prompted him to study the various subjects included in this science,
and as he stood by his companion, the pilot, he talked quite
learnedly about the specific gravity of wood and iron, about
displacement, buoyancy, and similar topics.

"The hull of the steamer--that is, the woodwork--will not float
itself, but it will sustain considerable additional weight," said he.

"Yes, I understand all that," replied Lawry. "If there had been no
iron in the _Woodville_ she would not have gone down."

"The iron in her engines is seven or eight times as heavy as the
same bulk of water. Its weight carried the hull down with it."

"Then we must put down empty casks enough to float the engine,"
added Lawry.

"No; the woodwork of the hull will hold up a portion of the weight
of the engine, and we must furnish buoyancy enough to sustain the
rest of it."

"It will not take a great many casks, then--will it?"

"Not a great many; but the difficulty is to get them down to the
bottom, and fasten them to the hull."

"I can do that," replied Lawry confidently.

Ethan approved the method, and promised to ascertain what weight
each of the casks would sustain in the water, when he had obtained