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The Fairy-Land of Science
·
Arabella B. Buckley
75
Perhaps
you
would
scarcely
imagine
at
first
that
it
is
this
screen
of
vapour
which
determines
whether
or
not
we
shall
have
dew
upon
the
ground.
Have
you
ever
thought
why
dew
forms,
or
what
power
has
been
at
work
scattering
the
sparkling
drops
upon
the
grass?
Picture
to
yourself
that
it
has
been
a
very
hot
summer's
day,
and
the
ground
and
the
grass
have
been
well
warmed,
and
that
the
sun
goes
down
in
a
clear
sky
without
any
clouds.
At
once
the
heat-
waves
which
have
been
stored
up
in
the
ground,
bound
back
into
the
air,
and
here
some
are
greedily
absorbed
by
the
vapour,
while
others
make
their
way
slowly
upwards.
The
grass,
especially,
gives
out
these
heat-waves
very
quickly,
because
the
blades,
being
very
thin,
are
almost
all
surface.
In
consequence
of
this
they
part
with
their
heat
more
quickly
than
they
can
draw
it
up
from
the
ground,
and
become
cold.
Now
the
air
lying
just
above
the
grass
is
full
of
invisible
vapour,
and
the
cold
of
the
blades,
as
it
touches
them,
chills
the
water-
particles,
and
they
are
no
longer
able
to
hold
apart,
but
are
drawn
together
into
drops
on
the
surface
of
the
leaves.
We
can
easily
make
artificial
dew
for
ourselves.
I
have
here
a
bottle
of
ice
which
has
been
kept
outside
the
window.
When
I
bring
it
into
the
warm
room
a
mist
forms
rapidly
outside
the
bottle.
This
mist
is
composed
of
water-drops,
drawn
out
of
the
air
of
the
room,
because
the
cold
glass
chilled
the
air
all
round
it,
so
that
it
gave
up
its
invisible
water
to
form
dew-drops.
Just
in
this
same
way
the
cold
blades
of
grass
chill
the
air
lying
above
them,
and
steal
its
vapour.
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