Page:Works of Jules Verne - Parke - Vol 1.djvu/255

Rh "From the lower part of my balloon, which is hermetically closed, two tubes pass out at a short distance from each other. One of these leads from the upper volume of hydrogen, the other from the lower. They both descend as far as the car, and terminate in a cylindrical iron chest called the heat chest. It is closed at each extremity by a strong disc of the same metal.

"The tube from the lower part of the balloon enters the cylindrical chest through the lower disc, and there assumes the shape of a coil, whose upper rings occupy nearly the entire height of the box. Before leaving the chest, the coil is led into a little cone, whose base, concave, like a round cap, is directed downwards.

"It is at the top of this cone that the second tube makes its exit, and it terminates, as I have said, in the upper folds of the balloon.

"The spherical cap of the little cone is made of platinum, so that it may not be melted under the action of the blowpipe, for this is placed at the bottom of the iron case in the center of the coil, and the flame lightly licks this cap.

"You know those stoves used for warming rooms? You know how they act? The air of the room is forced through the tubes and comes back warmer. So that what I have been describing is, after all, only a stove.

"And, in fact, what takes place? Once the blow-pipe is lighted, the hydrogen is warmed and rises rapidly by the tube to the upper part of the balloon. A vacuum is caused below, and the gas from the lower part is attracted to fill it, which, in its turn, is warmed, and is continually replaced, so that an extremely rapid current of gas is generated, leaving the balloon, returning, and being warmed without cessation.

"Now, gases increase 1/480 of their volume for every degree of heat. If, then, I create a temperature of 18°, the hydrogen in the balloon will increase 18/480, or 1,614 cubic feet; it will then displace 1,674 cubic feet of air more, which will increase its power of ascent 160 pounds. That comes, then, to the same weight of ballast. If I increase the temperature to 180°, the gas expands 180/480, it displaces 6,740 cubic feet, and the ascending force amounts to 1,600 pounds.

"You can understand, gentlemen, that I am easily able to obtain considerable changes of equilibrium. The volume of my balloon has been calculated in such a way that, when half