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,