This year marks the 200th anniversary of “Gay-Lussac’s two remarkable balloon ascents,” writes Foil A. Miller of Pittsburgh in the spring issue of Philatelia Chimica et Physica [26, 92 (2004)], the journal of the chemistry-and-physics-on-stamps study unit of the American Topical Association. Joseph L. Gay-Lussac, a pioneer of hot-air ballooning, discovered the second ideal gas law: The volume of a given mass of gas is directly proportional to its temperature.
A second pioneer of hot-air ballooning, Jacques A. C. Charles, also discovered the second law, in about 1787, but never bothered to publish. Gay-Lussac found the law independently in 1801–02. Thus the law is known both as Charles’ law and as Gay-Lussac’s law.
Back to ballooning. The French brothers Joseph M. and Jacques E. Montgolfier invented the hot-air balloon. Miller writes, “Joseph, while drying his wife’s chemise over a fire, realized that the same gas that raised and billowed the cloth might send aloft a large sack tied to a laundry basket.” He and his brother thought it was the smoke that did the job, but no matter. The Montgolfiers built a 33-foot-diameter balloon and fueled it with a smoke-producing mixture of damp straw, wool, and old shoes. They launched the contraption on June 5, 1783, near Lyon. It rose to about 1,500 feet but settled to the ground about 1.5 miles away after some 10 minutes in the air.
On Aug. 27 of the same year, Charles, a French professor of physics, released at Paris the first hydrogen-filled balloon. He needed four days to make enough hydrogen. The balloon vanished into the clouds at about 1,500 feet and landed some 45 minutes later in a moderately distant village. It terrified the peasants, who attacked it with pitchforks and then tied it to a donkey that dragged it through the village.
Ballooning had become all the rage in Paris, Miller reports, and people were clamoring for the first manned ascent. King Louis XVI’s historian, Pilâtre de Rozier, went up several times in a tethered hot-air balloon and showed that you could keep the fire going while aloft. De Rozier and the Marquis d’Arlandes made the first manned free-balloon flight on Nov. 21, 1783. The balloon floated about 5.5 miles over Paris in about 25 minutes. The observers included Louis XVI, Marie Antoinette, Benjamin Franklin, and some 40,000 French people.
Ten days later, on Dec. 1, 1783, Charles and M. N. Robert launched the first manned hydrogen balloon. It rose to 2,000 feet, stayed up for 2.5 hours, and drifted 27 miles.
During the early 1800s, Miller writes, the Russians reported that Earth’s magnetic field decreases with increasing distance from Earth. On Aug. 24, 1804, Gay-Lussac and physicist Jean B. Biot went up in a hot-air balloon to check out the Russian idea. All iron was excluded, excepting a few tools hung on a string far below the open basket. The basket contained, besides the humans, a sheep, a rooster, pigeons, snakes, bees, and other insects. The scientists began making observations at about 8,600 feet and rose no higher than 13,100 feet despite jettisoning everything they could spare. They landed about 48 miles from Paris after 3.5 hours aloft. They found no variation in Earth’s magnetic field.
Gay-Lussac went up alone on Sept. 16, 1804. He reached 23,000 feet, Miller says, as calculated from barometric pressure. Gay-Lussac sampled the air at different altitudes and found no change in composition. His altitude record stood for half a century.
The items jettisoned on the foregoing flight included an old kitchen chair. The balloon was invisible in the clouds. The chair landed near a girl tending sheep, and she screamed. The local priest was consulted, but he could opine only that the chair had fallen from heaven or been thrown out by angels. The mystery went away a few days later when news of the balloon reached the village, which was about 20 miles from Paris.
Hot air in balloons was replaced by hydrogen and later helium. During the 1960s, however, hot-air ballooning returned as a sport, Miller says. Propane heaters and synthetic fabrics have helped. Today, Miller writes, “hot-air balloons are a common sight in many communities on calm mornings and evenings. One of [my] sons has recently earned his hot-air balloon license.”