“Yes, it’s something lively that I’m thinking about,” laughed young Benson.

Over the supper table, that evening, Captain Jack announced the scheme that had entered his mind while listening to Lieutenant McCrea.

Jacob Farnum listened, at first, somewhat thunderstruck.  Then, of a sudden, he laid down his knife and fork, bursting into a roar of laughter.

“It sounds like a fearfully cheeky thing to do, I know,” confessed the young captain.

“It surely is,” confirmed David Pollard, nervously.

“Yet,” pursued young Benson, “if the trick should succeed, how it would take the conceit out of some people who don’t believe in submarines.”

“Wouldn’t it?” rejoined Mr. Farnum, his eyes twinkling with merriment.

“Yet you don’t intend to try it, do you?” asked the inventor.

“I don’t know,” confessed Mr. Farnum.  “But I’ll admit this much—­I’m certainly thinking hard over the scheme that Captain Benson has proposed.”

“It would be unfortunate if we did the thing, and only succeeded in offending the officers of the Navy,” pursued the inventor, an extremely thoughtful look on his pallid, thin face.

“Oh, of course, as far as the mere expense goes, I’d pay the bill for the trick,” Farnum went on.  “To tell the truth.  Dave, the point I’m considering most now is, whether we can really successfully play the trick that Captain Benson has sprung on us.”

“I believe we can; don’t believe there’ll be any difficulty whatever,” declared the young captain, his eyes glowing.

“Well, I’m going to think it over a while,” announced the builder, as he finished his meal.

He went directly up to the platform deck, seating himself on a folding chair.  From the loud chuckles that came, from time to time, from the platform deck, it was plain that the boatbuilder had had his sense of humor mightily tickled.

Presently, the hail came: 

“Benson, come up here, won’t you?”

As Jack reported to the builder Farnum stood looking across the bay.

“Captain, how are we going to get at the exact distance between our boat and the ’Luzon’?”

“It’s a question of mathematics, isn’t it?” asked Jack, slowly.  “Mr. Pollard is the expert in that line, isn’t he?”

“Oh, I say, Dave,” bawled the builder down the stairway.  “Come up here, won’t you?  Now, how far is it from our moorings to those of the ’Luzon’?”

There being still enough daylight for the purpose, Mr. Pollard brought up a small transit.  Measuring a base-line on the deck of the submarine, he took two observations, then went below to do some rapid figuring.

“Exactly 1,142 feet, from mooring to mooring,” he called up through the manhole, presently.

“If you’ve got the distance down as fine as that,” laughed back Mr. Farnum, “good enough!”

“Are you going to try to play Benson’s trick, then?” asked the inventor, reappearing on deck.