lecture,
that
all
the
little
atoms
of
a
gas
are
trying
to
fly
away
from
each
other,
so
that
if
I
turn
on
this
gas-jet
the
atoms
soon
leave
it,
and
reach
you
at
the
farther
end
of
the
room,
and
you
can
smell
the
gas.
Why,
then,
do
not
all
the
atoms
of
oxygen
and
nitrogen
fly
away
from
our
earth
into
space,
and
leave
us
without
any
air?
Ah!
here
you
must
look
for
another
of
our
invisible
forces.
Have
you
forgotten
our
giant
force,
"gravitation,"
which
draws
things
together
from
a
distance?
This
force
draws
together
the
earth
and
the
atoms
of
oxygen
and
nitrogen;
and
as
the
earth
is
very
big
and
heavy,
and
the
atoms
of
air
are
light
and
easily
moved,
they
are
drawn
down
to
the
earth
and
held
there
by
gravitation.
But
for
all
that,
the
atmosphere
does
not
leave
off
trying
to
fly
away;
it
is
always
pressing
upwards
and
outwards
with
all
its
might,
while
the
earth
is
doing
its
best
to
hold
it
down.
The
effect
of
this
is,
that
near
the
earth,
where
the
pull
downward
is
very
strong,
the
air-atoms
are
drawn
very
closely
together,
because
gravitation
gets
the
best
of
the
struggle.
But
as
we
get
farther
and
farther
from
the
earth,
the
pull
downward
becomes
weaker,
and
then
the
air-atoms
spring
farther
apart,
and
the
air
becomes
thinner.
Suppose
that
the
lines
in
this
diagram
represent
layers
of
air.
Near
the
earth
we
have
to
represent
them
as
lying
closely
together,
but
as
they
recede
from
the
earth
they
are
also
farther
apart.
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