Things Certain and Uncertain: The Montgolfiers’ Balloons

Aerostatic balloon flight, like powered airplane flight, involved considerable experimentation and preparation. Like the Wright brothers, the Montgolfier brothers devoted their time, talent, and funds to realizing their dream. The first progress was made by Joseph Montgolfier in November 1782, when he set aloft a hollow, taffeta-lined box by heating the interior air. This early experiment was limited, occurring only briefly and indoors. But it demonstrated the soundness of the basic principles, leading to an outdoor experiment the next month, in which a larger hot-air ballon rose to a height of 70 feet [Kotar and Gessler 2003, p. 10].

The famous 1783 demonstration at Versailles was the first balloon flight by living creatures, but it was not the Montgolfiers’ first public success. That honor resides with a 4 June 1783 flight at Annonay, in which a hot-air balloon was flown to a height of 3,000 feet and an eventual distance of about 1.7 miles. This early creation was made up of silk sections with paper backing, attached to a mostly-spherical frame 30 feet in diameter [Holmes 2008]. Unfortunately, it caught fire after landing in a vineyard and was consumed, to be replaced some months later by the Aérostat Réveillon. However, the flight caught the attention of the wider public, and news of its success reached St. Petersburg in August of that year [Gillispie 1983, p. 32].

The Montgolfiers came to the science of lighter-than-air flight through their family's connection to the paper manufacturing business. Their father, Pierre, ran a successful paper company in Annonay, and he later turned over control of the business to the elder son, Joseph. The young businessman also had a longstanding interest in the behavior of gases, having relied on his cousin Matthieu Duret as early as 1777 for information on Joseph Priestley and Henry Cavendish’s experiments on oxygen (then called “dephlogisticated air”) and hydrogen (“inflammable air”), respectively [Gillispie 1983, p. 15]. As Joseph wrote in a letter to Duret, “All that you have taught me of chemistry only confirms me more fully in my ideas. I must make some experiments” [Gillispie 1983, p. 15].

Figure 2. A detailed sketch of the Montgolfier brothers' Aérostat Réveillon, including
information on its height, diameter, volume, and weight. Library of Congress.

These experiments began in earnest in late 1782, during which time Joseph and his younger brother Étienne attempted no fewer than three balloon flights, each with varying degrees of success [Kotar and Gessler 2003, p. 10]. While not adept at the physical mechanics of their balloons, the Montgolfiers did have a basic understanding of their functioning. As the Journal de Paris reported on the Montgolfiers' flight at Annonay,

He had a globe constructed, 35 feet in diameter, with canvas mounted on a framework of wood and wire. . . . According to the calculation of M. Mongolfier, the globe occupied a space for which a volume of air would weigh 2,156 pounds; but since the gas only weighed 1,078 pounds and the globe 500 pounds, there was an excess of 578 pounds for the force with which the globe tended to rise [Journal de Paris 1783, pp. 861–862, translated by the authors].

The overall principle—that heated air occupying a fixed volume is less dense and thus less heavy—appears to have been at the front of the Montgolfiers' minds throughout this time. As we saw above, the successful flight of the Aérostat Réveillon at Versailles occurred only one year after their first balloons took to the air. Le Roy and other members and officials of the Paris Academy of Sciences reported on this flight and several others by the Montgolfier brothers. They co-authored a memoir that was read to the Academy on 23 December 1783 and published the following year as a monograph. In it, they described the Aérostat Reveillon's descent as having occurred "so gently that it merely bent the tree branches on which it landed, and the animals that were suspended from it did not suffer in the slightest" [Le Roy et al. 1784, p. 15, translated by the authors].