The Advance was made with a triple hull, the spaces between the layers of plates being filled with a secret material, capable of withstanding enormous pressure, as were also the plates themselves. Mr. Swift, aided by Mr. Jackson and Captain Weston, made a thorough examination, and found that not a drop of water had leaked in, nor was there the least sign that any of the plates had given way under the terrific strain.
"She's as tight as a drum, if you will allow me to make that comparison," remarked Captain Weston modestly. "I couldn't ask for a dryer ship."
"Well, let's take a look around by means the searchlight and the observation windows, and then we'll go back," suggested Mr. Swift. "It will take about two days to get the stores and provisions aboard and rig up the diving suits; then we will start for the sunken treasure."
There were several powerful searchlights on the Advance, so arranged that the bow, stern or either side could be illuminated independently. There were also observation windows near each light.
In turn the powerful rays were cast first at the bow and then aft. In the gleams could be seen the sandy bed of the ocean, covered with shells of various kinds. Great crabs walked around on their long, jointed legs, and Tom saw some lobsters that would have brought joy to the heart of a fisherman.
"Look at the big fish!" cried Mr. Damon suddenly, and he pointed to some dark, shadowy forms that swam up to the glass windows, evidently puzzled by the light.
"Porpoises," declared Captain Weston briefly, "a whole school of them."
The fish seemed suddenly to multiply, and soon those in the submarine felt curious tremors running through the whole craft.
"The fish are rubbing up against it," cried Tom. "They must think we came down here to allow them to scratch their backs on the steel plates."
For some time they remained on the bottom, watching the wonderful sight of the fishes that swam all about them.