From the Earth to the Moon (9 page)

Barbicane intervened to prevent the discussion from becoming too personal:

“Be calm, my friends. Let’s reason. Our cannon will obviously have to be long enough to take full advantage of the expanding gases behind the shell, but it would be useless to go beyond a certain limit.”

“Naturally,” said the major.

“What rules are followed in such cases? The length of a cannon is usually from twenty to twenty-five times the diameter of its projectile, and it weighs between 235 and 240 times as much.”

“That’s not enough!” J. T. Maston said impetuously.

“I agree. According to that rule, the cannon for a projectile with a diameter of nine feet and a weight of 20,000 pounds would be only 225 feet long and would weigh only 4,800,000 pounds.”

“That’s ridiculous!” said J. T. Maston. “We might as well use a pistol!”

“I think so too,” said Barbicane, “and so I propose that we quadruple that length and make a cannon nine hundred feet long.”

The general and the major raised a few objections, but the proposal, vigorously supported by J. T. Maston, was finally adopted.

“And now,” said the major, “how thick shall we make the walls of the cannon?”

“Six feet,” replied Barbicane.

“You’re not thinking of putting a mass like that on a gun carriage, are you?” asked the major.

“It would be magnificent!” said J. T. Maston.

“But unfeasible,” said Barbicane. “No, I’m thinking of casting the cannon in the ground, reinforcing it with wrought-iron bands, and surrounding it with masonry, so that it will benefit from the resistance of the earth around it. When the barrel has been cast, it will be carefully reamed and measured to avoid the slightest gap between the projectile and the bore. That way, there will be no loss of gas and all the expansive power of the gunpowder will be used for propulsion.”

“Hurrah!” cried J. T. Maston. “We’ve got our cannon!”

“Not yet,” said Barbicane, calming him with his hand.

“Why not?”

“Because we haven’t discussed its shape. Will it be a cannon, a howitzer, or a mortar?”

“A cannon,” said General Morgan.

“A howitzer,” said Major Elphiston.

“A mortar!” said J. T. Maston.

Another argument was about to break out, with each of the three advocating his favorite weapon, when Barbicane cut it short:

“My friends, I’m going to put you all in agreement. Our Columbiad will be all three of those weapons at once. It will be a cannon, since its chamber will have the same diameter as its bore; it will be a howitzer, since it will fire a hollow shell; and it will be a mortar, since it will be elevated at an angle of ninety degrees, and since, set firmly in the earth with no possibility of recoil, it will transmit its full propulsive power to the projectile.”

The three men voiced their approval.

“I’d like to ask one question,” said the major. “Will this cannon-howitzer-mortar have a rifled bore?”

“No,” replied Barbicane. “We’ll need an enormous initial velocity, and, as you know, a smoothbore barrel fires a ball faster than a rifled one.”

“That’s true.”

“Now
we’ve got it!” said J. T. Maston.

“Not quite,” said Barbicane.

“Why not?”

“Because we don’t know what metal it will be made of.”

“Let’s decide right now.”

“That’s what I was about to suggest.”

Each member of the committee downed a dozen sandwiches, followed by a large cup of tea, and the discussion was resumed.

“My friends,” said Barbicane, “our cannon must be extremely tough and hard, infusible, rustproof, and impervious to the corrosive action of acids.”

“There’s no doubt about that,” said the major, “and since we’ll have to use a huge amount of metal, we won’t have a very wide choice.”

“I propose that we use the best alloy discovered so
far,” said the general: “a hundred parts copper, twelve parts tin, and six parts brass.”

“I admit that’s an alloy which has given very good results,” said Barbicane, “but in this case it would be too expensive and hard to use. I think we’ll have to use a cheap but excellent metal such as cast iron. Don’t you agree, Major?”

“Certainly.”

“Cast iron costs only a tenth as much as bronze. It’s easy to melt, it can be simply cast in sand molds, and it can be quickly worked, so it will save us time as well as money. Furthermore, it’s quite good. I remember that during the siege of Atlanta there were cast-iron cannons that fired a thousand shots apiece, at the rate of one every twenty minutes, without suffering any damage.”

“But cast iron is very brittle,” said the general.

“And very strong, too. Our cannon won’t burst, I guarantee you that.”

“A burst barrel is no disgrace,” J. T. Maston said sententiously.

“Of course not,” replied Barbicane. “I’m now going to ask our worthy secretary to calculate the weight of a cast-iron cannon with a length of 900 feet, an inner diameter of nine feet, and walls of six feet thick.”

“Just a moment,” said J. T. Maston.

As he had done the day before, he wrote out his formulas with wondrous ease, and a minute later he announced:

“The cannon will weigh 68,040 tons.”

“And at two cents a pound, how much will it cost?”

“It will cost $2,721,600.”

J. T. Maston, the major, and the general looked at Barbicane with anxiety.

“Well, my friends,” he said, “I’ll repeat what I told
you yesterday: don’t worry, we’ll have no shortage of money!”

After this assurance from the president of the Gun Club, the meeting ended and the committee agreed to meet again the following evening.

T
HE QUESTION
of powder still had to be dealt with. The public was eagerly awaiting this final decision. Now that the respective sizes of the projectile and the cannon had been established, how much gunpowder would be needed to provide the necessary propulsion? That formidable substance, which man had succeeded in bringing under his control, would have to be used in unheard-of amounts.

It is generally known and often repeated that gunpowder was invented in the fourteenth century by a monk named Schwarz, who paid for his great discovery with his life. But it has now been almost certainly proven that this story must be classified as a medieval legend. Gunpowder was invented by no one. It is directly descended from “Greek fire,” which, like it, is composed of sulfur and saltpeter; but in the course of time those deflagrating mixtures were transformed into explosive ones.

But while the learned are perfectly familiar with the false history of gunpowder, few people realize its mechanical power. This must be known in order to understand the importance of the question under consideration by the committee.

A quart of gunpowder weighs about two pounds. When it burns, it produces 400 quarts of gas. When this
gas is released, under the effect of a temperature of 2,400 degrees, it occupies a volume of 4,000 quarts. Thus the ratio between a certain volume of gunpowder and the volume of gas it produces when it burns is 4,000 to one. It is not difficult to imagine the awesome power of that gas when it is confined in a space 4,000 times too small for it.

The members of the committee were well aware of this when they began their third meeting. Barbicane gave the floor to Major Elphiston, who had been in charge of powder production during the war.

“Gentlemen,” said the distinguished chemist, “I’ll begin by giving you some undeniable figures that we can use as a basis for discussion. The twenty-four-pounder, which our honorable secretary spoke about so poetically the day before yesterday, uses only sixteen pounds of powder to fire its ball.”

“Are you sure of that figure?” asked Barbicane.

“Quite sure. The Armstrong cannon uses only seventy-five pounds of powder for its 800-pound projectile, and the Rodman Columbiad uses only 160 pounds of powder to shoot its half-ton projectile a distance of six miles. These facts are incontestable, because I personally gathered them from the reports of the Artillery Committee.”

“That’s perfectly true,” said the general.

“Here’s the conclusion to be drawn from these figures,” said the major: “the quantity of powder doesn’t increase in direct proportion to the weight of the projectile. The twenty-four-pounder uses sixteen pounds of powder, or two-thirds the weight of its projectile, but that ratio isn’t constant.

“If it were, a projectile weighing half a ton would require 667 pounds of powder, but it actually requires only 160 pounds.”

“What point are you trying to make?” asked Barbicane.

“If you carry your theory to its logical conclusion, Major,” said J. T. Maston, “you’ll have to maintain that when the projectile becomes heavy enough, it won’t need any powder at all!”

“You’re playful even in the midst of a serious discussion, Maston,” said the major, “but don’t worry: I’ll soon propose a quantity of powder that will satisfy your honor as an artilleryman. I do want to point out, however, that after experiments made during the war the powder charge for the biggest cannons was reduced to a tenth of the weight of their projectiles.”

“That’s also perfectly true,” said the general. “But before we decide on the amount of powder necessary to propel our projectile, I think we’d better agree on what kind of powder we’ll use.”

“We’ll use coarse-grained powder,” said the major. “It burns faster than fine-grained powder.”

“Yes,” said the general, “but it has a high degree of brisance and eventually damages a gun’s bore.”

“That’s a drawback for a cannon meant for long use, but not for our Columbiad. We’ll run no risk of a burst barrel, and the powder will have to ignite very quickly, so that its energy will be completely utilized.”

“We could make several priming holes,” said J. T. Maston, “and ignite the powder at different places simultaneously.”

“I suppose so,” replied the major, “but that would make the operation more difficult. I’ll stick to my coarse-grained powder because it will eliminate such difficulties.”

“So be it,” said the general.

“In his Columbiad,” said the major, “Rodman used a powder with grains the size of chestnuts, made of willow
charcoal that was simply roasted in iron boilers. It was hard and glossy, left no trace on the hand, contained a high proportion of hydrogen and oxygen, burned instantaneously, and, despite its great brisance, it wasn’t hard on gun barrels.”

“Then I don’t see any reason to hesitate,” said J. T. Maston. “Our choice is clear.”

“Unless you’d prefer gold powder,” said the major, laughing. This earned him a threatening gesture from his touchy friend’s iron hook.

So far Barbicane had remained aloof from the discussion. He had been merely listening and letting the others talk. It was obvious that he had an idea. He contented himself with saying:

“And now, my friends, what quantity of powder do you propose?”

His three colleagues looked at one another for a few moments. Finally the general said, “Two hundred thousand pounds.”

“Five hundred thousand,” said the major.

“Eight hundred thousand pounds!” said J. T. Maston.

This time the major could not accuse him of exaggerating. After all, they were planning to send a 20,000-pound projectile to the moon with an initial velocity of 36,000 feet per second. There was a silence after the three men had made their respective proposals.

It was finally broken by Barbicane:

“Gentlemen,” he said calmly, “I start from the principle that the strength of our cannon, built correctly, will be unlimited. I’m therefore going to surprise Mr. Maston by proposing to double his 800,000 pounds of powder.”

“A million six hundred thousand pounds?” said J. T. Maston, bounding on his chair.

“Yes.”

“But then we’ll have to come back to my half-mile cannon!”

“That’s obvious,” said the major.

“A million six hundred thousand pounds of powder,” said J. T. Maston, “will occupy a volume of about 22,000 cubic feet. Since your cannon has a capacity of only 54,000 cubic feet, it will be half full, and the bore will be so short that the expanding gases won’t be able to give the projectile enough velocity.”

There was no answer to that. J. T. Maston had spoken the truth. They all looked at Barbicane.

“Nevertheless,” he said, “I insist on using that much powder. Think of it: 1,600,000 pounds of powder will produce 2,500,000 cubic feet of gas. Two and a half million! Do you realize what that means?”

“But how can we do it?” asked the general.

“It’s quite simple: we must reduce that enormous mass of powder without diminishing its power.”

“Very well, but how?”

“I’ll tell you,” Barbicane said simply. The others stared at him eagerly. “Nothing could be simpler than to reduce that amount of powder to a quarter of its normal volume. You’re all familiar with that singular substance which forms the elementary tissues of plants and is known as cellulose.”

“Ah, now I understand you!” said the major.

“It can be obtained in a pure state from various sources,” Barbicane went on, “especially cotton, which is the fiber that surrounds the seeds of the cotton plant. When cotton is combined with cold nitric acid, it’s transformed into a substance that’s extremely insoluble, combustible, and explosive. It was discovered over thirty years ago, in 1832, by a French chemist named
Braconnot. He called it
xyloïdine.
In 1838 another Frenchman, Pelouze, studied its various properties, and in 1846 Schönbein, a chemistry professor in Basel, proposed that it be used as gunpowder. That powder is known as guncotton.”