Five Weeks in a Balloon. Jules Verne

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?”

      chapter 11

      Arriving in Zanzibar—the English consul—hostile reception by the natives—Koumbeni Island—the rainmakers—inflating the balloon—departure on April 18—final farewell—the Victoria.

      A continually favorable wind meant that the Resolute made excellent time to her port of destination. The Mozambique Channel was especially smooth sailing. This trip through the waves was a good omen for their trip through the clouds. Everybody was eager for the moment when they would arrive and put the finishing touches on Dr. Fergusson’s preparations.

      Finally the vessel came in sight of Zanzibar, the town located on the island of the same name, and at eleven o’clock in the morning on April 15, she dropped anchor in the harbor.

      The island of Zanzibar belongs to the Imam of Muscat, an ally of France and England, and it’s clearly his prize colony. The harbor welcomes a large number of ships from neighboring regions.

      The island is separated from Africa’s coast by a channel, no more than thirty miles across¹ at its widest point.

      It does a booming business in gum, ivory, and especially “ebony,” because Zanzibar is the leading slave market. This is the gathering place for all the conquered booty from the battles continually indulged in by chieftains inland. This trafficking in humanity also extends along the entire east coast, even up to the latitudes of the Nile, and Monsieur G. Lejean has seen this trade openly carried on under the flag of France.

      As soon as the Resolute arrived, the English consul in Zanzibar came on board to put himself at the doctor’s disposal, since, over the past month, European newspapers had kept him up to date on Fergusson’s plans. But until then he had belonged to the sizable phalanx of the skeptical.

       View of Zanzibar

      “I had my doubts,” he said, holding out his hand to Samuel Fergusson, “but not anymore.”

      He offered his own home to the doctor, Dick Kennedy, and of course our gallant Joe.

      As a further kindness, he acquainted the doctor with various letters he had received from Captain Speke. The captain and his companions had suffered dreadfully from hunger and foul weather before reaching the country of Ugogo; they found it tremendously difficult to make any headway and no longer thought they could send back news in a timely manner.

      “Those are perils and hardships we’ll be able to avoid,” the doctor said.

      The three travelers had their baggage transferred to the consul’s home. The crew got ready to unload the balloon on the beach in Zanzibar; there was a promising location next to the signal mast and near an enormous edifice that would shelter it from easterly winds. It was a huge tower shaped like an upended