on his mind
that we were all great sinners, and that he'd save the whole lot of us
by killing us under water."

"It seems strange," muttered Hal, "for even a crazy man to have the
nerve to destroy himself slowly in such a way."

"Humph, no; nothing new in that line," returned Mr. Farnum.

"What are we going to do with him, sir?" inquired Captain Jack.

"Well, we're not going to turn in at any of the coast towns to give
him up," replied the builder. "We'll keep right along until we join
the fleet, and then we'll ask the advice of some naval officer."

When, at last, all had become accustomed to the world to which they
had returned, Hal and Eph went below, to turn on the gasoline power a
short time the "Pollard" was kicking the water at the exhilarating gait
of eighteen miles an hour.

"How did it come, sir, that you made it eighteen miles, instead of
knots?" asked Captain Jack, after a while.

"Why, that's the basis on which gasoline engines are built," replied
Mr. Farnum. "For that matter, captain, when we've had more practice
with this boat we'll tune the engine up to eighteen full knots an hour.
In the second boat we are going to try for an assured speed of
twenty-two to twenty-four knots."

"It seems to me," said Jack, musingly, "that the ideal submarine torpedo
boat ought to have a speed of from twenty-eight, to thirty-five knots."

"Why?"

"So that the speed of the submarine boat shall always be ahead of the
speed of any battleship afloat."

"Again, why?"

"Why, so that the submarine can give effective chase to a battleship."

"But submarines are intended only to go with fleets of their own country,
or else to remain on station at or near the mouths of harbors to be
defended."

"All well and good," argued Captain Jack, nodding. "In future wars a
battleship fleet is likely to keep away from any harbor known to be
defended by the enemy's submarine boats. But, if a submarine torpedo
boat could have speed enough to give chase to a fleeing battleship, and
sink when within range of the battleship's guns, yet still be able to
pursue, under water, and destroy the battleship, that would mean the
day when battleships wouldn't be of any further use, wouldn't it?"

"Undoubtedly," admitted Mr. Farnum. "But you see, captain, so far
as present human ingenuity goes, a boat can't be built to sail as
fast under water as another can be made to go on the surface."

"But that's the problem I'm going to tackle,