THE HYMN OF THE CANNON-BALL.
The Observatory of Cambridge in its memorable letter had treated the
question from a purely astronomical point of view. The mechanical part
still remained.
President Barbicane had, without loss of time, nominated a Working
Committee of the Gun Club. The duty of this Committee was to resolve the
three grand questions of the cannon, the projectile, and the powder. It
was composed of four members of great technical knowledge, Barbicane (with
a casting vote in case of equality), General Morgan, Major Elphinstone,
and J. T. Maston, to whom were confided the functions of secretary. On
the 8th of October the Committee met at the house of President Barbicane,
3, Republican Street. The meeting was opened by the president himself.
"Gentlemen," said he, "we have to resolve one of the most important
problems in the whole of the noble science of gunnery. It might appear,
perhaps, the most logical course to devote our first meeting to the
discussion of the engine to be employed. Nevertheless, after mature
consideration, it has appeared to me that the question of the projectile
must take precedence of that of the cannon, and that the dimensions of
the latter must necessarily depend upon those of the former."
"Suffer me to say a word," here broke in J. T. Maston. Permission
having been granted, "Gentlemen," said he, with an inspired accent, "our
president is right in placing the question of the projectile above all
others. The ball we are about to discharge at the moon is our ambassador
to her, and I wish to consider it from a moral point of view. The
cannon-ball, gentlemen, to my mind, is the most magnificent manifestation
of human power. If Providence has created the stars and the planets,
man has called the cannon-ball into existence. Let Providence claim
the swiftness of electricity and of light, of the stars, the comets,
and the planets, of wind and sound—we claim to have invented the
swiftness of the cannon-ball, a hundred times superior to that of the
swiftest horses or railway train. How glorious will be the moment when,
infinitely exceeding all hitherto attained velocities, we shall launch
our new projectile with the rapidity of seven miles a second! Shall it
not, gentlemen—shall it not be received up there with the honours due
to a terrestrial ambassador?"
Overcome with emotion the orator sat down and applied himself to a huge
plate of sandwiches before him.
"And now," said Barbicane, "let us quit the domain of poetry and come
direct to the question."
"By all means," replied the members, each with his mouth full of sandwich.
"The problem before us," continued the president, "is how to communicate
to a projectile a velocity of 12,000 yards per second. Let us at present
examine the velocities hitherto attained. General Morgan will be able to
enlighten us on this point."
"And the more easily," replied the general, "that during the war I was
a member of the Committee of experiments. I may say, then, that the
100-pounder Dahlgrens, which carried a distance of 5000 yards, impressed
upon their projectile an initial velocity of 500 yards a second. The
Rodman Columbiad threw a shot weighing half a ton a distance of six
miles, with a velocity of 800 yards per second—a result which Armstrong
and Palisser have never obtained in England."
"This," replied Barbicane, "is, I believe, the maximum velocity ever
attained?"
"It is so," replied the general.
Illustration: THE RODMAN COLUMBIAD.
"Ah!" groaned J. T. Maston, "if my mortar had not burst—"
"Yes," quietly replied Barbicane, "but it did burst. We must take, then,
for our starting-point this velocity of 800 yards. We must increase it
twenty-fold. Now, reserving for another discussion the means of producing
this velocity, I will call your attention to the dimensions which it will
be proper to assign to the shot. You understand that we have nothing to
do here with projectiles weighing at most but half a ton."
"Why not?" demanded the major.
"Because the shot," quickly replied J. T. Maston, "must be big enough to
attract the attention of the inhabitants of the moon, if there are any?"
"Yes," replied Barbicane, "and for another reason more important still."
"What mean you?" asked the major.
"I mean that it is not enough to discharge a projectile, and then take
no further notice of it; we must follow it throughout its course, up to
the moment when it shall reach its goal."
"What?" shouted the general and the major in great surprise.
"Undoubtedly," replied Barbicane composedly, "or our experiment would
produce no result."
"But then," replied the major, "you will have to give this projectile
enormous dimensions."
"No! Be so good as to listen. You know that optical instruments have
acquired great perfection; with certain telescopes we have succeeded in
obtaining enlargements of 6000 times and reducing the moon to within forty
miles' distance. Now, at this distance, any objects sixty feet square
would be perfectly visible. If, then, the penetrative power of telescopes
has not been further increased, it is because that power detracts from
their light; and the moon, which is but a reflecting mirror, does not
give back sufficient light to enable us to perceive objects of lesser
magnitude."
"Well, then, what do you propose to do?" asked the general. "Would you
give your projectile a diameter of sixty feet?"
"Not so."
"Do you intend, then, to increase the luminous power of the moon?"
"Exactly so. If I can succeed in diminishing the density of the atmosphere
through which the moon's light has to travel I shall have rendered her
light more intense. To effect that object it will be enough to establish
a telescope on some elevated mountain. That is what we will do."
"I give it up," answered the major. "You have such a way of simplifying
things. And what enlargement do you expect to obtain in this way?"
"One of 48,000 times, which should bring the moon within an apparent
distance of five miles; and, in order to be visible, objects need not
have a diameter of more than nine feet."
"So, then," cried J. T. Maston, "our projectile need not be more than
nine feet in diameter."
"Let me observe, however," interrupted Major Elphinstone, "this will
involve a weight such as—"
"My dear major," replied Barbicane, "before discussing its weight, permit
me to enumerate some of the marvels which our ancestors have achieved in
this respect. I don't mean to pretend that the science of gunnery has
not advanced, but it is as well to bear in mind that during the middle
ages they obtained results more surprising, I will venture to say, than
ours. For instance, during the siege of Constantinople by Mahomet II.,
in 1453, stone shot of 1900 lbs. weight were employed. At Malta, in the
time of the knights, there was a gun of the fortress of St. Elmo which
threw a projectile weighing 2500 lbs. And, now, what is the extent of
what we have seen ourselves? Armstrong guns discharging shot of 500 lbs.,
and the Rodman guns projectiles of half a ton! It seems, then, that if
projectiles have gained in range, they have lost far more in weight. Now,
if we turn our efforts in that direction, we ought to arrive, with the
progress of science, at ten times the weight of the shot of Mahomet II.
and the Knights of Malta."
Illustration: CANNON AT MALTA IN THE TIME OF THE KNIGHTS.
"Clearly," replied the major; "but what metal do you calculate upon
employing?"
"Simply cast iron," said General Morgan.
"But," interrupted the major, "since the weight of a shot is proportionate
to its volume, an iron ball of nine feet in diameter would be of
tremendous weight."
"Yes, if it were solid, not if it were hollow."
"Hollow? then it would be a shell?"
"Yes, a shell," replied Barbicane; "decidedly it must be. A solid shot of
108 inches would weigh more than 200,000 lbs., a weight evidently far too
great. Still, as we must reserve a certain stability for our projectile,
I propose to give it a weight of 20,000 lbs."
"What, then, will be the thickness of the sides?" asked the major.
"If we follow the usual proportion," replied Morgan, "a diameter of 108
inches would require sides of two feet thickness, or less."
"That would be too much," replied Barbicane; "for you will observe that
the question is not that of a shot intended to pierce an iron plate: it
will suffice, therefore, to give it sides strong enough to resist the
pressure of the gas. The problem, therefore, is this—What thickness
ought a cast-iron shell to have in order not to weigh more than 20,000
lbs.? Our clever secretary will soon enlighten us upon this point."
"Nothing easier," replied the worthy secretary of the Committee; and,
rapidly tracing a few algebraical formulæ upon paper, among which _n_²
and _x_² frequently appeared, he presently said,—
"The sides will require a thickness of less than two inches."
"Will that be enough?" asked the major doubtfully.
"Clearly not!" replied the president.
"What is to be done, then?" said Elphinstone, with a puzzled air.
"Employ another metal instead of iron."
"Copper?" said Morgan.
"No; that would be too heavy. I have better than that to offer."
"What then?" asked the major.
"Aluminium!" replied Barbicane.
"Aluminium?" cried his three colleagues in chorus.
"Unquestionably, my friends. This valuable 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, is
very widely distributed, forming the base of most of the rocks, is three
times lighter than iron, and seems to have been created for the express
purpose of furnishing us with the material for our projectile."
"But, my dear president," said the major, "is not the cost price of
aluminium extremely high?"
"It was so at its first discovery, but it has fallen now to nine dollars
the pound."
"But still, nine dollars the pound!" replied the major, who was not
willing readily to give in; "even that is an enormous price."
"Undoubtedly, my dear major; but not beyond our reach."
"What will the projectile weigh then?" asked Morgan.
"Here is the result of my calculations," replied Barbicane. "A shot of
108 inches in diameter, and 12 inches in thickness, would weigh, in
cast-iron, 67,440 lbs.; cast in aluminium, its weight will be reduced to
19,250 lbs."
"Capital!" cried the major; "but do you know that, at nine dollars the
pound, this projectile will cost—"
"One hundred and seventy-three thousand and fifty dollars ($173,050).
I know it quite well. But fear not, my friends; the money will not be
wanting for our enterprise, I will answer for it. Now what say you to
aluminium, gentlemen?"
"Adopted!" replied the three members of the Committee. So ended the first
meeting. The question of the projectile was definitively settled.