go to the island, that is, some of us, leaving a guard on
board here. We'll fill our tanks with fresh water, and at night we'll
quietly sink below the surface and speed away."

They all voted that an excellent idea, and little time was lost putting
it into operation.

All the remainder of that day not a sign of life was visible about the
Wonder. She lay inert on the surface of the lagoon, not far away from
the Advance; but, though no one showed himself on the deck, Tom and his
friends had no doubt but that their enemies were closely watching them.

As dusk settled down over The tropical sea, and as the shadows of the
trees on the little island lengthened, those on board the Advance
closed the Conning tower. No lights were turned on, as they did not
want their movements to be seen, but Tom, his father and Mr. Sharp took
their positions near the various machines and apparatus, ready to open
the tanks and let the submarine sink to the bottom, as soon as it was
possible to do this unobserved.

"Luckily there's no moon," remarked Captain Weston, as he took his
place beside Tom. "Once below the surface and we can defy them to find
us. It is odd how they traced us, but I suppose that steamer gave them
the clue."

It rapidly grew dark, as it always does in the tropics, and when a
cautious observation from the conning tower did not disclose the
outlines of the other boat, those aboard the Advance rightly concluded
that their rivals were unable to see them.

"Send her down, Tom," called his father, and with a hiss the water
entered the tanks. The submarine quickly sank below the surface, aided
by the deflecting rudder.

But alas for the hopes of the gold-seekers. No sooner was she
completely submerged, with the engine started so as to send her out of
the lagoon and to the open sea, than the waters all about were made
brilliant by the phosphorescent phenomenon. In southern waters this
frequently occurs. Millions of tiny creatures, which, it is said,
swarm in the warm currents, give an appearance of fire to the ocean,
and any object moving through it can plainly be seen. It was so with
the Advance. The motion she made in shooting forward, and the
undulations caused by her submersion, seemed to start into activity the
dormant phosphorus, and the submarine was afloat in a sea of fire.

"Quick!" cried Tom. "Speed her up! Maybe we can get out of this patch
of water before they see us."

But it was too late. Above them they