At last all had passed down the iron staircase save Eph, who remained by the wheel in the conning tower.

“Pass directly aft, everybody, please,” called Jack, quietly.

“What’s that for?” asked Miss Peddensen.

“We cannot allow anyone except naval officers to see how our diving apparatus is worked”, replied Jack.  “Some of you step into the staterooms, on either side, please.  All of the visitors must be aft of this curtain.”

The extreme after end of the cabin had been rigged with a heavy curtain that could be dropped into place.

“Why, I feel as if we were all being penned up here and held for the slaughter,” gasped one American girl, in a tone of fright.

“Yes, indeed!” protested Miss Peddensen.  “This is going too far.”

“It strikes me as being a good deal like an outrage,” blurted the young Englishman.  “Mr. Kimball, can’t you—­won’t you interfere in this matter?”

“I am very sorry,” replied the lieutenant commander, “but I cannot.  This step is necessary, in order to prevent anyone from having an improper view of the working of the craft.  I am going behind the curtain with you.  Mr. Featherstone will remain out in the cabin to aid in the handling of the boat.  You need none of you feel any uneasiness.”

Both Miss Peddensen and the Englishman ceased their objections.  But Jack, remembering the glance that had passed between the pair on deck, remained behind the curtain, too, as he dropped it.

“Go ahead, Hal!” he called.  “Fifty feet under the surface.  Dive gently.”

“O-o-o-oh!” came in little screams of alarm as the guests felt the floor on which they stood inclining at a sloping angle.

“We’re going below the surface now,” young Benson informed them.  “We’ll soon be running on an even keel.”

“All below,” called Hal Hastings in a few moments.

“And all clear?” asked Jack.

“All clear, Captain.”

“Jack Benson threw aside the heavy curtain, come forward, slowly ladies and gentlemen, and take seats,” was Jack’s invitation.  “I am sorry I shall have to ask you all to remain seated, but we cannot have any serious shifting of weight while we are running under the water.”

Though Eph was at the tower wheel Hal Hastings was now virtually in command of the boat, by previous arrangement, for young Benson meant to keep a sharp, though covert, eye on passengers.

The young skipper noted, swiftly, that Miss Peddensen had taken the seat furthest aft in the cabin, while the young Englishman was seated at the forward end of the party of guests.

“Oh, I say, Captain Benson,” called the Englishman, “are you permitted to show me how you know just how far below the surface you are?”

“The gauge tells that,” replied Jack.  “But I will ask you to excuse me from describing it, as I wish to keep my mind on the running of the boat.  Mr. Hastings will oblige you; or, I don’t doubt, one of the naval officers will.”