In November 1782, while living in Avignon, Joseph started experimenting with small models made of wood and taffeta under which he lit a small fire. When the model rose, Joseph concluded that the smoke from the fire contained ‘Montgolfier Gas’ that had a special property he called ‘levity’. This phenomenon had been known since 1709 when a Brazilian priest, Bartolomeu de Gusmão, made a ball rise to the ceiling of the hall of the Casa da India, Lisbon, in the presence of King John V of Portugal. Despite being made a professor at the University of Coimbra, de Gusmão never developed a large scale lighter-than-air-ship.
Encouraged by his initial results, Joseph Montgolfier sent for Étienne, who had trained in Paris as an architect and thus had the ability to take Joseph’s experiments forward. Indeed, within a month of the initial experiment, the brothers had constructed a device with twenty-seven times the volume of the original model which flew with such force that they could not maintain control of it. They eventually found their experiment around two kilometres away.
On 4th June 1783, the brothers were ready for their first public demonstration. They readied their balloon in the marketplace at Annanoy. The balloon was made from sackcloth, lined on the inside with layers of paper and had a volume of 28,000 cubic feet. The enormous device drew a sizeable crowd, including local dignitaries, who watched the ten minute flight. The brothers became famous overnight.
Étienne went to Paris to conduct further demonstrations in collaboration with Jean-Baptiste Réveillon, the famous wallpaper manufacturer. The result was the Aerostat Réveillon, which flew in September 1783 carrying a sheep, a rooster and a duck aloft watched by King Louis XVI, his Queen, Marie Antoinette, and a very large crowd gathered at Versailles. Two months later, following successful test flights with human passengers in tethered balloons, Pilatre de Rozier and Marquis d’Arlandes became the first humans to make an untethered balloon flight from Château de la Muette, Paris.