Free From the Earth to the Moon by Jules Verne

happens? It’s acted on by three independent forces: air resistance, the pull of the earth’s gravity, and the propulsive force that’s been applied to it. Let’s examine these three forces. Air resistance will be unimportant. The earth’s atmosphere is only forty miles thick. At a speed of 36,000 feet per second, the shell will go through it in five seconds, and that time is so short that we can regard air resistance as insignificant. Next, let’s consider the pull of the earth’s gravity, in other words the shell’s weight. We know that its weight will diminish in inverse ratio to the square of its distance from the earth. Here’s what physics tells us: when a body is dropped near the surface of the earth, it falls fifteen feet in the first second, but if it were as far away from the earth as the moon is—257,542 miles—it would fall only a twentieth of an inch in the first second; in short, it would remain almost motionless. So we must progressively conquer the force of gravity. How will we do it? By the propulsive force we’ll use.”
    “That’s the difficulty,” said the major.
    “Yes, it is, but we’ll overcome it, because the propulsive force we need will result from the length of the cannon and the amount of powder used. This amount will be limited only by the strength of the cannon. We must now decide on the dimensions of the cannon. Practically speaking, we can make it as strong as we like, because it won’t have to be moved.”
    “That’s all obvious,” said General Morgan.
    “So far the longest cannons made, our enormousColumbiads, have had a length of only twenty-five feet, so we’re going to surprise many people by the size we’ll have to adopt.”
    “I’m sure we will!” said J. T. Maston. “I think we ought to make our cannon at least half a mile long!”
    “Half a mile!” exclaimed the major and the general.
    “Yes, half a mile, and it still won’t be half long enough.”
    “Come, come, Maston,” said Morgan, “you’re exaggerating.”
    “I am not!” retorted the fiery secretary. “I don’t know how you can say a thing like that!”
    “I said it because you’re going too far.”
    “Sir,” J. T. Maston said loftily, “you’d do well to remember that an artilleryman is like a cannon ball: he can never go too far!”
    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