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172
Wonderful Balloon Ascents; Or, The Conquest of the Skies
·
Fulgence Marion
23
If
an
object
thrown
into
the
air
is
heavier
than
the
air
which
it
displaces,
it
descends,
and
falls
upon
the
earth;
if
it
is
of
equal
weight,
it
floats
without
rising
or
falling;
if
it
is
lighter,
it
rises
until
it
comes
to
a
stratum
of
air
of
less
weight
or
density
than
itself.
We
all
know,
of
course,
that
the
higher
you
rise
from
the
earth
the
density
of
the
air
diminishes.
The
stratum
of
air
that
lies
upon
the
surface
of
the
earth
is
the
heaviest,
because
it
supports
the
pressure
of
all
the
other
strata
that
lie
above.
Thus
the
lightest
strata
are
the
highest.
The
principle
of
the
construction
of
balloons
is,
therefore,
in
perfect
harmony
with
physical
laws.
Balloons
are
simply
globes,
made
of
a
light,
air-tight
material,
filled
with
hot
air
or
hydrogen
gas
which
rise
in
the
air
because
(they
are
lighter
than
the
air
they
displace).
The
application
of
this
principle
appeared
so
simple,
that
at
the
time
when
the
news
of
the
invention
of
the
balloon
was
spread
abroad
the
astronomer
Lalande
wrote--“At
this
news
we
all
cry,
‘This
must
be!
Why
did
we
not
think
of
it
before?’”
It
had
been
thought
of
before,
as
we
have
seen
in
the
last
chapter,
but
it
is
often
long
after
an
idea
is
conceived
that
it
is
practically
realised.
The
first
balloon,
Montgolfier’s,
was
simply
filled
with
hot
air;
and
it
was
because
Montgolfier
exclusively
made
use
of
hot
air
that
balloons
so
filled
were
named
Montgolfiers.
Of
course
we
see
at
a
glance
that
hot
air
is
lighter
than
cold
air,
because
it
has
become
expanded
and
occupies
more
space--that
is
to
say,
a
volume
of
hot
air
contains
actually
less
air
than
a
volume
of
the
same
size
of
air
that
has
not
been
heated.
The
difference
between
the
weight
of
the
hot
air
and
the
cold
which
it
displaced
was
greater
than
the
weight
of
tire
covering
of
the
balloon.
Therefore
the
balloon
mounted.
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