“Why not,” demanded Captain Mentor.  “You don’t mean to say that you have been building a boat up there in your little shack, do you?”

“Not a boat,” replied Tom, “but I think I have a means of sending out a call for help!”

“Oh, Tom—­Mr. Swift—­how?” exclaimed Mrs. Nestor.  “Do you mean we can send a message to my Mary?”

“Well, not exactly to her,” answered the young inventor, though he wished that such a thing were possible.  “But I think I can summon help.”

“How?” demanded Mr. Hosbrook.  “Have you managed to discover some cable line running past the island, and have you tapped it?”

“Not exactly.” was Tom’s calm answer, “but I have succeeded, with the help of Mr. Damon and Mr. Fenwick, in building an apparatus that will send out wireless messages!”

“Wireless messages!” gasped the millionaire.  “Are you sure?”

“Wireless messages!” exclaimed Mr. Jenks.  “I’ll give—­” He paused, clasped his hands on his belt, and turned away.

“Oh, Tom!” cried Mrs. Nestor, and she went up to the lad, threw her arms about his neck, and kissed him; whereat Tom blushed.

“Perhaps you’d better explain,” suggested Mr. Anderson.

“I will,” said the lad.  “That is the secret we have been engaged upon—­Mr. Damon, Mr. Fenwick and myself.  We did not want to say anything about it until we were sure we could succeed.”

“And are you sure now?” asked Captain Mentor.

“Fairly so.”

“How could you build a wireless station?” inquired Mr. Hosbrook.

“From the electrical machinery that was in the wrecked whizzer,” spoke Tom.  “Fortunately, that was not damaged by the shock of the fall, and I have managed to set up the gasolene engine, and attach the dynamo to it so that we can generate a powerful current.  We also have a fairly good storage battery, though that was slightly damaged by the fall.”

“I have just tested the machinery, and I think we can send out a strong enough message to carry at least a thousand miles.”

“Then that will reach some station, or some passing ship,” murmured Captain Mentor.  “There is a chance that we may be saved.”

“If it isn’t too late,” gloomily murmured the scientist.  “There is no telling when the island will disappear beneath the sea.”

But they were all so interested in Tom’s announcement that they paid little attention to this dire foreboding.

“Tell us about it,” suggested Mr. Nestor.  And Tom did.

He related how he had set up the dynamo and gasolene engine, and how, by means of the proper coils and other electrical apparatus, all of which, fortunately, was aboard the whizzer, he could produce a powerful spark.

“I had to make a key out of strips of brass, to produce the Morse characters,” the lad said.  “This took considerable time, but it works, though it is rather crude.  I can click out a message with it.”