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 1,900 pounds 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 2,500 pounds. And, now,
what is the extent of what we have seen ourselves? Armstrong guns
discharging shot of 500 pounds, 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
on science, at ten times the weight of the shot of Mahomet II.
and the Knights of Malta.”
“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; “decidely it must be. A solid
shot of 108 inches would weigh more than 200,000 pounds, 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 pounds.”
“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 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 weight more than 20,000 pounds? 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 formulae 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.
“Aluminum!” replied Barbicane.
“Aluminum?” 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 aluminum extremely high?”
“It was so at its first discovery, but it has fallen now to nine
dollars a pound.”
“But still, nine dollars a 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 twelve inches in
thickness, would weigh, in cast-iron, 67,440 pounds; cast in
aluminum, its weight will be reduced to 19,250 pounds.”