closed over the deck and the rounded
back of the boat. Had any one been watching they would have imagined
that an accident was taking place.

In the pilot house, with its thick glass windows, Tom, his father and
Captain Weston looked over the surface of the ocean, which every minute
was coming nearer and nearer to them.

"We'll be all under in a few seconds," spoke Tom in a solemn voice, as
he listened to the water hissing into the tanks.

"Yes, and then we can see what sort of progress we will make," added
Mr. Swift. "Everything is going fine, though," he went on cheerfully.
"I believe I have a good boat."

"There is no doubt of it in my mind," remarked Captain Weston, and Tom
felt a little disappointed that the sailor did not shout out some such
expression as "Shiver my timbers!" or "Keel-haul the main braces,
there, you lubber!" But Captain Weston was not that kind of a sailor,
though his usually quiet demeanor could be quickly dropped on
necessity, as Tom learned later.

A few minutes more and the waters closed over the top of the conning
tower. The Advance was completely submerged. Through the thick glass
windows of the pilot house the occupants looked out into the greenish
water that swirled about them; but it could not enter. Then, as the
boat went lower, the light from above gradually died out, and the
semi-darkness gave place to gloom.

"Turn on the electrics and the searchlight, Tom," directed his father.

There was the click of a switch, and the conning tower was flooded with
light. But as this had the effect of preventing the three from peering
out into the water, just as one in a lighted room cannot look out into
the night, Tom shut them off and switched on the great searchlight.
This projected its powerful beams straight ahead and there, under the
ocean, was a pathway of illumination for the treasure-seekers.

"Fine!" cried Captain Weston, with more enthusiasm than he had yet
manifested. "That's great, if you don't mind me mentioning it. How deep
are we?"

Tom glanced at a gage on the side of the pilot tower.

"Only about sixty feet," he answered.

"Then don't go any deeper!" cried the captain hastily. "I know these
waters around here, and that's about all the depth you've got. You'll
be on the bottom in a minute."

"I intend to get on the bottom after a while," said Mr. Swift, "but not
here. I want to try for a greater distance under water before I come to
rest on the ocean's bed. But I th