 FACT: The gasbag of Izzys airship is far too small to lift a  carriage of that size. Using hydrogen gas, it would take a spherical  balloon about 36 feet in diameter to lift a ton. The weight of four  passengers alone comes to over half that. Furthermore, at the end of  the film, Izzy was using hot air (as evidenced by the burner and the  open hole at the bottom of the bag), which is even less buoyant.  (The gas Izzy referred to had to have been hydrogen, since helium  was unavailable for airship use outside the United States until the  1950s).