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 445 experiment, the system would require me to take up too much water. The surface of the balloon is so great that the mass of the steam, instead of condensing and falling in drops as it ought to do, seems simply to disappear, to escape through the varnished silk, where gas itself cannot escape. At least this is what happened to me.

Yet such heating of one’s gas is too tempting an idea to be abandoned, especially in these days of perfected petroleum fuel. With one kilogramme of petroleum I am promised by the manufacturers of my boilers and condensers that I can vaporise twenty kilogrammes of water. If I can devise a practical means for catching this water again as it ceases to be steam, the oft-studied problem will be solved. Imagine the balloon to be coming down—the result of gas condensation. Instead of lightening it by throwing out twenty kilogrammes of sand, I will have but to burn one kilogramme of petroleum! My twenty kilogrammes of water will become steam, itself lighter than the air, and whose heat will dilate my gas to such an extent as to produce thirty kilogrammes of new ascensional force !

At first I hoped that the thing could be accomplished by means of a small and very tight steam-bag sewed inside the balloon. I would lead my steam to it, there to condense and fall in drops which could be caught, by means of a tube. This steam-bag, expanding as it filled, would have at the same time served as an interior air-ballonet to aid in maintaining the balloon's form, Unfortunately no silk and varnish will resist steam, and after long experiments in which the steam reduced my steam-bags to a sticky mass, I hit upon my present condensers.

Why should I not lead from the boiler directly to a present-day aluminium condenser hung inside the balloon? It had never been done—but that is the distinguishing particular of all new things. Now I have done it. You can call it a condenser or a radiator ; in fact, it differs little from the radiator of an automobile in construction or function, though its object is to heat instead of to cool. It consists of half a kilometre of very thin aluminium tubes disposed vertically in the form of a hollow cone, the whole being suspended inside the balloon from its top.

Now imagine the balloon to be in the air—and coming down as the result of gas condensation. I simply turn a faucet, and steam immediately generated by a remarkable little up-to-date boiler begins mounting to the condenser and rushing through its half a kilometre of tubes. This steam cannot possibly mingle with my gas, yet it heats it, re-dilates it, and gives new ascensional power to the balloon. Indeed, the radiation of the half a kilometre of tubes is so complete that the steam ceases to