The hot air balloon became exceptionally popular during the late 18th century, which led to the discovery of the relationship between altitude and atmosphere.
The discovery of hydrogen in the 17th century led to the development of the first hydrogen balloon. In 1783, the Montgolfier brothers, including Jacques-Étienne and Joseph-Michel, flew the first unmanned hot air balloon over Annonay, France. The same year, they flew a piloted, tethered hot air balloon with Giroud de Villette, Jean-François Pilâtre de Rozier, and Jean-Baptiste Réveillon onboard. Later, they launched their first untethered hot air balloon flight, which flew nine kilometers in about 25 minutes. The hot air balloon became exceptionally popular during the late 18th century, which led to the discovery of the relationship between altitude and atmosphere. However, the main downside of hot air balloons was a lack of maneuverability.