From the Earth to the Moon; and, Round the Moon Read online

  CHAPTER VII

  HISTORY OF THE CANNON

  The resolutions passed at the last meeting produced a greateffect out of doors. Timid people took fright at the idea ofa shot weighing 20,000 pounds being launched into space; theyasked what cannon could ever transmit a sufficient velocity tosuch a mighty mass. The minutes of the second meeting weredestined triumphantly to answer such questions. The followingevening 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 probablethat we shall end by giving it gigantic dimensions; but howevergreat may be the difficulties in the way, our mechanical geniuswill readily surmount them. Be good enough, then, to give meyour attention, and do not hesitate to make objections at the close.I have no fear of them. The problem before us is how to communicatean initial force of 12,000 yards per second to a shell of 108inches in diameter, weighing 20,000 pounds. Now when a projectileis launched into space, what happens to it? It is acted upon bythree independent forces: the resistance of the air, the attractionof the earth, and the force of impulsion with which it is endowed.Let us examine these three forces. The resistance of the air is oflittle importance. The atmosphere of the earth does not exceedforty miles. Now, with the given rapidity, the projectile willhave traversed this in five seconds, and the period is too brieffor the resistance of the medium to be regarded otherwise thanas insignificant. Proceding, then, to the attraction of the earth,that is, the weight of the shell, we know that this weight willdiminish in the inverse ratio of the square of the distance.When a body left to itself falls to the surface of the earth, itfalls five feet in the first second; and if the same body wereremoved 257,542 miles further off, in other words, to the distanceof the moon, its fall would be reduced to about half a line in thefirst second. That is almost equivalent to a state of perfect rest.Our business, then, is to overcome progressively this actionof gravitation. The mode of accomplishing that is by the forceof impulsion."

  "There's the difficulty," broke in the major.

  "True," replied the president; "but we will overcome that, forthe force of impulsion will depend on the length of the engineand the powder employed, the latter being limited only by theresisting power of the former. Our business, then, to-day iswith the dimensions of the cannon."

  "Now, up to the present time," said Barbicane, "our longest gunshave not exceeded twenty-five feet in length. We shalltherefore astonish the world by the dimensions we shall beobliged to adopt. It must evidently be, then, a gun of greatrange, since the length of the piece will increase the detentionof the gas accumulated behind the projectile; but there is noadvantage in passing certain limits."

  "Quite so," said the major. "What is the rule in such a case?"

  "Ordinarily the length of a gun is twenty to twenty-five timesthe diameter of the shot, and its weight two hundred andthirty-five to two hundred and forty 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 thisproportion for a projectile nine feet in diameter, weighing 30,000pounds, the gun would only have a length of two hundred and twenty-five feet, and a weight of 7,200,000 pounds."

  "Ridiculous!" rejoined Maston. "As well take a pistol."

  "I think so too," replied Barbicane; "that is why I propose toquadruple that length, and to construct a gun of nine hundred feet."

  The general and the major offered some objections; nevertheless,the proposition, actively supported by the secretary, wasdefinitely 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 acarriage?" asked the major.

  "It would be a superb idea, though," said Maston.

  "But impracticable," replied Barbicane. "No, I think of sinkingthis engine in the earth alone, binding it with hoops of wroughtiron, and finally surrounding it with a thick mass of masonry ofstone and cement. The piece once cast, it must be bored withgreat precision, so as to preclude any possible windage. So therewill be no loss whatever of gas, and all the expansive force ofthe 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 enormousinitial velocity; and you are well aware that a shot quits arifled 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 inoxidable by thecorrosive action of acids."

  "There is no doubt about that," replied the major; "and as weshall have to employ an immense quantity of metal, we shall notbe at a loss for choice."

  "Well, then," said Morgan, "I propose the best alloy hithertoknown, which consists of one hundred parts of copper, twelve oftin, and six of brass."

  "I admit," replied the president, "that this composition hasyielded excellent results, but in the present case it would betoo expensive, and very difficult to work. I think, then, thatwe ought to adopt a material excellent in its way and of lowprice, such as cast iron. What is your advice, major?"

  "I quite agree with you," replied Elphinstone.

  "In fact," continued Barbicane, "cast iron costs ten times lessthan bronze; it is easy to cast, it runs readily from the mouldsof sand, it is easy of manipulation, it is at once economical ofmoney and of time. In addition, it is excellent as a material,and I well remember that during the war, at the siege ofAtlanta, some iron guns fired one thousand rounds at intervalsof twenty minutes without injury."

  "Cast iron is very brittle, though," replied Morgan.

  "Yes, but it possesses great resistance. I will now ask ourworthy secretary to calculate the weight of a cast-iron gun witha bore of nine feet and a thickness of six feet of metal."

  "In a moment," replied Maston. Then, dashing off somealgebraical formulae with marvelous facility, in a minute or twohe declared the following result:

  "The cannon will weigh 68,040 tons. And, at two cents a pound,it will cost----"

  "Two million five hundred and ten thousand seven hundred andone dollars."

  Maston, the major, and the general regarded Barbicane withuneasy looks.

  "Well, gentlemen," replied the president, "I repeat what Isaid yesterday. Make yourselves easy; the millions will notbe wanting."

  With this assurance of their president the committee separated,after having fixed their third meeting for the following evening.