the hot air balloon
While
some were dreaming of flying like a bird, others
preferred to take it one step at a time and
simply try to lift into the air.
The idea of using Archimedes’ buoyancy
principle to rise in the
atmosphere by creating an object
lighter than the air it displaces had been introduced in
1670 by a Jesuit priest,
Father Francesco de Lana of
Brescia, Italy. De Lana suggested (in print) that
copper could be used to
create spheres thin enough to be light-
weight yet strong enough to be
evacuated of all air,
thereby making the total sphere lighter than the air the
sphere displaced. The
theory was sound, but producing
sufficiently light spheres that would not collapse under
the pressure of the air
proved too difficult. In 1766, the
British scientist Henry Cavendish discovered
hydrogen gas (as the product of mixing iron, tin,
zinc shavings, and sulfuric acid) and found it to
be one-tenth the weight of air. This should have
stirred someone to realize that
hydrogen gas could be used to fill
a balloon and the result would be a
lighter-than-air object. Inexplicably, it did not, and the
first balloons to fly were filled with hot air.

Barthelmy-Laurent de Gusman’s flying boat, from a 1709
engraving. The craft was to
be kept aloft by
magnets in the two globes fore and
aft. How this was to
be accomplished was never explained.

Adding
sulphuric acid to iron filings
creates
hydrogen, as
illustrated by this
eighteenth-century
drawing.
In the mid-1770s, Joseph and Etienne
Montgolfier, brothers who worked in their father’s paper
factory in Annonay in South-Eastern France, noted that paper
rose in the updrafts of the factory’s chimney, and
occasionally a sheet would fold into a dome and continue
rising even after leaving the immediate area of the
chimney. They conducted some simple experiments with silk
bags and soon became convinced that a large bag with heated
air inside would rise. In actuality, this effect had already
been demonstrated nearly seventy-five years earlier by the
Brazilian priest C Bartolomeu de Guasmao, who conducted a
spectacular demonstration in the court of King John V in
Lisbon, Portugal. But the Montgolfiers knew nothing of this
demonstration, and they knew little about the reason their
balloon rose into the air. They believed that the balloon
was filled with a gas they called “Montgolfier gas” that had
a special property they called “levity.” They did not even
associate heated air with Montgolfier gas—they believed that
the levity was contained in the smoke. Still, the
Montgolfiers conducted their experiments and trials with
care and learned much from each trial run.
After experimenting with smaller models, they constructed a
large balloon of linen covered with stiff paper—prints of
the time show a large blue ovoid, brightly decorated and
held together with buttons—and conducted many trials,
beginning on April 25, 1783 (the first known date), and
culminating in a public demonstration in the town square of
Annonay on June 5. Etienne was immediately summoned to Paris
to address the Academy of Sciences about the brothers’
invention. Even before Etienne arrived, the French physicist
Jacques Charles, mistakenly believing the Montgolfiers had
used hydrogen in their ascent, hastily constructed a balloon
of varnished silk, filled it with hydrogen (an expensive
chemical procedure on such a large scale), and launched it
from the Champs de Mars, Paris, on August 27. It rose
through heavy rains that fell that day and was carried away
by the storm to the village of Gonesse some fifteen miles
(24km) away, where it finally came to rest.
The superstitious peasants of the village, believing the
balloon to be a monster that was attacking them from the
sky, proceeded to rip it to shreds with scythes and
pitchforks. The flight of the first “Charliere,” as
hydrogen-filled balloons were to be called for many
years afterwards, had therefore been a qualified success.
The Montgolfier brothers then built an even larger
balloon—some seventy feet (21m) high—equipped with a
circular gallery for the aeronauts. Two adventurers,
Jean-Francois Pilatre de Rozier and Francois Laurent,
Marquis d’Arandes, volunteered for the flight, which was
prepared for and anticipated with the same nail-biting
nervousness that characterized the first manned rocket
launches of modern times.
Tests were conducted with animals to determine what possible
ill effects there might be on living beings, and then,
beginning on October 15, tethered flights with humans were
conducted from the courtyard of the Palace of Versailles. On
November 21, the same pair made a free (un-tethered) flight
in their Montgolfier, landing about ten miles (16km)
away about twenty-three minutes after launching.
That event is often considered the
first time humankind flew.

The
Charles hydrogen balloon, which was
launched on August 27, 1783, was ripped to shreds by
the fearful townsmen of
Gonesse
On December 1, Charles and his associate, Nicolas
Robert launched a new hydrogen balloon
from the Tuileries Gardens.
They landed twenty-seven miles
(43.5km) away after a flight of two
hours, and except for the
fact that the balloon took off again with Charles
when Robert abruptly jumped
out of the gondola after their
first landing (only to land several miles away), filling a
balloon with hydrogen was quickly seen as the
superior method: it did not require constant
attention to a heat source
to warm the air (and anyway, the heat
source was a smoky mess
since the Montgolfiers refused to
accept Charles’ instruction that it was merely the
heated air that was carrying their craft aloft and not the
smoke). The explosive nature of hydrogen was not to become
important until years later, when very large volumes of
hydrogen were placed in close proximity to flames and
sparks.

The throng that
gathered to watch the historic flight of Montgolfier’s
crewed balloon on November21 was less superstitious.
The French
wasted no time exploiting the new technology. Eleven years
later, in France’s war
with Austria, tethered
balloons were used in the siege of Mainz and
were decisive at the Battle of
Fleurus. The captain of the
Company of Aerostiers was a man named Coutelle, a
shadowy figure who was
ridiculed for espousing the use of
balloons on the battlefield. After France’s victory, he
became a national hero. De Lana had foreseen the
possible military uses of his flying evacuated
copper globes, and feared
flight for “the disturbance it would cause to
the civil government of
men.” It took more than a century, but his words proved
prophetic.
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