Colour print entitled 'A Profesor Filling and Explaining to an Audience the Nature of a Balloon'. Hot-air balloons are based on the simple scientific principle that hot air rises. Hot air is lighter than cool air because it has les mas per unit of volume. The Montgolfier Brothers were amongst the first to succesfully exploit this idea, experimenting by inflating paper balloons using the hot air produced by straw fires. They were unaware what made the balloon rise, however, crediting this miracle to the discovery of an unknown gas, which became known as 'Montgolfier's gas'. Hot-air was soon replaced by the lifting gas hydrogen, after Charles and Robert's succesful ascent in a hydrogen balloon in 1783 proved its supremacy. Dimensions: 119mm x 170mm.
© Science Museum / Science & Society Picture Library