In the Montgolfier brothers’ 1783 balloon experiment, heated air made their unmanned balloon rise.
Joseph-Michel and Jacques-Étienne Montgolfier built a large paper-and-linen balloon and demonstrated it publicly at Annonay, France, on 4 June 1783. A fire beneath the opening warmed the air inside the envelope, making the balloon buoyant because the heated air was less dense than the surrounding atmosphere.
The demonstration was unmanned, so it did not yet prove that people could safely fly. Later that year, the Montgolfiers conducted flights carrying animals and then human passengers. The first untethered human flight took place near Paris on 21 November 1783, using a larger hot-air balloon.
A common mix-up is to associate the first balloon flights with hydrogen. Jacques Charles launched a hydrogen-filled balloon in August 1783, only months after the Montgolfier demonstration. Hot-air balloons and gas balloons both rely on buoyancy, but they use different lifting gases and operating methods.