Early flying machines a second, inner ballonet. On 19 September 1784, it completed the first flight of over , between Paris and Beuvry, despite the man-powered propulsive devices proving useless. In January the next year Jean Pierre Blanchard and John Jeffries crossed the English Channel from Dover to the Bois de Felmores in a Charlière. But a similar attempt the other way ended in tragedy. In an attempt to provide both endurance and controllability, de Rozier developed a balloon with both hot air and hydrogen gas bags, a design which was soon named after him as the "Rozière." His idea was to use
Hot air balloon control line that runs to the basket. A parachute vent is opened by pulling on the control line. Once the control line is released, the pressure of the remaining hot air pushes the vent fabric back into place. A parachute vent can be opened briefly while in flight to initiate a rapid descent. (Slower descents are initiated by allowing the air in the balloon to cool naturally.) The vent is pulled open completely to collapse the balloon after landing. An older, and presently less commonly used, style of top vent is called a "Velcro-style" vent. This too is a disk