Today, ballooning may seem like a simple endeavor. We all understand how a balloon can carry the difference between its weight (including its enclosed gas) and the weight of the air that it displaces… as well as how the buoyancy of a hot-air balloon is controlled by heating the air in the balloon or by changing the amount of ballast (extra weight). But on November 21, 1783, when men were able to fly over Paris in a hot air balloon, it seemed like a miracle.
The first untethered manned balloon ascent took place on November 21, 1783, when two Frenchmen climbed into a wicker basket suspended from the base of a beautifully decorated, paper-lined cotton balloon. The balloon, filled with air heated by burning straw, carried the men aloft for a little more than 20 minutes over Paris. Witnessing this ascension were Louis XVI, members of the French Academy of Sciences, and multitudes of the public, including the American inventor and statesman Benjamin Franklin.
The Montgolfier brothers, a keystone in the development of the hot air balloon, came from a large family in Annonay, France that had been successful in the paper making business for generations. Working in the paper mill, the brothers noticed that smoke tended to rise, and that it could lift pieces of paper. The brothers made several unsuccessful balloon experiments indoors first. They filled a paper bag with steam, which just made the bag soggy. The brothers had heard of Henry Cavendish’s work showing that hydrogen was much lighter than air, and were eager to put that knowledge to use to lift objects into the air, but they couldn’t devise a way to contain the hydrogen.
Their first successful balloon was a bag made of paper and linen, open at the bottom. A fire held at the bottom heated the air in the bag. The heated air inside the bag expanded, making it less dense than the surrounding air, causing the bag to rise.
The Montgolfier brothers didn’t quite understand the physics involved– they believed thick smoke was the key to keeping the bag aloft, so they burned things like straw, wool, and even old shoes to produce the densest possible smoke. Not recognizing that the heat had made the bag rise, the brothers also seem to have believed at the time that they had produced a new, previously undiscovered gas that was lighter than air.
But even with their poor understanding, through trial and error they were able to produce a working balloon. After making several small-scale tests, they were ready for the first public demonstration. The ten-meter diameter balloon was exhibited on June 4, 1783. Tethered to the ground, and carrying no passengers, the balloon rose high above the marketplace at Annonay.
Sparked by their success, but too cautious to fly themselves, the Montgolfier brothers planned another demonstration, this time with a sheep, a duck, and a rooster as passengers on September 19, 1783.
On November 21, 1783, the balloon was ready for the first human passengers. Although King Louis XVI said he wanted to send prisoners on this potentially dangerous experiment, physicist Pilatre de Rozier volunteered for the honor of being the first to fly in an untethered hot air balloon.
This event left a profound impression on the world of the 18th century: men had actually flown! Since that time the field of flight has been taken over by airships, gliders, airplanes, helicopters, and even rockets and spacecraft, but balloons continue to be used for recreation, competitive sport, and scientific exploration.
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