"Then we shall have to come back to my cannon half a mile long."

"It is evident," said the major.

"Sixteen hundred thousand pounds of powder," resumed the Secretary of
Committee, "will occupy about a space of 22,000 cubic feet; now, as your
cannon will only hold about 54,000 cubic feet, it will be half full, and
the chamber will not be long enough to allow the explosion of the gas to
give sufficient impulsion to your projectile."

There was nothing to answer. J.T. Maston spoke the truth. They all
looked at Barbicane.

"However," resumed the president, "I hold to that quantity of powder.
Think! 1,600,000 pounds of powder will give 6,000,000,000 litres of
gas."

"Then how is it to be done?" asked the general.

"It is very simple. We must reduce this enormous quantity of powder,
keeping at the same time its mechanical power."

"Good! By what means?"

"I will tell you," answered Barbicane simply.

His interlocutors all looked at him.

"Nothing is easier, in fact," he resumed, "than to bring that mass of
powder to a volume four times less. You all know that curious cellular