At the jail a watch was kept to see whether Gaston would have visitors, but none came.  M. Lemaire and Mlle. Nadiboff were known to be still at the hotel, but they did not go near their man in trouble.  Neither did Lemaire or the Russian appear about the grounds of the hotel.

At noon a letter from Lieutenant Commander Kimball came aboard the submarine, inquiring whether Captain Benson could make it convenient to take him and several officers out to sea afternoon and give an exhibition of the boat’s diving powers.

“After we’ve taken the boat out ourselves, and tested her,” was the answer Captain Jack sent back.  “With so many spies about we want to be sure that the boat is in safe running order before we risk the lives of half a dozen naval officers.”

A luncheon was eaten, after which, the young submarine captain hastily climbed the stairs to the conning tower.

“Throw on the gasoline, Hal,” he called back over his shoulder.  “And, as soon as we get way, test all the electric connections, before we attempt to do any diving.  Be sure of everything old fellow.”

Forward in the engine room the gas motors were soon moving merrily.  By the time that Eph had cast loose from moorings Jack signaled for slow speed ahead, and the grim-looking little Benson moved on out of the harbor.

Once out of the harbor Captain Jack rang, successively, for two higher speeds.  The “Benson” answered both like a charm.

“The gasoline part of the craft is working all right,” declared the youthful skipper to Eph, who had come up into the tower.

Fifteen minutes later Hal shouted up: 

“All electric connections appear safe, Captain.  And all the air compressors are working.”

“Are you ready to shut off the gasoline motors?”

“Yes, sir.”

“Go ahead, then, and we’ll take a dive.”  Down they shot below the surface, the boat going on a diving keel.  Then, for some minutes, Captain Jack ran his submarine pride along at a depth of fifty feet below surface.

“Might as well rise, Captain,” called up Mr. Farnum, coming from his stateroom.

So Eph, at the young commander’s orders, stood by to let the compressed air gradually into the water tanks.  As gracefully as ever the “Benson” rose to the surface.  Gasoline power was turned on again.

“Everything is all safe, Captain,” nodded Mr. Farnum.  “Run back and get your naval party.”

As they were to run, now, on the surface, Jack stepped out to stand by the deck wheel Eph and Hal came out with him, David Pollard standing further aft.

As the submarine rounded in under the gunboat’s stern the voice of Kimball called: 

“As well done as ever, Mr. Benson!  When shall we come on board?”

“As soon as we’re moored, sir,” Jack shouted

As the “Benson” ran to her moorings the youthful captain espied a shore boat that bore, as sole passenger, one of the uniformed, colored bell boys from the hotel.