by Jules Verne
CHAPTER VIII.
HISTORY OF THE CANNON.
The resolutions passed at the last meeting produced a great effectout of doors. Timid people took fright at the idea of a shot weighing20,000 lbs. being launched into space; they asked what cannon could evertransmit a sufficient velocity to such a mighty mass. The minutes of thesecond meeting were destined triumphantly to answer such questions. Thefollowing evening the discussion was renewed.
"My dear colleagues," said Barbicane, without further preamble, "thesubject now before us is the construction of the engine, its length, itscomposition, and its weight. It is probable that we shall end by givingit gigantic dimensions; but however great may be the difficulties in theway, our mechanical genius will readily surmount them. Be good enough,then, to give me your attention, and do not hesitate to make objectionsat the close. I have no fear of them. The problem before us is how tocommunicate an initial force of 12,000 yards per second to a shell of 108inches in diameter, weighing 20,000 lbs. Now when a projectile is launchedinto space, what happens to it? It is acted upon by three independentforces, the resistance of the air, the attraction of the earth, and theforce of impulsion with which it is endowed. Let us examine these threeforces. The resistance of the air is of little importance. The atmosphereof the earth does not exceed forty miles. Now, with the given rapidity,the projectile will have traversed this in five seconds, and the periodis too brief for the resistance of the medium to be regarded otherwisethan as insignificant. Proceeding, then, to the attraction of the earth,that is, the weight of the shell, we know that this weight will diminishin the inverse ratio of the square of the distance. When a body left toitself falls to the surface of the earth, it falls five feet in the firstsecond; and if the same body were removed 257,542 miles farther off, inother words, to the distance of the moon, its fall would be reduced toabout half a line in the first second. That is almost equivalent to astate of perfect rest. Our business, then, is to overcome progressivelythis action of gravitation. The mode of accomplishing that is by theforce of impulsion."
"There's the difficulty," broke in the major.
"True," replied the president; "but we will overcome that, for this forceof impulsion will depend upon the length of the engine and the powderemployed, the latter being limited only by the resisting power of theformer. Our business, then, to-day is with the dimensions of the cannon."
"Now, up to the present time," said Barbicane, "our longest guns havenot exceeded twenty-five feet in length. We shall therefore astonish theworld by the dimensions we shall be obliged to adopt. It must evidentlybe, then, a gun of great range, since the length of the piece willincrease the detention of the gas accumulated behind the projectile; butthere 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 theshot, 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 proportionfor a projectile nine feet in diameter, weighing 30,000 lbs., the gunwould 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 quadruplethat length, and to construct a gun of 900 feet."
The general and the major offered some objections; nevertheless, theproposition, actively supported by the secretary, was definitivelyadopted.
"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 thisengine in the earth alone, binding it with hoops of wrought iron, andfinally 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 topreclude any possible windage. So there will be no loss whatever ofgas, and all the expansive force of the powder will be employed in thepropulsion."
"One simple question," said Elphinstone: "is our gun to be rifled?"
"No, certainly not," replied Barbicane; "we require an enormous initialvelocity; and you are well aware that a shot quits a rifled gun lessrapidly 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 mustnow take into consideration the metal to be employed. Our cannon mustbe 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 haveto employ an immense quantity of metal, we shall not be at a loss forchoice."
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 yieldedexcellent results, but in the present case it would be too expensive, andvery difficult to work. I think, then, that we ought to adopt a materialexcellent in its way and of low price, such as cast iron. What is youradvice, major?"
"I quite agree with you," replied Elphinstone.
"In fact," continued Barbicane, "cast iron cost ten times less thanbronze; 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 oftime. In addition, it is excellent as a material, and I well rememberthat during the war, at the siege of Atlanta, some iron guns fired onethousand 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 worthysecretary to calculate the weight of a cast-iron gun with a bore of ninefeet and a thickness of six feet of metal."
"In a moment," replied Maston. Then, dashing off some algebraical formulaewith marvellous facility, in a minute or two he declared the followingresult:--
"The cannon will weigh 68,040 tons. And, at two cents a pound, it willcost--?"
"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, afterhaving fixed their third meeting for the following evening.
