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210
The Fairy-Land of Science
·
Arabella B. Buckley
59
Let
us
suppose
that
one
day
the
air
is
so
much
lighter
that
it
presses
down
only
with
a
weight
of
14
1/2
lbs.
to
the
square
inch
instead
of
15
lbs.
Then
the
mercury
would
fall
to
29
inches,
because
each
inch
is
equal
to
the
weight
of
half
a
pound.
Now,
when
the
air
is
damp
and
very
full
of
water-vapour
it
is
much
lighter,
and
so
when
the
barometer
falls
we
expect
rain.
Sometimes,
however,
other
causes
make
the
air
light,
and
then,
although
the
barometer
is
low,
no
rain
comes,
Again,
if
the
air
becomes
heavier
the
mercury
is
pushed
up
above
30
to
31
inches,
and
in
this
way
we
are
able
to
weigh
the
invisible
air-ocean
all
over
the
world,
and
tell
when
it
grows
lighter
or
heavier.
This
then,
is
the
secret
of
the
barometer.
We
cannot
speak
of
the
thermometer
today,
but
I
should
like
to
warn
you
in
passing
that
it
has
nothing
to
do
with
the
weight
of
the
air,
but
only
with
heat,
and
acts
in
quite
a
different
way.
And
now
we
have
been
so
long
hunting
out,
testing
and
weighing
our
aerial
ocean,
that
scarcely
any
time
is
left
us
to
speak
of
its
movements
or
the
pleasant
breezes
which
it
makes
for
us
in
our
country
walks.
Did
you
ever
try
to
run
races
on
a
very
windy
day?
Ah!
then
you
feel
the
air
strongly
enough;
how
it
beats
against
your
face
and
chest,
and
blows
down
your
throat
so
as
to
take
your
breath
away;
and
what
hard
work
it
is
to
struggle
against
it!
Stop
for
a
moment
and
rest,
and
ask
yourself,
what
is
the
wind?
Why
does
it
blow
sometimes
one
way
and
sometimes
another,
and
sometimes
not
at
all?
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