Preliminary trials—The doctor's five containers—The gas

'M ANY ATTEMPTS have been made, gentlemen, to rise and drop at will in a balloon without loss of gas or ballast. A French aeronaut, M. Meunier, proposed to achieve this object by means of compressed air. Dr van Hecke, a Belgian, using planes and paddles, developed a vertical force which in most cases would have been inadequate. The practical results obtained by these methods were negligible.

'I therefore made up my mind to approach the question more directly. To begin with, I do away entirely with ballast, except for emergencies, such as the breakdown of my apparatus or the need to rise instantly in order to avoid some unexpected obstacle.

'My method of rising and descending consists merely in expanding or contracting the gas contained in the envelope of the balloon by changing the temperature; and this is how I do it.

'You saw me bring on board with the car several containers the purpose of which was unknown to you. There are five of them. The first contains about twenty-five gallons of water, to which I add a few drops of sulphuric acid to increase its conductivity. I then decompose it by means of a powerful Bunsen battery. Water, as you know, is made up of two parts hydrogen and one part oxygen. Separated by the battery, the oxygen is collected from its positive pole in a second container, while a third, fitted above the second and of double its capacity, takes the hydrogen coming from the negative pole.

'These two containers are connected with a fourth by means of taps, the bore of one of which is double that of the other. This container is called the mixing chamber, for it is there that the two gases, separated by the decomposition of the water, mix. The capacity of this chamber is about fortyone cubic feet, and the upper part is fitted with a platinum tube to which a tap is fixed. You will realise, gentlemen, that the apparatus I am describing to you is purely and simply an oxyhydrogen burner, the temperature of which is greater than that of a blacksmith's forge.

'That being clear, I will pass on to the second part of the apparatus. From the lower part of my balloon, which is hermetically closed, project two tubes a little distance apart. One begins in the middle of the upper layers of the hydrogen, the other among the lower. At intervals these two tubes are fitted with strong rubber joints which allow them to give to the swaying of the balloon. They both reach as far as the car where they enter a cylindrical chamber which is called the heating chamber, and is closed at its two extremities by strong discs. The pipe from the lower part of the balloon enters this cylinder through the lower disc, after which it becomes a spiral, the coil stretching to the full height of the cylinder. Before emerging again, this spiral passes through a small cone the convex base of which, shaped like a skull-cap, bulges downwards. To the apex of this cone is fitted the second pipe, which, as I have explained, connects with the lower part of the balloon.

'The convex base of the cone is of platinum to prevent its melting under the action of the heating chamber, which is situated at the bottom of the iron case, inside the spiral, so that the flame just touches the base of the cone.

'You know, gentlemen, the principle of a furnace for the central heating of a house. You know how it works. The air of the rooms is forced through the pipes and returned at a higher temperature. What I have just described to you is nothing more or less than a central heating furnace.

'Now, what actually happens? When the heating apparatus is lit, the hydrogen in the spiral and convex cone is heated and rises rapidly through the pipe leading to the upper part of the balloon. A vacuum is formed below which draws down the gas from the lower parts. This, in its turn, is heated and is constantly being replaced. In this way a very rapid flow of gas takes place through the pipes and spiral, the gas being continually drawn from the balloon and returning to it after being heated.

'Now gases expand 1/480 of their volume per degree of temperature. If, therefore, I increase the temperature by 18 degrees, the volume of the hydrogen in the balloon will be increased 1/480 or 1674 cubic feet. It will thus displace 1674 additional cubic feet of air, and this will increase its lifting force by 130 lbs. This, then, is tantamount to throwing out the same weight of ballast. If I increase the temperature by 180 degrees, the gas will increase in volume 1/480, will displace 16,740 additional cubic feet, and the lifting force will increase by 1300 lbs.

'You see, gentlemen, I can easily obtain considerable variations in the conditions of equilibrium. The volume of the balloon has been so calculated that when it is half-inflated it will displace a weight of air exactly equal to that of the envelope, the hydrogen and the car together with all its passengers and accessories. Up to this point of inflation it is in exact equilibrium in the air, neither rising nor dropping.

'To rise, I raise the gas to a temperature higher than that of the surrounding air by means of my burner, obtaining a greater pressure and increasing the dilation of the balloon, which rises in proportion as I expand the hydrogen. Coming down is, of course, effected by diminishing the heat of the furnace and lowering the temperature. Rising, therefore, will generally be much more rapid than descending, but that is an advantage, as I shall never need to come down rapidly, whereas a quick ascent will be necessary to clear obstacles. The dangers are below, not above.

'Moreover, as I have already told you, I am taking a certain amount of ballast, which will allow me to rise even quicker still, should that prove necessary. My emission pipe, situated near the top of the balloon, becomes nothing more than a safety-valve. The balloon always retains its full charge of hydrogen, and the variations of temperature that I bring about in the enclosed gas are of themselves sufficient to allow me to rise or drop.

'There's just one thing, gentlemen, that I should like to add as a practical detail. The combustion of hydrogen and oxygen at the top of the furnace produces only steam. I have therefore fitted the lower part of the iron cylinder with an escape-valve functioning at less than two atmospheres'pressure. Consequently, as soon as the steam develops this pressure, it is automatically released.

'And now for some exact figures. 25 gallons of water decomposed into its constituent elements give 222 lbs of oxygen and 28 lbs of hydrogen. This represents, at atmospheric pressure, 2050 cubic feet of oxygen and 4100 cubic feet of hydrogen, making 6150 cubic feet of the mixture. The tap of my furnace when fully open can pass 27 cubic feet an hour, with a flame at least six times as strong as that of a large street lamp. On an average, then, to maintain an ordinary altitude, I shall not burn more than 9 cubic feet per hour. My 25 gallons of water therefore represent for me 683 hours of travel in the air, or rather more than 26 days. But, as I can come down when I like and replenish my supply of water on the way, my journey could be prolonged indefinitely.

'That is my secret, gentlemen. It is simple and, like all simple things, cannot fail to succeed. Expansion and contraction of the gas in the balloon; such is my method, and it involves no cumbersome planes or engines. A furnace to produce the changes of temperature, a chamber to heat the gas: these are neither cumbersome nor heavy. I think, then, that I have provided myself with all the essential conditions for success.'

With these words Dr Fergusson brought his discourse to a conclusion and was heartily applauded. There were no objections to his scheme. Everything had been foreseen and solved.

'All the same,' said the captain, 'it may be dangerous.'

'And what if it is?' the doctor answered quietly. 'So long as it's practicable.' B4dj+iyALjr5KEp7MYOOaSfXsiq0VWAh+Qp+dGpGvVmYVt+rRn/EZv1uR0V5/PBP