by Jules Verne
CHAPTER TENTH.
Former Experiments.--The Doctor's Five Receptacles.--The GasCylinder.--The Calorifere.--The System of Manoeuvring.--Success certain.
"The attempt has often been made, gentlemen," said the doctor, "to riseand descend at will, without losing ballast or gas from the balloon. AFrench aeronaut, M. Meunier, tried to accomplish this by compressing airin an inner receptacle. A Belgian, Dr. Van Hecke, by means of wingsand paddles, obtained a vertical power that would have sufficed in mostcases, but the practical results secured from these experiments havebeen insignificant.
"I therefore resolved to go about the thing more directly; so, at thestart, I dispensed with ballast altogether, excepting as a provision forcases of special emergency, such as the breakage of my apparatus, orthe necessity of ascending very suddenly, so as to avoid unforeseenobstacles.
"My means of ascent and descent consist simply in dilating orcontracting the gas that is in the balloon by the application ofdifferent temperatures, and here is the method of obtaining that result.
"You saw me bring on board with the car several cases or receptacles,the use of which you may not have understood. They are five in number.
"The first contains about twenty-five gallons of water, to which I adda few drops of sulphuric acid, so as to augment its capacity as aconductor of electricity, and then I decompose it by means of a powerfulBuntzen battery. Water, as you know, consists of two parts of hydrogento one of oxygen gas.
"The latter, through the action of the battery, passes at its positivepole into the second receptacle. A third receptacle, placed above thesecond one, and of double its capacity, receives the hydrogen passinginto it by the negative pole.
"Stopcocks, of which one has an orifice twice the size of the other,communicate between these receptacles and a fourth one, which iscalled the mixture reservoir, since in it the two gases obtained by thedecomposition of the water do really commingle. The capacity of thisfourth tank is about forty-one cubic feet.
"On the upper part of this tank is a platinum tube provided with astopcock.
"You will now readily understand, gentlemen, the apparatus that I havedescribed to you is really a gas cylinder and blow-pipe for oxygen andhydrogen, the heat of which exceeds that of a forge fire.
"This much established, I proceed to the second part of my apparatus.From the lowest part of my balloon, which is hermetically closed, issuetwo tubes a little distance apart. The one starts among the upper layersof the hydrogen gas, the other amid the lower layers.
"These two pipes are provided at intervals with strong jointings ofindia-rubber, which enable them to move in harmony with the oscillationsof the balloon.
"Both of them run down as far as the car, and lose themselves in aniron receptacle of cylindrical form, which is called the heat-tank. Thelatter is closed at its two ends by two strong plates of the same metal.
"The pipe running from the lower part of the balloon runs into thiscylindrical receptacle through the lower plate; it penetrates the latterand then takes the form of a helicoidal or screw-shaped spiral, therings of which, rising one over the other, occupy nearly the whole ofthe height of the tank. Before again issuing from it, this spiral runsinto a small cone with a concave base, that is turned downward in theshape of a spherical cap.
"It is from the top of this cone that the second pipe issues, and itruns, as I have said, into the upper beds of the balloon.
"The spherical cap of the small cone is of platinum, so as not to meltby the action of the cylinder and blow-pipe, for the latter are placedupon the bottom of the iron tank in the midst of the helicoidalspiral, and the extremity of their flame will slightly touch the cap inquestion.
"You all know, gentlemen, what a calorifere, to heat apartments, is. Youknow how it acts. The air of the apartments is forced to pass throughits pipes, and is then released with a heightened temperature. Well,what I have just described to you is nothing more nor less than acalorifere.
"In fact, what is it that takes place? The cylinder once lighted, thehydrogen in the spiral and in the concave cone becomes heated, andrapidly ascends through the pipe that leads to the upper part of theballoon. A vacuum is created below, and it attracts the gas in the lowerparts; this becomes heated in its turn, and is continually replaced;thus, an extremely rapid current of gas is established in the pipes andin the spiral, which issues from the balloon and then returns to it, andis heated over again, incessantly.
"Now, the cases increase 1/480 of their volume for each degree of heatapplied. If, then, I force the temperature 18 degrees, the hydrogen ofthe balloon will dilate 18/480 or 1614 cubic feet, and will, therefore,displace 1614 more cubic feet of air, which will increase itsascensional power by 160 pounds. This is equivalent to throwing out thatweight of ballast. If I augment the temperature by 180 degrees, the gaswill dilate 180/480 and will displace 16,740 cubic feet more, and itsascensional force will be augmented by 1,600 pounds.
"Thus, you see, gentlemen, that I can easily effect very considerablechanges of equilibrium. The volume of the balloon has been calculatedin such manner that, when half inflated, it displaces a weight of airexactly equal to that of the envelope containing the hydrogen gas,and of the car occupied by the passengers, and all its apparatus andaccessories. At this point of inflation, it is in exact equilibrium withthe air, and neither mounts nor descends.
"In order, then, to effect an ascent, I give the gas a temperaturesuperior to the temperature of the surrounding air by means of mycylinder. By this excess of heat it obtains a larger distention, andinflates the balloon more. The latter, then, ascends in proportion as Iheat the hydrogen.
"The descent, of course, is effected by lowering the heat of thecylinder, and letting the temperature abate. The ascent wouldbe, usually, more rapid than the descent; but that is a fortunatecircumstance, since it is of no importance to me to descend rapidly,while, on the other hand, it is by a very rapid ascent that I avoidobstacles. The real danger lurks below, and not above.
"Besides, as I have said, I have a certain quantity of ballast, whichwill enable me to ascend more rapidly still, when necessary. My valve,at the top of the balloon, is nothing more nor less than a safety-valve.The balloon always retains the same quantity of hydrogen, and thevariations of temperature that I produce in the midst of this shut-upgas are, of themselves, sufficient to provide for all these ascendingand descending movements.
"Now, gentlemen, as a practical detail, let me add this:
"The combustion of the hydrogen and of the oxygen at the point of thecylinder produces solely the vapor or steam of water. I have, therefore,provided the lower part of the cylindrical iron box with a scape-pipe,with a valve operating by means of a pressure of two atmospheres;consequently, so soon as this amount of pressure is attained, the steamescapes of itself.
"Here are the exact figures: 25 gallons of water, separated into itsconstituent elements, yield 200 pounds of oxygen and 25 pounds ofhydrogen. This represents, at atmospheric tension, 1,800 cubic feet ofthe former and 3,780 cubic feet of the latter, or 5,670 cubic feet,in all, of the mixture. Hence, the stopcock of my cylinder, when fullyopen, expends 27 cubic feet per hour, with a flame at least six timesas strong as that of the large lamps used for lighting streets. On anaverage, then, and in order to keep myself at a very moderate elevation,I should not burn more than nine cubic feet per hour, so that mytwenty-five gallons of water represent six hundred and thirty-six hoursof aerial navigation, or a little more than twenty-six days.
"Well, as I can descend when I please, to replenish my stock of water onthe way, my trip might be indefinitely prolonged.
"Such, gentlemen, is my secret. It is simple, and, like most simplethings, it cannot fail to succeed. The dilation and contraction of thegas in the balloon is my means of locomotion, which calls for neithercumbersome wings, nor any other mechanical motor. A calorifere toproduce the changes of temperature, and a cylinder to generate the heat,are neither inconvenient nor heavy. I think, therefore, that I havecombined all the ele
ments of success."
Dr. Ferguson here terminated his discourse, and was most heartilyapplauded. There was not an objection to make to it; all had beenforeseen and decided.
"However," said the captain, "the thing may prove dangerous."
"What matters that," replied the doctor, "provided that it bepracticable?"
