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 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 constituent 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 stopcock 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 cumbersome 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 anchored 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 latitudes. 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 passion. 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
