the cover back on.

How they inserted the bolts and screwed the nuts in place they never
could remember clearly afterward, but they managed it somehow, with
shaking, trembling hands and eyes that grew more and more dim.

"Now start the pumps!" cried Tom faintly. "The tanks will be emptied,
and we can get to the surface."

Mr. Sharp was still unconscious, nor was Mr. Swift able to help. He lay
with his eyes closed. Garret Jackson, however, managed to crawl to the
engine-room, and soon the clank of machinery told Tom that the pumps
were in motion. The lad staggered to the pilot house and threw the
levers over. An instant later there was the hissing of water as it
rushed from the ballast tanks. The submarine shivered, as though
disliking to leave the bottom of the sea, and then slowly rose. As the
pumps worked more rapidly, and the sea was sent from the tank in great
volumes, the boat fairly shot to the surface. Tom was ready to open the
conning tower and let in fresh air as soon as the top was above the
surface.

With a bound the Advance reached the top. Tom frantically worked the
worm gear that opened the tower. In rushed the fresh, life-giving air,
and the treasure-hunters filled their lungs with it.

And it was only just in time, for Mr. Sharp was almost gone. He quickly
revived, as did the others, when they could breathe as much as they
wished of the glorious oxygen.

"That was a close call," commented Mr. Swift. "We'll not go below again
until I have provided for all emergencies. I should have seen to the
air tanks and the expanding one before going below. We'll sail home on
the surface now."

The submarine was put about and headed for her dock. On the way she
passed a small steamer, and the passengers looked down in wonder at the
strange craft.

When the Advance reached the secluded creek where she had been
launched, her passengers had fully recovered from their terrible
experience, though the nerves of Mr. Swift and Mr. Damon were not at
ease for some days thereafter.

"I should never have made a submerged test without making sure that we
had a reserve supply of air," remarked the aged inventor. "I will not
be caught that way again. But I can't understand how the pump valve got
out of order."

"Maybe some one tampered with it," suggested Mr. Damon. "Could Andy
Foger, any of the Happy Harry gang, or the rival gold-seekers have done
it?"

"I hardly think so," answered Tom. "The place has been too care