keel."

"Gracious! You meant those eighteen feet, didn't you? It wasn't
accident?" gasped Eph.

"We meant it," smiled the builder. "But say, the air is getting a bit
foul here, isn't it? We'll have to try the compressed air equipment,
now."

By an ingenious mechanical contrivance the present air was forced, by
compressed air draught, into compartments from which the bad air was
expelled through sea-valves. An instant change for the better in the
atmosphere was noted.

"That's another thing about this good old new craft of ours that works
all right, so far," remarked the builder. "Boys, I'm beginning to have
confidence that we're going to see the surface again all right. Hullo,
there's Pollard hailing us."

"The air purified all right, didn't it?" called down the inventor.

"Yes; couldn't have been better," declared the builder heartily.

"Then I'm going to make the supreme test," came down from the man at
the wheel. "We'll proceed to find out whether we can rise to the
surface and stay there."

CHAPTER XII

THE DISCOVERY FROM THE CONNING TOWER

"Go up slanting, or on an even keel?" called up Mr. Farnum.

"On the even keel," came the answer.

"All right, then; we'll know soon."

For this purpose the largest compressed air container of all was to be
employed. It distributed great volumes of compressed air to all the
water tanks, forcing open the valves and driving out the water.

"Any of you youngsters know where the proper wrench is?" inquired the
builder, looking keenly at the boys.

There was an instant start, followed by widespread pallor.

"Oh, it's not right to keep you in torment," laughed the builder. "I
have kept the wrench in my pocket, all along."

He drew it out, holding it up before their gaze. Though technically
a wrench, it looked more like a very large key. It was of curious
construction, intended to supply the greatest amount of force with the
least amount of exertion.

"Watch me," commanded Jacob Farnum. "Any one of you may have to use
this wrench at any time."

Little did any of them guess the tragedy that was destined to center
around that life-saving wrench later on. Now, with the boys gathered
about him, Mr. Farnum fitted the wrench with great care and deliberation.

"See how easily it's intended to turn?" asked the builder, giving it a
slight turn.

All three of the boys nodded.

"Now, we'll give it more," continued Mr. Farnum. He swung the wrench