THE FUTURE OF AIR-SHIPS.
throw out enough ballast to correspond to the ascensional force lost by such condensation, you will begin descending to earth. If you throw out too much ballast, you will become too light again and shoot up too high.
Imagine you have thrown out just enough. All goes well for a time. Then the little cloud ceases to mask the sun. Your gas will heat up again, and by its dilatation will regain its old lifting power ; but, having less to lift by the amount of ballast just thrown out, it will dart higher into the air, where the decreasing atmospheric pressure will permit it to go on dilating until a lot of gas escapes through the valve with which every balloon is furnished. Otherwise the balloon would burst !
You have overshot your equilibrium and lost too much gas—because the balloon is an impetuous thing, always exaggerating. Therefore you will find yourself descending—to condense your gas again as the atmospheric pressure increases—when more ballast must be sacrificed, and the balloon shoots up too high again, and the trouble recommences !
The skill of the spherical balloonist consists precisely in maintaining his desired altitude with the greatest economy of gas and ballast ; but, be he ever so exact, the time must come when repeated condensations have forced him to throw out his last gramme of ballast and repeated dilatations have lost him so much gas that the balloon sinks to earth—no longer spherical, but pearshaped, with its lower part hanging flaccid.
From the earliest ballooning times, men have sought to combat condensation by means of heat. Montgolfier's first balloon was filled with nothing but hot air, which is lighter than the cool air of the atmosphere ; and it has always been known than an adequate heating of one's gas would be equivalent to saving so much ballast.
Pilâtre de Rozier who, accompanied by the Marquis d'Arlandes, was the first in the world to make a free balloon ascent, finally lost his life in an attempt to cross the English Channel by means of such a contrivance in which heated air was to reinforce hydrogen gas.
Many methods have been since proposed, the latest and most logical being a plan which would allow steam to freely mingle with one's gas—the theory being that such steam will condense in drops on the inside surface of the balloon envelope, to be caught again without loss they fall into a proper receptacle below the open vent at the bottom of the spherical balloon.
Nothing could be more logical or beautiful than this plan in theory and the only reasons I have for refusing to adopt it in practice come from my own small experiments, which I do not claim to be conclusive. Only, so far as I have been able to
