HISTORY OF THE CANNON.
The resolutions passed at the last meeting produced a great effect
out of doors. Timid people took fright at the idea of a shot weighing
20,000 lbs. being launched into space; they asked what cannon could ever
transmit a sufficient velocity to such a mighty mass. The minutes of the
second meeting were destined triumphantly to answer such questions. The
following evening the discussion was renewed.
"My dear colleagues," said Barbicane, without further preamble, "the
subject now before us is the construction of the engine, its length, its
composition, and its weight. It is probable that we shall end by giving
it gigantic dimensions; but however great may be the difficulties in the
way, our mechanical genius will readily surmount them. Be good enough,
then, to give me your attention, and do not hesitate to make objections
at the close. I have no fear of them. The problem before us is how to
communicate an initial force of 12,000 yards per second to a shell of 108
inches in diameter, weighing 20,000 lbs. Now when a projectile is launched
into space, what happens to it? It is acted upon by three independent
forces, the resistance of the air, the attraction of the earth, and the
force of impulsion with which it is endowed. Let us examine these three
forces. The resistance of the air is of little importance. The atmosphere
of the earth does not exceed forty miles. Now, with the given rapidity,
the projectile will have traversed this in five seconds, and the period
is too brief for the resistance of the medium to be regarded otherwise
than as insignificant. Proceeding, then, to the attraction of the earth,
that is, the weight of the shell, we know that this weight will diminish
in the inverse ratio of the square of the distance. When a body left to
itself falls to the surface of the earth, it falls five feet in the first
second; and if the same body were removed 257,542 miles farther off, in
other words, to the distance of the moon, its fall would be reduced to
about half a line in the first second. That is almost equivalent to a
state of perfect rest. Our business, then, is to overcome progressively
this action of gravitation. The mode of accomplishing that is by the
force of impulsion."
"There's the difficulty," broke in the major.
"True," replied the president; "but we will overcome that, for this force
of impulsion will depend upon the length of the engine and the powder
employed, the latter being limited only by the resisting power of the
former. Our business, then, to-day is with the dimensions of the cannon."
"Now, up to the present time," said Barbicane, "our longest guns have
not exceeded twenty-five feet in length. We shall therefore astonish the
world by the dimensions we shall be obliged to adopt. It must evidently
be, then, a gun of great range, since the length of the piece will
increase the detention of the gas accumulated behind the projectile; but
there is no advantage in passing certain limits."
"Quite so," said the major. "What is the rule in such a case?"
"Ordinarily the length of a gun is 20 to 25 times the diameter of the
shot, and its weight 235 to 240 times that of the shot."
"That is not enough," cried J. T. Maston impetuously.
"I agree with you, my good friend; and, in fact, following this proportion
for a projectile nine feet in diameter, weighing 30,000 lbs., the gun
would only have a length of 225 feet, and a weight of 7,200,000 lbs."
"Ridiculous!" rejoined Maston. "As well take a pistol."
"I think so too," replied Barbicane; "that is why I propose to quadruple
that length, and to construct a gun of 900 feet."
The general and the major offered some objections; nevertheless, the
proposition, actively supported by the secretary, was definitively
adopted.
"But," said Elphinstone, "what thickness must we give it?"
"A thickness of six feet," replied Barbicane.
"You surely don't think of mounting a mass like that upon a carriage?"
asked the major.
"It would be a superb idea, though," said Maston.
"But impracticable," replied Barbicane. "No; I think of sinking this
engine in the earth alone, binding it with hoops of wrought iron, and
finally surrounding it with a thick mass of masonry of stone and cement.
The piece once cast, it must be bored with great precision, so as to
preclude any possible windage. So there will be no loss whatever of
gas, and all the expansive force of the powder will be employed in the
propulsion."
"One simple question," said Elphinstone: "is our gun to be rifled?"
"No, certainly not," replied Barbicane; "we require an enormous initial
velocity; and you are well aware that a shot quits a rifled gun less
rapidly than it does a smooth-bore."
"True," rejoined the major.
The Committee here adjourned for a few minutes to tea and sandwiches.
On the discussion being renewed, "Gentlemen," said Barbicane, "we must
now take into consideration the metal to be employed. Our cannon must
be possessed of great tenacity, great hardness, be infusible by heat,
indissoluble, and inoxydable by the corrosive action of acids."
"There is no doubt about that," replied the major; "and as we shall have
to employ an immense quantity of metal, we shall not be at a loss for
choice."
Illustration: IDEAL SKETCH OF J. T. MASTON'S GUN.
"Well, then," said Morgan, "I propose the best alloy hitherto known,
which consists of 100 parts of copper, 12 of tin, and 6 of brass."
"I admit," replied the president, "that this composition has yielded
excellent results, but in the present case it would be too expensive, and
very difficult to work. I think, then, that we ought to adopt a material
excellent in its way and of low price, such as cast iron. What is your
advice, major?"
"I quite agree with you," replied Elphinstone.
"In fact," continued Barbicane, "cast iron cost ten times less than
bronze; it is easy to cast, it runs readily from the moulds of sand,
it is easy of manipulation, it is at once economical of money and of
time. In addition, it is excellent as a material, and I well remember
that during the war, at the siege of Atlanta, some iron guns fired one
thousand rounds at intervals of twenty minutes without injury."
"Cast iron is very brittle, though," replied Morgan.
"Yes, but it possesses great resistance. I will now ask our worthy
secretary to calculate the weight of a cast-iron gun with a bore of nine
feet and a thickness of six feet of metal."
"In a moment," replied Maston. Then, dashing off some algebraical formulæ
with marvellous facility, in a minute or two he declared the following
result:—
"The cannon will weigh 68,040 tons. And, at two cents a pound, it will
cost—?"
"2,510,701 dollars."
Maston, the major, and the general regarded Barbicane with uneasy looks.
"Well, gentlemen," replied the president, "I repeat what I said yesterday.
Make yourselves easy; the millions will not be wanting."
With this assurance of their president the Committee separated, after
having fixed their third meeting for the following evening.