This was done by regulating the water in the tanks to the pressure at the depth it was desired to navigate. The delicate mechanisms designed to show depth, pressure, air value, and all the important details of a submarine were absolutely perfect.

So the three boys entered the water chamber, leaving Jimmie grinning through the glass panel. When the boat was brought to the bottom they opened the outer door and stepped out.

The Sea Lion had traversed only a short distance, yet the surface upon which the lads walked seemed very different from the smooth sand level Ned had seen before. There were now little ridges of sand, and now and then a pit opened up almost under their feet.

A dozen yards from where they emerged from the submarine they came upon the elevation which Ned had observed on his first trip out. It was not, however, a submerged rock or a bit of harder soil in the desert of sand. It was the hull of a wrecked vessel.

Ned moved along one side of the wreck, as far as his air-hose would permit him to go, and was satisfied that he had found the lost mail ship. The sand was already drifting against her sides, but she was still far from buried.

On the port side, about a third of the way to the stern from the bow, the boy discovered the wound which had brought the stately vessel to her present position. She lay, tilted about a quarter, in eighty feet of water.

Ned wondered why passing vessels had not discovered her. The tall stacks had been beaten down, probably snapped off at the collision, but the superstructure was high, and not far below the surface, Ned thought.

After motioning Jack and Frank to remain at the break in the side of the ship, Ned clambered up and, being careful to protect his air-hose and line from the jagged edges of the wound, crept inside. His electric flashlight revealed the interior only a short distance ahead of him, but at the very outset he saw that some of the air-tight compartments remained intact.

There was a lifting, swaying motion occasionally which told him that there was still air imprisoned in the broken ship. At that distance from the surface there would be no wave motion to produce the oscillations he observed.

"It is very strange," he mused, as he clambered over bales, chests and boxes in the hold, "that the ship should have gone down so quickly. Telegraphic reports at the time of the accident—if it was an accident—stated that she sank slowly. It would require only a little assistance to bring her to the surface."