ch interested in the simple recital.

"The result of the introduction of the spark is the explosion of the
compressed vapor, which sends the piston downward. The motion turns the
shaft, and that turns the boat's propeller."

"Easy as pie."

"This operation is repeated from two to six hundred times a minute,"
Jack went on, "and that causes the continuous action of the machinery
which sends the boat along."

"What is there about that so complicated?" demanded Frank. "Everybody
you hear talking of an engine seems to speak as if it were one of the
mysteries of the universe."

"It is usually the electric system which gets out of order," was the
reply, "but sometimes the gasoline section balks. A man often has to try
so many different things when his engine stops that he actually does not
know which one remedies the evil and sets the thing in motion."

"All right!" Frank said. "Now show me how to start the thing."

"That's easy. First turn on your gasoline, as you would turn water from
a faucet into a kitchen sink. The gasoline fills the carbureter, which
is the thing which feeds the engine automatically. Then you turn on your
electricity by shifting a switch. That is to supply the spark. Then turn
the fly-wheel two or three times so as to get the vapor into the
cylinder and secure the first explosion. That is all there is to it. I
hope you do learn to run this boat, so I can get away now and then!"

"You may get away farther than you want to!" cautioned Frank.

The _Manhattan_ was a plain, usable boat, twenty-five feet long and ten
feet wide, with bow and stern rather square in order to make more room
inside. The cabin was ten feet long, with strong oak sides and
brass-rimmed ports for light and ventilation. The cockpit, or outdoor
sitting room, was of the same length as the cabin.

The engine was a plain, solidly built machine, with two cylinders, and
rated at ten horsepower, with a speed of fifteen miles an hour. It was
installed under a short bridge-deck in front of the cabin, while the
gasoline tanks, holding fifty gallons, were hidden under the cockpit
seats.

The cabin had two wide slatted berths, supplied with hair mattresses, a
movable table, an ice chest, a small coal range--the boat was not
designed especially for tropical use--an ice-chest and an alcohol stove
for cooking. The storage lockers and water tanks had a capacity of a
week's supply of stores for four persons. It was a government boat, and
wa