It seems that we are to sail for the moon."

"You mean the Mountains of the Moon, which are not quite so far off. But, never mind, one trip is just as dangerous as the other!"

"Dangerous! What! with a man like Dr. Ferguson?"

"I don't want to spoil your illusions, my good Joe; but this undertaking of his is nothing more nor less than the act of a madman. He won't go, though!"

"He won't go, eh? Then you haven't seen his balloon at Mitchell's factory in the Borough?"

"I'll take precious good care to keep away from it!"

"Well, you'll lose a fine sight, sir. What a splendid thing it is! What a pretty shape! What a nice car! How snug we'll feel in it!"

"Then you really think of going with your master?"

"I?" answered Joe, with an accent of profound conviction. "Why, I'd go with him wherever he pleases! Who ever heard of such a thing? Leave him to go off alone, after we've been all over the world together! Who would help him, when he was tired? Who would give him a hand in climbing over the rocks? Who would attend him when he was sick? No, Mr. Kennedy, Joe will always stick to the doctor!"

"You're a fine fellow, Joe!"

"But, then, you're coming with us!"

"Oh! certainly," said Kennedy; "that is to say, I will go with you up to the last moment, to prevent Samuel even then from being guilty of such an act of folly! I will follow him as far as Zanzibar, so as to stop him there, if possible."

"You'll stop nothing at all, Mr. Kennedy, with all respect to you, sir. My master is no hare-brained person; he takes a long time to think over what he means to do, and then, when he once gets started, the Evil One himself couldn't make him give it up."

"Well, we'll see about that."

"Don't flatter yourself, sir—but then, the main thing is, to have you with us. For a hunter like you, sir, Africa's a great country. So, either way, you won't be sorry for the trip."

"No, that's a fact, I shan't be sorry for it, if I can get this crazy man to give up his scheme."

"By-the-way," said Joe, "you know that the weighing comes off to-day."

"The weighing—what weighing?"

"Why, my master, and you, and I, are all to be weighed to-day!"

"What! like horse-jockeys?"

"Yes, like jockeys. Only, never fear, you won't be expected to make yourself lean, if you're found to be heavy. You'll go as you are."

"Well, I can tell you, I am not going to let myself be weighed," said Kennedy, firmly.

"But, sir, it seems that the doctor's machine requires it."

"Well, his machine will have to do without it."

"Humph! and suppose that it couldn't go up, then?"

"Egad! that's all I want!"

"Come! come, Mr. Kennedy! My master will be sending for us directly."

"I shan't go."

"Oh! now, you won't vex the doctor in that way!"

"Aye! that I will."

"Well!" said Joe with a laugh, "you say that because he's not here; but when he says to your face, 'Dick!' (with all respect to you, sir,) 'Dick, I want to know exactly how much you weigh,' you'll go, I warrant it."

"No, I will NOT go!"

At this moment the doctor entered his study, where this discussion had been taking place; and, as he came in, cast a glance at Kennedy, who did not feel altogether at his ease.

"Dick," said the doctor, "come with Joe; I want to know how much you both weigh."

"But—"

"You may keep your hat on. Come!" And Kennedy went.

They repaired in company to the workshop of the Messrs. Mitchell, where one of those so-called "Roman" scales was in readiness. It was necessary, by the way, for the doctor to know the weight of his companions, so as to fix the equilibrium of his balloon; so he made Dick get up on the platform of the scales. The latter, without making any resistance, said, in an undertone:

"Oh! well, that doesn't bind me to any thing."

"One hundred and fifty-three pounds," said the doctor, noting it down on his tablets.

"Am I too heavy?"

"Why, no, Mr. Kennedy!" said Joe; "and then, you know, I am light to make up for it."

So saying, Joe, with enthusiasm, took his place on the scales, and very nearly upset them in his ready haste. He struck the attitude of Wellington where he is made to ape Achilles, at Hyde-Park entrance, and was superb in it, without the shield.

"One hundred and twenty pounds," wrote the doctor.

"Ah! ha!" said Joe, with a smile of satisfaction
And why did he smile? He never could tell himself.

"It's my turn now," said Ferguson—and he put down one hundred and thirty-five pounds to his own account.

"All three of us," said he, "do not weigh much more than four hundred pounds."

"But, sir," said Joe, "if it was necessary for your expedition, I could make myself thinner by twenty pounds, by not eating so much."

"Useless, my boy!" replied the doctor. "You may eat as much as you like, and here's half-a-crown to buy you the ballast."

CHAPTER SEVENTH.

Geometrical Details.—Calculation of the Capacity of the Balloon.—The
Double Receptacle.—The Covering.—The Car.—The Mysterious Apparatus.
—The Provisions and Stores.—The Final Summing up.

Dr. Ferguson had long been engaged upon the details of his expedition. It is easy to comprehend that the balloon —that marvellous vehicle which was to convey him through the air—was the constant object of his solicitude.

At the outset, in order not to give the balloon too ponderous dimensions, he had decided to fill it with hydrogen gas, which is fourteen and a half times lighter than common air. The production of this gas is easy, and it has given the greatest satisfaction hitherto in aerostatic experiments.

The doctor, according to very accurate calculations, found that, including the articles indispensable to his journey and his apparatus, he should have to carry a weight of 4,000 pounds; therefore he had to find out what would be the ascensional force of a balloon capable of raising such a weight, and, consequently, what would be its capacity.

A weight of four thousand pounds is represented by a displacement of the air amounting to forty-four thousand eight hundred and forty-seven cubic feet; or, in other words, forty-four thousand eight hundred and forty-seven cubic feet of air weigh about four thousand pounds.

By giving the balloon these cubic dimensions, and filling it with hydrogen gas, instead of common air—the former being fourteen and a half times lighter and weighing therefore only two hundred and seventy-six pounds—a difference of three thousand seven hundred and twenty-four pounds in equilibrium is produced; and it is this difference between the weight of the gas contained in the balloon and the weight of the surrounding atmosphere that constitutes the ascensional force of the former.

However, were the forty-four thousand eight hundred and forty-seven cubic feet of gas of which we speak, all introduced into the balloon, it would be entirely filled; but that would not do, because, as the balloon continued to mount into the more rarefied layers of the atmosphere, the gas within would dilate, and soon burst the cover containing it. Balloons, then, are usually only two-thirds filled.

But the doctor, in carrying out a project known only to himself, resolved to fill his balloon only one-half; and, since he had to carry forty-four thousand eight hundred and forty-seven cubic feet of gas, to give his balloon nearly double capacity he arranged it in that elongated, oval shape which has come to be preferred. The horizontal diameter was fifty feet, and the vertical diameter seventy-five feet. He thus obtained a spheroid, the capacity of which amounted, in round numbers, to ninety thousand cubic feet.

Could Dr. Ferguson have used two balloons, his chances of success would have been increased; for, should one burst in the air, he could, by throwing out ballast, keep himself up with the other. But the management of two balloons would, necessarily, be very difficult, in view of the problem how to keep them both at an equal ascensional force.

After having pondered the matter carefully, Dr. Ferguson, by an ingenious arrangement, combined the advantages of two balloons, without incurring their inconveniences. He constructed two of different sizes, and inclosed the smaller in the larger one. His external balloon, which had the dimensions given above, contained a less one of the same shape, which was only forty-five feet in horizontal, and sixty-eight feet in vertical diameter.