“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 anything.”
“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.”
VII
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 enclosed 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. The capacity of this interior balloon was only sixty-seven thousand cubic feet: it was to float in the fluid surrounding it. A valve opened from one balloon into the other, and thus enabled the aeronaut to communicate with both.
This arrangement offered the advantage, that if gas had to be let off, so as to descend, that which was in the outer balloon would go first; and, were it completely emptied, the smaller one would still remain intact. The outer envelope might then be cast off as a useless encumbrance; and the second balloon, left free to itself, would not offer the
