by Jules Verne
CHAPTER VII.
THE HYMN OF THE CANNON-BALL.
The Observatory of Cambridge in its memorable letter had treated thequestion from a purely astronomical point of view. The mechanical partstill remained.
President Barbicane had, without loss of time, nominated a WorkingCommittee of the Gun Club. The duty of this Committee was to resolve thethree grand questions of the cannon, the projectile, and the powder. Itwas composed of four members of great technical knowledge, Barbicane (witha casting vote in case of equality), General Morgan, Major Elphinstone,and J. T. Maston, to whom were confided the functions of secretary. Onthe 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 importantproblems in the whole of the noble science of gunnery. It might appear,perhaps, the most logical course to devote our first meeting to thediscussion of the engine to be employed. Nevertheless, after matureconsideration, it has appeared to me that the question of the projectilemust take precedence of that of the cannon, and that the dimensions ofthe latter must necessarily depend upon those of the former."
"Suffer me to say a word," here broke in J. T. Maston. Permissionhaving been granted, "Gentlemen," said he, with an inspired accent, "ourpresident is right in placing the question of the projectile above allothers. The ball we are about to discharge at the moon is our ambassadorto her, and I wish to consider it from a moral point of view. Thecannon-ball, gentlemen, to my mind, is the most magnificent manifestationof human power. If Providence has created the stars and the planets,man has called the cannon-ball into existence. Let Providence claimthe swiftness of electricity and of light, of the stars, the comets,and the planets, of wind and sound--we claim to have invented theswiftness of the cannon-ball, a hundred times superior to that of theswiftest horses or railway train. How glorious will be the moment when,infinitely exceeding all hitherto attained velocities, we shall launchour new projectile with the rapidity of seven miles a second! Shall itnot, gentlemen--shall it not be received up there with the honours dueto a terrestrial ambassador?"
Overcome with emotion the orator sat down and applied himself to a hugeplate of sandwiches before him.
"And now," said Barbicane, "let us quit the domain of poetry and comedirect 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 communicateto a projectile a velocity of 12,000 yards per second. Let us at presentexamine the velocities hitherto attained. General Morgan will be able toenlighten us on this point."
"And the more easily," replied the general, "that during the war I wasa member of the Committee of experiments. I may say, then, that the100-pounder Dahlgrens, which carried a distance of 5000 yards, impressedupon their projectile an initial velocity of 500 yards a second. TheRodman Columbiad threw a shot weighing half a ton a distance of sixmiles, with a velocity of 800 yards per second--a result which Armstrongand Palisser have never obtained in England."
"This," replied Barbicane, "is, I believe, the maximum velocity everattained?"
"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 ittwenty-fold. Now, reserving for another discussion the means of producingthis velocity, I will call your attention to the dimensions which it willbe proper to assign to the shot. You understand that we have nothing todo 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 toattract 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 takeno further notice of it; we must follow it throughout its course, up tothe moment when it shall reach its goal."
"What?" shouted the general and the major in great surprise.
"Undoubtedly," replied Barbicane composedly, "or our experiment wouldproduce no result."
"But then," replied the major, "you will have to give this projectileenormous dimensions."
"No! Be so good as to listen. You know that optical instruments haveacquired great perfection; with certain telescopes we have succeeded inobtaining enlargements of 6000 times and reducing the moon to within fortymiles' distance. Now, at this distance, any objects sixty feet squarewould be perfectly visible. If, then, the penetrative power of telescopeshas not been further increased, it is because that power detracts fromtheir light; and the moon, which is but a reflecting mirror, does notgive back sufficient light to enable us to perceive objects of lessermagnitude."
"Well, then, what do you propose to do?" asked the general. "Would yougive 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 atmospherethrough which the moon's light has to travel I shall have rendered herlight more intense. To effect that object it will be enough to establisha telescope on some elevated mountain. That is what we will do."
"I give it up," answered the major. "You have such a way of simplifyingthings. And what enlargement do you expect to obtain in this way?"
"One of 48,000 times, which should bring the moon within an apparentdistance of five miles; and, in order to be visible, objects need nothave a diameter of more than nine feet."
"So, then," cried J. T. Maston, "our projectile need not be more thannine feet in diameter."
"Let me observe, however," interrupted Major Elphinstone, "this willinvolve a weight such as--"
"My dear major," replied Barbicane, "before discussing its weight, permitme to enumerate some of the marvels which our ancestors have achieved inthis respect. I don't mean to pretend that the science of gunnery hasnot advanced, but it is as well to bear in mind that during the middleages they obtained results more surprising, I will venture to say, thanours. For instance, during the siege of Constantinople by Mahomet II.,in 1453, stone shot of 1900 lbs. weight were employed. At Malta, in thetime of the knights, there was a gun of the fortress of St. Elmo whichthrew a projectile weighing 2500 lbs. And, now, what is the extent ofwhat we have seen ourselves? Armstrong guns discharging shot of 500 lbs.,and the Rodman guns projectiles of half a ton! It seems, then, that ifprojectiles 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 theprogress 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 uponemploying?"
"Simply cast iron," said General Morgan.
"But," interrupted the major, "since the weight of a shot is proportionateto its volume, an iron ball of nine feet in diameter would be oftremendous 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 of108 inches would weigh more than 200,000 lbs., a weight evidently far toogreat. 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 108inches would require sides of two feet thickness, or less."
"That would be too much," replied Barbicane; "for you will observe thatthe question
is not that of a shot intended to pierce an iron plate: itwill suffice, therefore, to give it sides strong enough to resist thepressure of the gas. The problem, therefore, is this--What thicknessought a cast-iron shell to have in order not to weigh more than 20,000lbs.? 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.
"Aluminium!" replied Barbicane.
"Aluminium?" cried his three colleagues in chorus.
"Unquestionably, my friends. This valuable metal possesses the whitenessof silver, the indestructibility of gold, the tenacity of iron, thefusibility of copper, the lightness of glass. It is easily wrought, isvery widely distributed, forming the base of most of the rocks, is threetimes lighter than iron, and seems to have been created for the expresspurpose of furnishing us with the material for our projectile."
"But, my dear president," said the major, "is not the cost price ofaluminium extremely high?"
"It was so at its first discovery, but it has fallen now to nine dollarsthe pound."
"But still, nine dollars the pound!" replied the major, who was notwilling 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 of108 inches in diameter, and 12 inches in thickness, would weigh, incast-iron, 67,440 lbs.; cast in aluminium, its weight will be reduced to19,250 lbs."
"Capital!" cried the major; "but do you know that, at nine dollars thepound, 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 bewanting for our enterprise, I will answer for it. Now what say you toaluminium, gentlemen?"
"Adopted!" replied the three members of the Committee. So ended the firstmeeting. The question of the projectile was definitively settled.