if it be solid, but not if it be hollow,” said Barbicane.
“Hollow!—then it will be an obus?”
“In which we can put despatches,” replied J.T. Maston, “and specimens of our terrestrial productions.”
“Yes, an obus,” answered Barbicane; “that is what it must be; a solid bullet of 108 inches would weigh more than 200,000 lbs., a weight evidently too great; however, as it is necessary to give the projectile a certain stability, I propose to give it a weight of 20,000 lbs.”
“What will be the thickness of the metal?” asked the major.
“If we follow the usual proportions,” replied Morgan, “a diameter of 800 inches demands sides two feet thick at least.”
“That would be much too thick,” answered Barbicane; “we do not want a projectile to pierce armour-plate; it only needs sides strong enough to resist the pressure of the powder-gas. This, therefore, is the problem:—What thickness ought an iron obus to have in order to weigh only 20,000 lbs.? Our clever calculator, Mr. Maston, will tell us at once.”
“Nothing is easier,” replied the honourable secretary.
So saying, he traced some algebraical signs on the paper, amongst which n^2 and x^2 frequently appeared. He even seemed to extract from them a certain cubic root, and said—
“The sides must be hardly two inches thick.”
“Will that be sufficient?” asked the major doubtfully.
“No,” answered the president, “certainly not.”
“Then what must be done?” resumed Elphinstone, looking puzzled.
“We must use another metal instead of cast-iron.”
“Brass?” suggested Morgan.
“No; that is too heavy too, and I have something better than that to propose.”
“What?” asked the major.
“Aluminium,” answered Barbicane.
“Aluminium!” cried all the three colleagues of the president.
“Certainly, my friends. You know that an illustrious French chemist, Henry St. Claire Deville, succeeded in 1854 in obtaining aluminium in a compact mass. This precious metal possesses the whiteness of silver, the indestructibility of gold, the tenacity of iron, the fusibility of copper, the lightness of glass; it is easily wrought, and is very widely distributed in nature, as aluminium forms the basis of most rocks; it is three times lighter than iron, and seems to have been created expressly to furnish us with the material for our projectile!”
“Hurrah for aluminium!” cried the secretary, always very noisy in his moments of enthusiasm.
“But, my dear president,” said the major, “is not aluminium quoted exceedingly high?”
“It was so,” answered Barbicane; “when first discovered a pound of aluminium cost 260 to 280 dollars; then it fell to twenty-seven dollars, and now it is worth nine dollars.”
“But nine dollars a pound,” replied the major, who did not easily give in; “that is still an enormous price.”
“Doubtless, my dear major; but not out of reach.”
“What will the projectile weigh, then?” asked Morgan.
“Here is the result of my calculations,” answered Barbicane. “A projectile of 108 inches in diameter and 12 inches thick would weigh, if it were made of cast-iron, 67,440 lbs.; cast in aluminium it would be reduced to 19,250 lbs.”
“Perfect!” cried Maston; “that suits our programme capitally.”
“Yes,” replied the major; “but do you not know that at nine dollars a pound the projectile would cost—”
“One hundred seventy-three thousand and fifty dollars. Yes, I know that; but fear nothing, my friends; money for our enterprise will not be wanting, I answer for that.”
“It will be showered upon us,” replied J.T. Maston.
“Well, what do you say to aluminium?” asked the president.
“Adopted,” answered the three members of the committee.
“As to the form of the projectile,” resumed Barbicane, “it is of little consequence, since, once the atmosphere cleared, it will find itself in empty space; I therefore propose a round ball, which will turn on itself, if it so pleases.”
Thus ended the first committee meeting. The question of the projectile was definitely resolved upon, and J.T. Maston was delighted with the idea of sending an aluminium bullet to the Selenites, “as it will give them no end of an idea of the inhabitants of the earth!”
Chapter VIII.
History of the Cannon.
The resolutions passed at this meeting produced a great effect outside. Some timid people grew alarmed at the idea of a projectile weighing 20,000 lbs. hurled into space. People asked what cannon could ever transmit an initial speed sufficient for such a mass. The report of the second meeting was destined to answer these questions victoriously.
The next evening the four members of the Gun Club sat down before fresh mountains of sandwiches and a veritable ocean of tea. The debate then began.
“My dear colleagues,” said Barbicane, “we are going to occupy ourselves with the construction of the engine, its length, form, composition, and weight. It is probable that we shall have to give it gigantic dimensions, but, however great our difficulties might be, our industrial genius will easily overcome them. Will you please listen to me and spare objections for the present? I do not fear them.”
An approving murmur greeted this declaration.
“We must not forget,” resumed Barbicane, “to what point our yesterday’s debate brought us; the problem is now the following: how to give an initial speed of 12,000 yards a second to a shot 108 inches in diameter weighing 20,000 lbs.
“That is the problem indeed,” answered Major Elphinstone.
“When a projectile is hurled into space,” resumed Barbicane, “what happens? It is acted upon by three independent forces, the resistance of the medium, the attraction of the earth, and the force of impulsion with which it is animated. Let us examine these three forces. The resistance of the medium—that is to say, the resistance of the air—is of little importance. In fact, the terrestrial atmosphere is only forty miles deep. With a rapidity of 12,000 yards the projectile will cross that in five seconds, and this time will be short enough to make the resistance of the medium insignificant. Let us now pass to the attraction of the earth—that is to say, to the weight of the projectile. We know that that weight diminishes in an inverse ratio to the square of distances—in fact, this is what physics teach us: when a body left to itself falls
