Читать книгу Five Weeks in a Balloon - Jules Verne - Страница 20

chapter 10

Prior efforts—the doctor’s five tanks—the gas burner—the heating system—method of maneuvering—guaranteed success.

“People have often attempted, gentlemen, to rise or descend at will without wasting a balloon’s gas or ballast. A French balloonist, Monsieur Meusnier, tried to achieve this objective by pumping air into a bag inside the envelope. A Belgian, Dr. Van Hecke, used wings and windmill blades to work up a vertical force that in most cases wouldn’t have been sufficient. The practical results achieved by these different methods have been unimpressive.

“So I decided to tackle the problem more realistically. And at the outset I eliminated ballast from the equation, except in dealing with acts of God such as damage to my mechanism or the need to rise suddenly in order to dodge an unforeseen obstacle.

“My method of ascending and descending involves nothing more than changing the temperature to make the gas expand or contract inside my lighter-than-air vehicle. And here’s how I achieve this result.

“You saw several tanks brought on board along with the gondola, tanks whose functions are a mystery to you. There are five of them.

“The first holds about 25 gallons of water, to which I add a few drops of sulfuric acid to increase its ability to conduct electricity, and I break it down using a powerful Bunsen battery. You know the gases that make up water: it’s two parts hydrogen and one part oxygen.

“When the battery is in operation, the oxygen makes its way via the positive pole into a second tank. A third, positioned above the second and twice its capacity, receives the hydrogen reaching it via the negative pole.

“Spigots—one with an opening twice as big as the other’s—put these two tanks in contact with a fourth known as the mixing tank. There the two gases we get by breaking down water are indeed mixed. The capacity of this mixing tank is about 41 cubic feet.¹

“The upper part of this tank has a pipe made of platinum and equipped with a spigot.

“You can already see what we have, gentlemen: the mechanism I’ve described to you is nothing less than a kind of blowtorch—it’s a burner fed by oxygen and hydrogen, and it’s hotter than a furnace in a foundry.

“That settled, I’ll move on to the second part of the mechanism.

“Two roughly adjacent pipes emerge from the lower part of my balloon, which is hermetically sealed. One comes from the upper reaches of the hydrogen gas, the other from the lower reaches.

“These two pipes are equipped at various points with strong rubber joints, which allow them to flex as the vehicle shakes and shivers.

“Both of them go down into the gondola and vanish into a cylindrical tank made of iron and known as the heating tank. Two strong disks of the same metal close it off at both ends.

“The pipe from the balloon’s lower regions penetrates into this cylindrical container through its bottom disk; inside, it takes the form of a spiral-shaped coil whose rings rise one above the other, reaching almost to the top of the tank. Before emerging, the coil makes its way into a little cone whose convex base² is lowermost and looks like a bowl-shaped skullcap.

“The second pipe emerges from the peak of this cone and makes its way, as I’ve told you, into the balloon’s upper reaches.

“The bowl-shaped skullcap on the little cone is made of platinum to keep it from melting while the burner is in operation. That’s because the burner sits at the bottom of the iron tank in the middle of the spiral-shaped coil, and the tip of its flame will gently lick at this skullcap.

“You’re familiar with those heating systems, gentlemen, that are designed to warm apartments. You’re familiar with how they work. The air in an apartment is driven through its pipes and sent back out at a higher temperature. Now then, what I’ve just described to you is, in all honesty, simply one of those heating systems.

“What will actually take place? Once the burner is lit, the hydrogen in the coil and the convex cone heats up and swiftly rises through the pipe leading to the upper regions of my lighter-than-air vehicle. The vacuum created below draws the gas from the lower regions, warms it in turn, and is continually refilled; in the pipes and coil, then, there’s a tremendously swift stream of gas that keeps emerging from the balloon, returning to her, and heating back up.

“Now then, the gases will increase by ³ of their volume for every additional degree of heat. So if I make the temperature 18 degrees hotter,⁴ the hydrogen in my lighter-than-air vehicle will expand by , or 1,674 cubic feet,⁵ so it will displace an extra 1,674 cubic feet of air, which will increase my lifting power by 160 pounds. It’s the same, then, as dropping that amount of ballast. If I increase the temperature by 180 degrees,⁶ the gas will expand by : it will displace an extra 16,740 cubic feet, and my lifting power will be 1,600 pounds greater.

“As you can appreciate, gentlemen, it’s easy for me to significantly impact my buoyancy. I’ve calculated the volume of my lighter-than-air vehicle so that when she’s half inflated, she displaces a weight of air exactly equal to the envelope with its hydrogen plus the gondola with its travelers and all its accessories. Reaching this stage of her inflation, she’s at a point of perfect buoyancy in the air and neither climbs nor descends.

“To get her to ascend, I use my burner to make the gas hotter than the surrounding air; this additional heat builds up more pressure and further inflates the balloon, which keeps climbing the more her hydrogen expands.

“Naturally I descend by reducing the heat from my burner and letting the temperature cool back down. Generally it takes much less time to ascend than to descend. But that’s a lucky state of affairs; I’ve never put much stock in descending quickly, whereas, by contrast, a swift upward movement lets me dodge obstacles. The dangers are down below, not up above.

“Besides, as I’ve told you, I have a nominal amount of ballast that will let me rise even more swiftly if I need to. My valve, which is located at the very top of the balloon, is nothing more than a safety valve. The balloon always has the same amount of hydrogen; the changes in temperature that I produce inside this imprisoned gas are enough in themselves to move me upward and downward.

“Now, gentlemen, as a practical detail, I’ll add this one thing.

“The combustion of hydrogen and oxygen at the tip of the burner produces nothing but water vapor. So I’ve equipped the lower part of the cylindrical iron tank with an exhaust pipe that has a valve operating at a pressure less than two atmospheres; consequently, as soon as the steam reaches this intensity, it escapes on its own.

“And now let’s carefully run the numbers.

“Twenty-five gallons of water, broken down into its constituent elements, will give 200 pounds of oxygen and 25 pounds of hydrogen. This represents, with the atmospheric pressure, 1,890 cubic feet of the first and 3,780 cubic feet of the second, or 5,670 cubic feet for the whole mix.⁷

“Now then, when my burner’s spigot is wide open, it uses up 27 cubic feet per hour,⁸ and its flame is at least six times brighter than the biggest streetlights. So on an average, to keep myself at a middling altitude, I wouldn’t burn more than 9 cubic feet per hour;⁹ therefore my 25 gallons of water offer me 630 hours of airborne travel, or just over twenty-six days.

“And yet, since I can descend at will and replenish my water supply on the way, my journey can be of indefinite duration.

“That’s my secret, gentlemen; it’s simple, and as simple things do, it will succeed without fail. My method consists of making the gas expand and contract in my lighter-than-air vehicle, and there’s no need for clumsy wings or driving devices. A heating system to produce my changes in temperature, a burner to supply the heat—nothing that’s inconvenient or burdensome. So I believe that I’ve assembled all the prime ingredients for success.”

That was the close of Dr. Fergusson’s speech, and it was heartily applauded. There wasn’t a single objection to be raised; everything had been anticipated and resolved.

“Even so,” the commander said, “there could be some dangers.”

“If it works,” the doctor merely replied, “who cares?”