The oldest aerial sport, ballooning was inaugurated by the French Montgolfier brothers in 1783 with a hot-air balloon. Once launched, a balloon rises until its average density equals that of the surrounding atmosphere. To go higher, the pilot must discard some ballast. To descend, the pilot releases some of the buoyant gas through a valve. The 19-century balloonists' great dream was intercontinental air travel. John Wise, a 19th century American balloonist detected a constant current of wind that he was certain would carry him across the ocean to Europe. He was killed in a ballooning accident before he could make his attempt. The current of wind he identified now is known as the jet stream.