"You all know, gentlemen, what a calorifere, to heat apartments, is. You know how it acts. The air of the apartments is forced to pa.s.s through its pipes, and is then released with a heightened temperature. Well, what I have just described to you is nothing more nor less than a calorifere.

"In fact, what is it that takes place? The cylinder once lighted, the hydrogen in the spiral and in the concave cone becomes heated, and rapidly ascends through the pipe that leads to the upper part of the balloon. A vacuum is created below, and it attracts the gas in the lower parts; this becomes heated in its turn, and is continually replaced; thus, an extremely rapid current of gas is established in the pipes and in the spiral, which issues from the balloon and then returns to it, and is heated over again, incessantly.

"Now, the cases increase 1/480 of their volume for each degree of heat applied. If, then, I force the temperature 18 degrees, the hydrogen of the balloon will dilate 18/480 or 1614 cubic feet, and will, therefore, displace 1614 more cubic feet of air, which will increase its ascensional power by 160 pounds. This is equivalent to throwing out that weight of ballast. If I augment the temperature by 180 degrees, the gas will dilate 180/480 and will displace 16,740 cubic feet more, and its ascensional force will be augmented by 1,600 pounds.

"Thus, you see, gentlemen, that I can easily effect very considerable changes of equilibrium. The volume of the balloon has been calculated in such manner that, when half inflated, it displaces a weight of air exactly equal to that of the envelope containing the hydrogen gas, and of the car occupied by the pa.s.sengers, and all its apparatus and accessories. At this point of inflation, it is in exact equilibrium with the air, and neither mounts nor descends.

"In order, then, to effect an ascent, I give the gas a temperature superior to the temperature of the surrounding air by means of my cylinder. By this excess of heat it obtains a larger distention, and inflates the balloon more. The latter, then, ascends in proportion as I heat the hydrogen.

"The descent, of course, is effected by lowering the heat of the cylinder, and letting the temperature abate. The ascent would be, usually, more rapid than the descent; but that is a fortunate circ.u.mstance, 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 avoid obstacles. The real danger lurks below, and not above.

"Besides, as I have said, I have a certain quant.i.ty of ballast, which will 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 quant.i.ty of hydrogen, and the variations of temperature that I produce in the midst of this shut-up gas are, of themselves, sufficient to provide for all these ascending and 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 the cylinder 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 steam escapes of itself.

"Here are the exact figures: 25 gallons of water, separated into its const.i.tuent elements, yield 200 pounds of oxygen and 25 pounds of hydrogen. This represents, at atmospheric tension, 1,800 cubic feet of the former and 3,780 cubic feet of the latter, or 5,670 cubic feet, in all, of the mixture. Hence, the stopc.o.c.k of my cylinder, when fully open, expends 27 cubic feet per hour, with a flame at least six times as strong as that of the large lamps used for lighting streets. On an average, 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 my twenty-five gallons of water represent six hundred and thirty-six hours of aerial navigation, or a little more than twenty-six days.

"Well, as I can descend when I please, to replenish my stock of water on the way, my trip might be indefinitely prolonged.

"Such, gentlemen, is my secret. It is simple, and, like most simple things, it cannot fail to succeed. The dilation and contraction of the gas in the balloon is my means of locomotion, which calls for neither c.u.mbersome wings, nor any other mechanical motor. A calorifere to produce the changes of temperature, and a cylinder to generate the heat, are neither inconvenient nor heavy. I think, therefore, that I have combined all the elements of success."

Dr. Ferguson here terminated his discourse, and was most heartily applauded. There was not an objection to make to it; all had been foreseen and decided.

"However," said the captain, "the thing may prove dangerous."

"What matters that," replied the doctor, "provided that it be practicable?"

CHAPTER ELEVENTH.

The Arrival at Zanzibar.-The English Consul.-Ill-will of the Inhabitants.-The Island of Koumbeni.-The Rain-Makers.-Inflation of the Balloon.-Departure on the 18th of April.-The last Good-by.-The Victoria.

An invariably favorable wind had accelerated the progress of the Resolute toward the place of her destination. The navigation of the Mozambique Channel was especially calm and pleasant. The agreeable character of the trip by sea was regarded as a good omen of the probable issue of the trip through the air. Every one looked forward to the hour of arrival, and sought to give the last touch to the doctor's preparations.

At length the vessel hove in sight of the town of Zanzibar, upon the island of the same name, and, on the 15th of April, at 11 o'clock in the morning, she anch.o.r.ed in the port.

The island of Zanzibar belongs to the Imaum of Muscat, an ally of France and England, and is, undoubtedly, his finest settlement. The port is frequented by a great many vessels from the neighboring countries.

The island is separated from the African coast only by a channel, the greatest width of which is but thirty miles.

It has a large trade in gums, ivory, and, above all, in "ebony," for Zanzibar is the great slave-market. Thither converges all the booty captured in the battles which the chiefs of the interior are continually fighting. This traffic extends along the whole eastern coast, and as far as the Nile lat.i.tudes. Mr. G. Lejean even reports that he has seen it carried on, openly, under the French flag.

Upon the arrival of the Resolute, the English consul at Zanzibar came on board to offer his services to the doctor, of whose projects the European newspapers had made him aware for a month past. But, up to that moment, he had remained with the numerous phalanx of the incredulous.

"I doubted," said he, holding out his hand to Dr. Ferguson, "but now I doubt no longer."

He invited the doctor, Kennedy, and the faithful Joe, of course, to his own dwelling. Through his courtesy, the doctor was enabled to have knowledge of the various letters that he had received from Captain Speke. The captain and his companions had suffered dreadfully from hunger and bad weather before reaching the Ugogo country. They could advance only with extreme difficulty, and did not expect to be able to communicate again for a long time.

"Those are perils and privations which we shall manage to avoid," said the doctor.

The baggage of the three travellers was conveyed to the consul's residence. Arrangements were made for disembarking the balloon upon the beach at Zanzibar. There was a convenient spot, near the signal-mast, close by an immense building, that would serve to shelter it from the east winds. This huge tower, resembling a tun standing on one end, beside which the famous Heidelberg tun would have seemed but a very ordinary barrel, served as a fortification, and on its platform were stationed Belootchees, armed with lances. These Belootchees are a kind of brawling, good-for-nothing Janizaries.

But, when about to land the balloon, the consul was informed that the population of the island would oppose their doing so by force. Nothing is so blind as fanatical pa.s.sion. The news of the arrival of a Christian, who was to ascend into the air, was received with rage. The negroes, more exasperated than the Arabs, saw in this project an attack upon their religion. They took it into their heads that some mischief was meant to the sun and the moon. Now, these two luminaries are objects of veneration to the African tribes, and they determined to oppose so sacrilegious an enterprise.

The consul, informed of their intentions, conferred with Dr. Ferguson and Captain Bennet on the subject. The latter was unwilling to yield to threats, but his friend dissuaded him from any idea of violent retaliation.

"We shall certainly come out winners," he said. "Even the imaum's soldiers will lend us a hand, if we need it. But, my dear captain, an accident may happen in a moment, and it would require but one unlucky blow to do the balloon an irreparable injury, so that the trip would be totally defeated; therefore we must act with the greatest caution."

"But what are we to do? If we land on the coast of Africa, we shall encounter the same difficulties. What are we to do?"

"Nothing is more simple," replied the consul. "You observe those small islands outside of the port; land your balloon on one of them; surround it with a guard of sailors, and you will have no risk to run."

"Just the thing!" said the doctor, "and we shall be entirely at our ease in completing our preparations."

The captain yielded to these suggestions, and the Resolute was headed for the island of Koumbeni. During the morning of the 16th April, the balloon was placed in safety in the middle of a clearing in the great woods, with which the soil is studded.

Two masts, eighty feet in height, were raised at the same distance from each other. Blocks and tackle, placed at their extremities, afforded the means of elevating the balloon, by the aid of a transverse rope. It was then entirely uninflated. The interior balloon was fastened to the exterior one, in such manner as to be lifted up in the same way. To the lower end of each balloon were fixed the pipes that served to introduce the hydrogen gas.

The whole day, on the 17th, was spent in arranging the apparatus destined to produce the gas; it consisted of some thirty casks, in which the decomposition of water was effected by means of iron-filings and sulphuric acid placed together in a large quant.i.ty of the first-named fluid. The hydrogen pa.s.sed into a huge central cask, after having been washed on the way, and thence into each balloon by the conduit-pipes. In this manner each of them received a certain accurately-ascertained quant.i.ty of gas. For this purpose, there had to be employed eighteen hundred and sixty-six pounds of sulphuric acid, sixteen thousand and fifty pounds of iron, and nine thousand one hundred and sixty-six gallons of water. This operation commenced on the following night, about three A.M., and lasted nearly eight hours. The next day, the balloon, covered with its network, undulated gracefully above its car, which was held to the ground by numerous sacks of earth. The inflating apparatus was put together with extreme care, and the pipes issuing from the balloon were securely fitted to the cylindrical case.

The anchors, the cordage, the instruments, the travelling-wraps, the awning, the provisions, and the arms, were put in the place a.s.signed to them in the car. The supply of water was procured at Zanzibar. The two hundred pounds of ballast were distributed in fifty bags placed at the bottom of the car, but within arm's-reach.

These preparations were concluded about five o'clock in the evening, while sentinels kept close watch around the island, and the boats of the Resolute patrolled the channel.

The blacks continued to show their displeasure by grimaces and contortions. Their obi-men, or wizards, went up and down among the angry throngs, pouring fuel on the flame of their fanaticism; and some of the excited wretches, more furious and daring than the rest, attempted to get to the island by swimming, but they were easily driven off.

Thereupon the sorceries and incantations commenced; the "rain-makers," who pretend to have control over the clouds, invoked the storms and the "stone-showers," as the blacks call hail, to their aid. To compel them to do so, they plucked leaves of all the different trees that grow in that country, and boiled them over a slow fire, while, at the same time, a sheep was killed by thrusting a long needle into its heart. But, in spite of all their ceremonies, the sky remained clear and beautiful, and they profited nothing by their slaughtered sheep and their ugly grimaces.

The blacks then abandoned themselves to the most furious orgies, and got fearfully drunk on "tembo," a kind of ardent spirits drawn from the cocoa-nut tree, and an extremely heady sort of beer called "togwa." Their chants, which were dest.i.tute of all melody, but were sung in excellent time, continued until far into the night.

About six o'clock in the evening, the captain a.s.sembled the travellers and the officers of the ship at a farewell repast in his cabin. Kennedy, whom n.o.body ventured to question now, sat with his eyes riveted on Dr. Ferguson, murmuring indistinguishable words. In other respects, the dinner was a gloomy one. The approach of the final moment filled everybody with the most serious reflections. What had fate in store for these daring adventurers? Should they ever again find themselves in the midst of their friends, or seated at the domestic hearth? Were their travelling apparatus to fail, what would become of them, among those ferocious savage tribes, in regions that had never been explored, and in the midst of boundless deserts?

Such thoughts as these, which had been dim and vague until then, or but slightly regarded when they came up, returned upon their excited fancies with intense force at this parting moment. Dr. Ferguson, still cold and impa.s.sible, talked of this, that, and the other; but he strove in vain to overcome this infectious gloominess. He utterly failed.

As some demonstration against the personal safety of the doctor and his companions was feared, all three slept that night on board the Resolute. At six o'clock in the morning they left their cabin, and landed on the island of Koumbeni.

The balloon was swaying gently to and fro in the morning breeze; the sand-bags that had held it down were now replaced by some twenty strong-armed sailors, and Captain Bennet and his officers were present to witness the solemn departure of their friends.

At this moment Kennedy went right up to the doctor, grasped his hand, and said: "Samuel, have you absolutely determined to go?"

"Solemnly determined, my dear d.i.c.k."

"I have done every thing that I could to prevent this expedition, have I not?"

"Every thing!"

"Well, then, my conscience is clear on that score, and I will go with you."

"I was sure you would!" said the doctor, betraying in his features swift traces of emotion.

At last the moment of final leave-taking arrived. The captain and his officers embraced their dauntless friends with great feeling, not excepting even Joe, who, worthy fellow, was as proud and happy as a prince. Every one in the party insisted upon having a final shake of the doctor's hand.

At nine o'clock the three travellers got into their car. The doctor lit the combustible in his cylinder and turned the flame so as to produce a rapid heat, and the balloon, which had rested on the ground in perfect equipoise, began to rise in a few minutes, so that the seamen had to slacken the ropes they held it by. The car then rose about twenty feet above their heads.

"My friends!" exclaimed the doctor, standing up between his two companions, and taking off his hat, "let us give our aerial ship a name that will bring her good luck! let us christen her Victoria!"

This speech was answered with stentorian cheers of "Huzza for the Queen! Huzza for Old England!"

At this moment the ascensional force of the balloon increased prodigiously, and Ferguson, Kennedy, and Joe, waved a last good-by to their friends.

"Let go all!" shouted the doctor, and at the word the Victoria shot rapidly up into the sky, while the four carronades on board the Resolute thundered forth a parting salute in her honor.

CHAPTER TWELFTH

Crossing the Strait.-The Mrima.-d.i.c.k's Remark and Joe's Proposition.-A Recipe for Coffee-making.-The Uzaramo.-The Unfortunate Maizan.-Mount Dathumi.-The Doctor's Cards.-Night under a Nopal.

The air was pure, the wind moderate, and the balloon ascended almost perpendicularly to a height of fifteen hundred feet, as indicated by a depression of two inches in the barometric column.

At this height a more decided current carried the balloon toward the southwest. What a magnificent spectacle was then outspread beneath the gaze of the travellers! The island of Zanzibar could be seen in its entire extent, marked out by its deeper color upon a vast planisphere; the fields had the appearance of patterns of different colors, and thick clumps of green indicated the groves and thickets.

The inhabitants of the island looked no larger than insects. The huzzaing and shouting were little by little lost in the distance, and only the discharge of the ship's guns could be heard in the concavity beneath the balloon, as the latter sped on its flight.

"How fine that is!" said Joe, breaking silence for the first time.

He got no reply. The doctor was busy observing the variations of the barometer and noting down the details of his ascent.

Kennedy looked on, and had not eyes enough to take in all that he saw.

The rays of the sun coming to the aid of the heating cylinder, the tension of the gas increased, and the Victoria attained the height of twenty-five hundred feet.

The Resolute looked like a mere c.o.c.kle-sh.e.l.l, and the African coast could be distinctly seen in the west marked out by a fringe of foam.

"You don't talk?" said Joe, again.

"We are looking!" said the doctor, directing his spy-gla.s.s toward the mainland.

"For my part, I must talk!"

"As much as you please, Joe; talk as much as you like!"

And Joe went on alone with a tremendous volley of exclamations. The "ohs!" and the "ahs!" exploded one after the other, incessantly, from his lips.

During his pa.s.sage over the sea the doctor deemed it best to keep at his present elevation. He could thus reconnoitre a greater stretch of the coast. The thermometer and the barometer, hanging up inside of the half-opened awning, were always within sight, and a second barometer suspended outside was to serve during the night watches.

At the end of about two hours the Victoria, driven along at a speed of a little more than eight miles, very visibly neared the coast of the mainland. The doctor, thereupon, determined to descend a little nearer to the ground. So he moderated the flame of his cylinder, and the balloon, in a few moments, had descended to an alt.i.tude only three hundred feet above the soil.

It was then found to be pa.s.sing just over the Mrima country, the name of this part of the eastern coast of Africa. Dense borders of mango-trees protected its margin, and the ebb-tide disclosed to view their thick roots, chafed and gnawed by the teeth of the Indian Ocean. The sands which, at an earlier period, formed the coast-line, rounded away along the distant horizon, and Mount Nguru reared aloft its sharp summit in the northwest.

The Victoria pa.s.sed near to a village which the doctor found marked upon his chart as Kaole. Its entire population had a.s.sembled in crowds, and were yelling with anger and fear, at the same time vainly directing their arrows against this monster of the air that swept along so majestically away above all their powerless fury.

The wind was setting to the southward, but the doctor felt no concern on that score, since it enabled him the better to follow the route traced by Captains Burton and Speke.

Kennedy had, at length, become as talkative as Joe, and the two kept up a continual interchange of admiring interjections and exclamations.

"Out upon stage-coaches!" said one.

"Steamers indeed!" said the other.

"Railroads! eh? rubbish!" put in Kennedy, "that you travel on, without seeing the country!"

"Balloons! they're the sort for me!" Joe would add. "Why, you don't feel yourself going, and Nature takes the trouble to spread herself out before one's eyes!"

"What a splendid sight! What a spectacle! What a delight! a dream in a hammock!"

"Suppose we take our breakfast?" was Joe's unpoetical change of tune, at last, for the keen, open air had mightily sharpened his appet.i.te.

"Good idea, my boy!"

"Oh! it won't take us long to do the cooking-biscuit and potted meat?"

"And as much coffee as you like," said the doctor. "I give you leave to borrow a little heat from my cylinder. There's enough and to spare, for that matter, and so we shall avoid the risk of a conflagration."

"That would be a dreadful misfortune!" e.j.a.c.u.l.a.t.ed Kennedy. "It's the same as a powder-magazine suspended over our heads."

"Not precisely," said Ferguson, "but still if the gas were to take fire it would burn up gradually, and we should settle down on the ground, which would be disagreeable; but never fear-our balloon is hermetically sealed."

"Let us eat a bite, then," replied Kennedy.

"Now, gentlemen," put in Joe, "while doing the same as you, I'm going to get you up a cup of coffee that I think you'll have something to say about."