mr. swift hurried up on deck. he was accompanied by captain weston. at the sight of tom's father, mr. berg, who had been joined by two other men, called out:

"you see we also concluded to give up the trial for the government prize, mr. swift. we decided there was more money in something else. but we still will have a good chance to try the merits of our respective boats. we hurried and got ours fitted up almost as soon as you did yours, and i think we have the better craft."

"i don't care to enter into any competition with you," said mr. swift coldly.

"ah, but i'm afraid you'll have to, whether you want to or not," was the insolent reply.

"what's that? do you mean to force this matter upon me?"

"i'm afraid i'll have to—my employers and i, that is. you see, we managed to pick up your trail after you left the jersey coast, having an idea where you were bound, and we don't intend to lose you now."

"do you mean to follow us?" asked captain weston softly.

"well, you can put it that way if you like," answered one of the two men with mr. berg.

"i forbid it!" cried mr. swift hotly. "you have no right to sneak after us."

"i guess the ocean is free," continued the rascally agent.

"why do you persist in keeping after us?" inquired the aged inventor, thinking it well to ascertain, if possible, just how much the men knew.

"because we're after that treasure as well as you," was the bold reply. "you have no exclusive right to it. the sunken ship is awaiting the first comer, and whoever gets there first can take the gold from the wreck. we intend to be there first, but we'll be fair with you."

"fair? what do you mean?" demanded tom.

"this: we'll race you for it. the first one to arrive will have the right to search the wreck for the gold bullion. is that fair? do you agree to it?"

"we agree to nothing with you," interrupted captain weston, his usual diffident manner all gone. "i happen to be in partial command of this craft, and i warn you that if i find you interfering with us it won't be healthy for you. i'm not fond of fighting, but when i begin i don't like to stop," and he smiled grimly. "you'd better not follow us."

"we'll do as we please," shouted the third member of the trio on the deck of the other boat, which, as tom could see, was named the wonder. "we intend to get that gold if we can."

"all right. i've warned you," went on the sailor, and then, motioning to tom and his father to follow, he went below.

"well, what's to be done?" asked mr. swift when they were seated in the living-room, and had informed the others of the presence of the rival submarine.

"the only thing i see to do is to sneak away unobserved, go as deep as possible, and make all haste for the wreck," advised the captain. "they will depend on us, for they have evidently no chart of the wreck, though of course the general location of it may be known to them from reading the papers. i hoped i had thrown them off the track by the false chart i dropped, but it seems they were too smart for us."

"have they a right to follow us?" asked tom.

"legally, but not morally. we can't prevent them, i'm afraid. the only thing to do is to get there ahead of them. it will be a race for the sunken treasure, and we must get there first."

"what do you propose doing, captain?" asked mr. damon. "bless my shirt-studs, but can't we pull their ship up on the island and leave it there?"

"i'm afraid such high-handed proceedings would hardly answer," replied mr. swift. "no, as captain weston says, we must get there ahead of them. what do you think will be the best scheme, captain?"

"well, there's no need for us to forego our plan to get fresh water. suppose we 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 could hear the electric siren of the wonder as it was blown to let them know that their escape had been noticed. a moment later the water, which acted as a sort of sounding-board, or telephone, brought to the ears of tom swift and his friends the noise of the engines of the other craft in operation. she was coming after them. the race for the possession of three hundred thousand dollars in gold was already under way. fate seemed against those on board the advance.