while tom and mr. damon continued on to atlantis after the oil, the young inventor lamenting from time to time that his remarks about the real destination of the advance had been overheard by mr. berg, the latter and his companion were hastening back along the path that ran on one side of the sand dunes.

"what's your hurry?" asked mr. maxwell, who was with the submarine agent. "you turned around as if you were shot when you saw that man and the lad. there didn't appear to be any cause for such a hurry. from what i could hear they were talking about a submarine. you're in the same business. you might be friends."

"yes, we might," admitted mr. berg with a peculiar smile; "but, unless i'm very much mistaken, we're going to be rivals."

"rivals? what do you mean?"

"i can't tell you now. perhaps i may later. but if you don't mind, walk a little faster, please. i want to get to a long-distance telephone."

"what for?"

"i have just overheard something that i wish to communicate to my employers, bentley & eagert."

"overheard something? i don't see what it could be, unless that lad—"

"you'll learn in good time," went on the submarine agent. "but i must telephone at once."

a little later the two men had reached a trolley line that ran into atlantis, and they arrived at the city before mr. damon and tom got there, as the latter had to go by a circuitous route. mr. berg lost no time in calling up his firm by telephone.

"i have had another talk with mr. swift," he reported to mr. bentley, who came to the instrument in philadelphia.

"well, what does he say?" was the impatient question. "i can't understand his not wanting to try for the government prize. it is astonishing. you said you were going to discover the reason, mr. berg, but you haven't done so."

"i have."

"what is it?"

"well, the reason mr. swift and his son don't care to try for the fifty thousand dollar prize is that they are after one of three hundred thousand dollars."

"three hundred thousand dollars!" cried mr. bentley. "what government is going to offer such a prize as that for submarines, when they are getting almost as common as airships? we ought to have a try for that ourselves. what government is it?"

"no government at all. but i think we ought to have a try for it, mr. bentley."

"explain."

"well, i have just learned, most accidentally, that the swifts are going after sunken treasure—three hundred thousand dollars in gold bullion."

"sunken treasure? where?

"i don't know exactly, but off the coast of uruguay," and mr. berg rapidly related what he had overheard tom tell mr. damon. mr. bentley was much excited and impatient for more details, but his agent could not give them to him.

"well," concluded the senior member of the firm of submarine boat builders, "if the swifts are going after treasure, so can we. come to philadelphia at once, mr. berg, and we'll talk this matter over. there is no time to lose. we can afford to forego the government prize for the chance of getting a much larger one. we have as much right to search for the sunken gold as the swifts have. come here at once, and we will make our plans."

"all right," agreed the agent with a smile as he hung up the receiver. "i guess," he murmured to himself, "that you won't be so high and mighty with me after this, tom swift. we'll see who has the best boat, after all. we'll have a contest and a competition, but not for a government prize. it will be for the sunken gold."

it was easy to see that mr. berg was much pleased with himself.

meanwhile, tom and mr. damon had reached atlantis, and had purchased the oil. they started back, but tom took a street leading toward the center of the place, instead of striking for the beach path, along which they had come.

"where are you going?" asked mr. damon.

"i want to see if that andy foger has come back here," replied the lad, and he told of having been shut in the tank by the bully.

"i've never properly punished him for that trick," he went on, "though we did manage to burst his auto tires. i'm curious to know how he knew enough to turn that gear and shut the tank door. he must have been loitering near the shop, seen me go in the submarine alone, watched his chance and sneaked in after me. but i'd like to get a complete explanation, and if i once got hold of andy i could make him talk," and tom clenched his fist in a manner that augured no good for the squint-eyed lad. "he was stopping at the same hotel with mr. berg, and he hurried away after the trick he played on me. i next saw him in shopton, but i thought perhaps he might have come back here. i'm going to inquire at the hotel," he added.

andy's name was not on the register since his hasty flight, however, and tom, after inquiring from the clerk and learning that mr. berg was still a guest at the hostelry, rejoined mr. damon.

"bless my hat!" exclaimed that eccentric individual as they started back to the lonely beach where the submarine was awaiting her advent into the water. "the more i think of the trip i'm going to take, the more i like it."

"i hope you will," remarked tom. "it will be a new experience for all of us. there's only one thing worrying me, and that is about mr. berg having overheard what i said."

"oh, don't worry about that. can't we slip away and leave no trace in the water?"

"i hope so, but i must tell dad and mr. sharp about what happened."

the aged inventor was not a little alarmed at what his son related, but he agreed with mr. damon, whom he heartily welcomed, that little was to be apprehended from berg and his employers.

"they know we're after a sunken wreck, but that's all they do know," said tom's father. "we are only waiting for the arrival of captain alden weston, and then we will go. even if bentley & eagert make a try for the treasure we'll have the start of them, and this will be a case of first come, first served. don't worry, tom. i'm glad you're going, mr. damon. come, i will show you our submarine."

as father and son, with their guest, were going to the machine shop, mr. sharp met them. he had a letter in his hand.

"good news!" the balloonist cried. "captain weston will be with us to-morrow. he will arrive at the beach hotel in atlantis, and wants one of us to meet him there. he has considerable information about the wreck."

"the beach hotel," murmured tom. "that is where mr. berg is stopping. i hope he doesn't worm any of our secret from captain weston," and it was with a feeling of uneasiness that the young inventor continued after his father and mr. damon to where the submarine was.