Hot air is less dense than cold air, which is why hot air rises. People have known that hot air rises (or at any rate that smoke, sparks and flames go upwards) from time immemorial, and the technology to make a hot air balloon has existed for thousands of years. Ancient Egyptian papyrus would have been almost ideal for the construction of the envelope of a hot air balloon, although so far no serious Egyptologist has suggested that the Ancient Egyptians actually made one.
The earliest surviving record of a hot air balloon so far discovered is in 1709 when a Jesuit monk called Gusmao demonstrated one to the King of Portugal. From what we know of Gusmao from other sources it is unlikely that this was either his first or his last experiment with hot air balloons but no other records survive.We usually credit the invention of the hot air balloon to the Montgolfier brothers. They lived in France. During the summer of 1783 they carried out a series of experiments on hot air balloons and then in September 1783 they demonstrated a hot air balloon carrying a sheep, a duck and a cockerel. Finally in November 1783 Pilatre de Rozier and the Maquis d'Arlandes made the first Manned hot air balloon flight in a Montgolfier balloon. These flights are very well documented.
Meanwhile, in another part of France, a Professor of science called Jacques Charles had read a rather garbled newspaper account of the Montgolfier brothers experiments with balloons. He had also read about the properties of hydrogen which had been discovered by the English chemist Cavendish a few years earlier, in 1766, and assumed that this is what the Montgolfier Brothers had used in their balloons. So he did some experiments of his own and in December 1783 he made a flight in a hydrogen balloon. His design was so right in every way that almost every hydrogen-filled balloon since then has been in all essential details identical to this balloon.
For the next few years there was intense rivalry between the advocates of Montgolfier (hot air) and Charlier (hydrogen) balloons although unfortunately not all reports on balloons from this period say what sort of balloon was being used, some even refer to all balloons as Montgolfiers. However, in the end the hydrogen balloon won because providing a really reliable supply of hot air proved too difficult, and in particular the fire needed to provide the hot air was not easy to control, and it was not uncommon for the envelope of a hot air balloon to catch alight - this did actually happen on the first Manned flight in November 1783! By the early 1800s the hot air balloon was dead, not to be revived again until the invention of the propane burner in 1960.
A few people, most notably de Rozier (who had made the first balloon flight with the Maquis d'Arlandes) saw the advantages of composite balloons, with one basket suspended from two envelopes, one containing hot air and one containing hydrogen. Unfortunately if the envelope of the hot air balloon caught fire, as in those days often happened even with ordinary hot air balloons, it was difficult to prevent the flames from spreading to the hydrogen balloon, and de Rozier was eventually killed when one of his composite balloons caught fire in this way while he was trying to cross the English Channel, and composite balloons were abandoned as being unsafe. They were revived in the 1970s, when the use of helium and the invention of the propane burner made them safe again. To link to a Page on composite (Rozier) balloons please click here
© Barry Gray March 2004