A treat! Not one but four stamps today, all nearly together with the original perforations. The theme is hot air ballooning and we have the Intrepid from 1861 on the left and the Explorer II from 1935 on the right.
Explorer II was a manned balloon which reached a record altitude of 22,066m (72,395 ft) in November 1935. Its predecessor Explorer had reached 18,475m the previous year before rips in the canopy led the crew to reduce altitude. A spark then ignited the hydrogen leading to a rapid plummet to the ground (the crew got out just in time). This and a similar crash in Russia led to a slowing in the race for balloon altitude, but the US started up again in 1935, this time using helium instead of hydrogen. Explorer II took 8 hours to inflate, stood 96m tall when inflated and its crew became the first people to see the curvature of the earth.
The Intrepid was more humble but more immediately useful. It was one of seven balloons used for manned reconnaissance during the American Civil War. It enabled the Union Army to look down on battefields and relay intelligence about troop movements via onboard telegraph equipment.
It’s easy to forget in our plane-based era, but “lighter-than-air” flight was seen as having more potential than heavier-than-air planes well into the 20th century.