“We’re doing well enough on top of the water,” he muttered, hoarsely, at last, to the builder.  “But will the boat dive?  How will she run under water?  I must—­know!”

“Good enough!  We’ll soon know, then,” replied Jacob Farnum.  He passed the word for Andrews, who came on deck.  The ventilators were quickly shipped.  Jack Benson shifted to the steersman’s seat inside the conning tower.  Sailing lights were turned off; the manhole cover was battened down securely.  They were dependent, now, on the air-compressing equipment whenever the air aboard became unfit to breathe.

Wedged on either side of Jack Benson in that little conning tower stood the builder and the inventor.

“You attend to the first submerging, Farnum,” begged the inventor.  “I—­I’m afraid I’m too nervous.”

The gasoline motor had just been shut off, the submarine now running at less speed under power from the electric motor.

Handling the controls in the conning tower, Mr. Farnum, not without a swift, shooting thrill of dread, opened the sea-valves to the water tanks.  As the tanks filled the “Pollard” settled lower and lower in the water.  They were beginning to go down.  All who were aboard felt the keen, apprehensive quiver of the thing, shut in, as they were, as though soldered inside a huge metal can.

The platform deck was quickly level with the water’s surface, though Jacob Farnum was not rushing things.  Then the deck outside, as shown by the steady glow of the lights in the conning tower, went out of sight, the water rising around the tower.

They continued slowly to sink until the top of the conning tower was less than three feet above the waves.

“Now, just a little dive!” pleaded David Pollard.  “Oh, merciful heaven!”

“Pass the word to brace yourselves for the dive!” bawled Mr. Farnum below, and Eph, stationed at the bottom of the spiral stairway, yelled the word to the engine room.

Now, the sea-valves of the forward diving tanks were opened.  As the water rushed into them, changing the balance of the boat, the bow shot downward, making it difficult for all to keep their footing.  It was as though they were sliding down an inclined plane.

Another lurch, and down they shot under the water, where men’s nerves may well be tried!

CHAPTER XI

THE TRY-OUT IN THE DEPTHS

Pollard clutched at the stairway railing with both hands, his face hard-set, his eyes staring.

He was not afraid.  In that supreme moment he could not know physical fear.  It was the inventor’s dread of failure that possessed him.

Jacob Farnum stood as one fascinated as he felt the boat plunging into the depths.

“Aren’t you going to put us on an even keel, sir?” Jack called.

The warning was needful.  In the exhilaration of that plunge Farnum was in danger of forgetting.