"Well, I'll be blowed," exploded the captain, "if I didn't think you did it for a lark."

"There is one like it on the Marjorie," said Jim, who was using the binocular.

"Well, what do you think of that!" burst out the captain.

"What does it mean?" asked Tom.

"It means that someone on board is exchanging signals with the Marjorie," replied the professor.

"I wish I could catch them at it," muttered the captain, grimly.

"Let us take turns in watching," suggested Jim.

"I am going to do a little watching on my own account," growled the captain, making a dash for the supposed signal.

"Don't pull it down," advised the professor, "perhaps we can see who puts them up."

"I think you are right."

"They are doing some kind of signaling on the Marjorie now," went on Jim. "I can see some one waving a flag."

"There isn't anyone here who could see it," said the captain, looking over the deck. "Let me have a look," taking the gla.s.s. "There is some kind of signaling going on, but who can it be to?" Jo walked quietly to the stern of the boat, and leaning over the rail looked down. The stern windows of the cabin afforded a view of the pursuing vessel, and where the signals could be observed, but he could not see if anyone was there.

Something did attract his attention, however, though it only impressed itself on his mind as an odd chance. A keg was floating in the wake of the Storm King, but most unusual things are sometimes seen on the surface of the ocean, hundreds of miles from land.

"Perhaps there is someone in the cabin," he suggested, as he came back to where the captain was standing.

"By jove!" gasped the captain, making a dash for the companion way, "I believe you have it."

At this moment the steward came on deck.

"See here!" roared the captain, "What is the meaning of this?"

The steward smiled complacently, and said, "Why, sir, I know nothing about the flag. I have finished my tasks in the pantry, and came on deck for a breath of air."

The captain, debating the matter in his mind, concluded he would say no more at that time, and turned his attention again to the others. The steward went about his duties.

"They have quit signaling," reported Tom.

"What do you make of that other ship's continued interest in us, captain?" asked the professor.

"I'm blessed if I know," he replied. "It's too deep for me. They have been following us ever since we left the bay, and I'm blessed if I don't think they are after us. But I cannot imagine for what purpose."

"I suspect," said the professor, "that they have some knowledge of the fact that we are after a treasure."

"Oh," said the captain, "but they can't expect to keep us under observation for a long trip like this. It would be ridiculous."

"What they want most likely is the chart. Only with its aid can anyone locate the island or the treasure."

The captain sat for a few moments in thought. "There must have been somebody on board getting the signals. Now who could it be?"

"One of the crew," suggested Tom.

"Quite likely," agreed the captain, "unless--"

"What?" said the professor.

"It was the steward."

"No," said the professor. "You can leave him out. He has been with me for years."

"All the more reason," returned the captain. "He'll jolly well stand watching. What we have got to do is to watch out, and perhaps we can trap them."

"I think--" he added. With a sudden thought he got up and went to the companion way, returning slowly to his seat. "I may have a clue."

"What is it?" cried Tom.

"It is only an idea, don't you know, and I won't say anything until I work it out. You say the chart is aboard?"

"Yes."

The captain whistled softly for a minute. "Better put it away somewhere."

"That has already been done," admitted the professor, looking at the boys. "It is hidden away, and I don't think anyone can find it."

"Even if they could find it, how could they get away with it?" inquired Tom.

"That's easily done," explained the captain, "when they find it."

"When!" interrupted Tom.

"Maybe only a matter of days," returned the captain. "They will signal to the other ship, put it in a keg, drop it over and the others will pick it up."

"A keg," queried Jo. "I saw a keg floating in the wake of our ship just a little while ago."

CHAPTER XV.

THE CHART.

"Indeed! Then you had better investigate your hiding place and see if your chart is secure."

Jo acted immediately upon the suggestion, and went below. Closing the door of his room, he pressed the spring that should open the adjoining panel. It did not respond readily to the pressure of his hand. Evidently it had been tampered with. With feverish haste he tried again and again, and finally his efforts were rewarded with success. The door flew open.

The box was raised, but the chart was not within.