A balloon filled with any gas which is less dense than air will rise in the atmosphere. This is because the mass of the air displaced by the balloon is greater than the mass of the balloon itself. Since the density of the atmosphere decreases with increasing altitude, the balloon rises until the mass of the balloon and its load equals the mass of the air displaced by the balloon. At this point the balloon floats in the atmosphere.
Two French scientists, Jacques Charles and Joseph Gay-Lussac, were pioneers in the use of balloons. They made some of the first studies measuring the properties of gases. The first balloon flight had been made in France by the Montgolfier brothers in June 1783 using a hot-air balloon.
A few months later in August of the same year Charles filled a balloon with hydrogen which he made by the reaction of about 250 kg of acid and 500 kg of iron! The balloon remained in the air for 45 minutes and traveled a distance of about 25 km.
In 1803 Joseph Gay-Lussac set a record by ascending to 7 km (23,000 ft). He used balloon flights to carry out experiments such as studies of the composition of the atmosphere and variations in the earth’s magnetic field. Hydrogen-filled balloons have continued to be used for weather observations up to the present day. Because of the very low density of hydrogen, they can reach heights of approximately 40 km.
By the 1930s a logical development of the hydrogen balloon, the airship, was providing regular transportation across the Atlantic. Instead of just drifting in the wind, airships were driven by engine-powered propellers and included cabins for passengers. The disastrous fire that destroyed the German airship Hindenburg in 1937 marked the end of the airship era.
However, the possibility of building airships that use helium, which is nonflammable but expensive, has attracted new interest. Although they would be too slow to compete with jets, helium airships might have other uses, such as transporting timber in forestry operations.