ny square inches are
there in a square foot?"

"One hundred and forty-four," replied Alfred.

"Then, eighty-five times one hundred and forty-four makes quite a sum,"
continued the captain.

"Whew,----" said Ralph with a half whistle in his tone, "why, if I have
made it out right, it's over 12,000 pounds. No wonder it isn't safe to
stay down very long, if at all, at that depth."

"I have often wondered how it is that the submarine could rest on the
bottom or come up at will," said Alfred.

"All submarines are lighter than the water in which they float,"
answered the captain. "They are provided with tanks holding compressed
air. Now, in order to submerge, the only thing necessary is to permit
enough water to flow into special tanks within the submarine, until the
combined weight of the water, hull and mechanism, is the same as the
amount of water that the ship displaces. If an added quantity of water
is now added, it will go down, and remain under water until the air in
the compressed tanks is used to force out a quantity of water from the
special tanks."

"But is that the only way they can go down?" asked Ralph.

"Oh, no; a submarine can submerge without doing that, but in such a case
power must be used," answered the captain.

"What! push it down by power?" asked Alfred.

"Exactly; these vessels have fins, the same as fish, so arranged that if
they are properly turned and the ship moves forward, it will dive, and
continue to go down at an angle as long as the fins are properly set. If
the vessel should stop moving the submarine would come to the top,
because it is lighter than the water," responded the captain.

CHAPTER V

SOME OF THE MYSTERIES OF A SUBMARINE

With a click the door of their prison cabin opened and a seaman informed
them that their breakfast was ready. They passed through the narrow
door, and edged their way along a tortuous path that led to the rear,
where they entered what might be called a miniature galley, on one side
of which was a narrow shelf containing food of various descriptions.

There was room only for the attendant to pass while they were seated. An
abundance of the best food was served, cereals, and even fruit, forming
part of the menu. Each of these vessels carry from twenty-two to thirty
men, but there were in sight in the dining room only ten, besides the
cook and waiter.

After the meal, the captain inquired of the officer at the main hatch
whether they would b