We evidently want a gun of great range, as the length of the engine will increase the detention of gas accumulated behind the projectile, but it is useless to overstep certain limits." "Perfectly," said the major.
"What are the usual rules in such a case?
Ordinarily the length of a cannon is twenty or twenty-five times the diameter of the projectile, and it weighs 235 to 240 times its weight." "It is not enough," cried J.T.Maston with impetuosity.
"I agree to that, my worthy friend, and in fact by keeping that proportion for a projectile nine feet wide, weighing 30,000 lbs., the engine would only have a length of 225 feet and a weight of 7,200,000 lbs." "That is ridiculous," resumed J.T.Maston.

"You might as well take a pistol." "I think so too," answered Barbicane; "that is why I propose to quadruple that length, and to construct a cannon 900 feet long." The general and the major made some objections, but, nevertheless, this proposition, strongly supported by the secretary, was definitely adopted.
"Now," said Elphinstone, "what thickness must we give its sides ?" "A thickness of six feet," answered Barbicane.
"You do not think of raising such a mass upon a gun-carriage ?" asked the major.
"That would be superb, however! said J.T.

Maston.
"But impracticable," answered Barbicane.

"No, I think of casting this engine in the ground itself, binding it up with wrought-iron hoops, and then surrounding it with a thick mass of stone and cement masonry.

When it is cast it must be bored with great precision so as to prevent windage, so there will be no loss of gas, and all the expansive force of the powder will be employed in the propulsion." "Hurrah! hurrah!" said Maston, "we have our cannon." "Not yet," answered Barbicane, calming his impatient friend with his hand.
"Why not ?" "Because we have not discussed its form.