“If we go much deeper, I’ll sure let out a yell,” Eph gritted, between his teeth.

At last Jack’s voice broke in, coolly: 

“You see, gentlemen, the gauge now gives a constant reading.  We can’t go any lower, for the water tanks are as full as they’ll hold, and there’s still the buoyancy caused by all the air the interior of the boat.  So we’re as far below the surface as we can go.”

“Bully for you, Benson!” cried Lieutenant McCrea, slapping the young skipper on the back.  “You understand what you’re doing, and no one could do it with more coolness.  You must have been born aboard a submarine.”

“He never saw a craft of this kind, until a few weeks ago,” retorted Jacob Farnum admiringly.

Taking out a notebook and pencil, Commander Ennerling recorded the reading of the submergence gauge, which showed how many feet the craft was below the surface of the water.

“Of course,” hinted Mr. Farnum, smilingly, “don’t know the gauge to be correct.”

“We’ve the means with us of testing and standardizing the gauge in the harbor,” replied the president of the board.

“If we ever see the harbor again,” muttered Eph Somers, overhead in the conning tower.

“How does this compare with the depths touched by submarine boats now owned by the Navy?” asked David Pollard, a bit feverishly.  He was not afraid of their present rather dangerous position, but was frightfully nervous over the thought of any good showing this craft born in his brain might fail to make.  “This is thirty feet lower than any submarine record I’ve ever heard of.”

“I—­perhaps it would be wiser for me not to say,” replied Commander Ennerling.  “It may be as well for me to wait and compare this record with those on file at the Navy Department.”

“Have you had all you want of this, gentlemen?” inquired the boatbuilder.  “Shall we show you anything else?”

“Yes; you might give us a run at full speed under water, at the lowest depth that you deem it wise to try to run the craft,” answered the president of the board.

“Very good,” nodded the builder.  Hal took this as the signal to leap back into the motor room.

“How far below the surface would you dare run the ‘Pollard,’ Captain Benson?” inquired Commander Ennerling.

“At the greatest depth we can go, the present depth,” quietly answered Jack, without bravado.

The president of the board glanced at the builder of the submarine.

“Does that appeal to you, Mr. Farnum?”

“I’ll let Captain Benson have his own way, unless the members of the board have other instructions,” replied Jacob Farnum, promptly.

“Well, Captain Benson, if you deem it wise to work your propellers at their best at the present level, go ahead and try it,” laughed the president of the board.

“Half speed ahead, Hal,” called the young submarine captain.  “Full speed as soon as you get well started.  Eph, swing around and go due west.”