them to make us sink when we want to, and, what's more
important, to rise to the surface in a hurry. I've got time
enough to look them over before dad and Mr. Sharp get back."

Tom entered the starboard tank by means of an emergency
sliding door between the big compartments and the main part
of the ship. This was closed by a worm and screw gear, and
once the ship was in the water would seldom be used.

The young inventor proceeded with his task, carefully
inspecting the valves by the light of a lantern he carried.
The apparatus seemed to be all right, and Tom was about to
leave when a peculiar noise attracted his attention. It was
the sound of metal scraping on metal, and the lad's quick
and well-trained ear told him it was somewhere about the
ship.

He turned to leave the tank, but as he wheeled around his
light flashed on a solid wall of steel back of him. The
emergency outlet had been closed! He was a prisoner in the
water compartment, and he knew, from past experience, that
shout as he would, his voice could not be heard ten feet
away. His father and Mr. Sharp, as he was aware, had gone to
a nearby city for some tools, and Mr. Jackson, the engineer,
was temporarily away. Mrs. Baggert, in the house, could not
hear his cries.

"I'm locked in!" cried Tom aloud. "The worm gear must have
shut of itself. But I don't see how that could be. I've got
to get out mighty soon, though, or I'll smother. This tank