“I fancy Captain Mentor can supply our longitude and latitude,” answered Tom.  “I will give that with every message I send out, and help may come—­some day.”

“It can’t come any too quick for me!” declared Mr. Damon.  “Bless my door knob, but my wife must be worrying about my absence!”

“What message for help will you send?” Captain Mentor wanted to know.

“I am going to use the old call for aid,” was the reply of the young inventor.  “I shall flash into space the three letters ‘C.Q.D.’  They stand for ‘Come Quick—­Danger.’  A new code call has been instituted for them, but I am going to rely on the old one, as, in this part of the world, the new one may not be so well understood.  Then I will follow that by giving our position in the ocean, as nearly as Captain Mentor can figure it out.  I will repeat this call at intervals until we get help—­”

“Or until the island sinks,” added the scientist, grimly.

“Here!  Don’t mention that any more,” ordered Mr. Hosbrook.  “It’s getting on my nerves!  We may be rescued before that awful calamity overtakes us.”

“I don’t believe so,” was Mr. Parker’s reply, and he actually seemed to derive pleasure from his gloomy prophecy.

“It’s lucky you understand wireless telegraphy, Tom Swift,” said Mr. Nestor admiringly, and the other joined in praising the young inventor, until, blushing, he hurried off to make some adjustments to his apparatus.

“Can you compute our longitude and latitude, Captain Mentor,” asked the millionaire yacht owner.

“I think so,” was the reply.  “Not very accurately, of course, for all my papers and instruments went down in the resolute.  But near enough for the purpose, I fancy.  I’ll get right to work at it, and let Mr. Swift have it.”

“I wish you would.  The sooner we begin calling for help the better.  I never expected to be in such a predicament as this, but it is wonderful how that young fellow worked out his plan of rescue.  I hope he succeeds.”

It took some little time for the commander to figure their position, and then it was only approximate.  But at length he handed Tom a piece of paper with the latitude and longitude written on it.

In the meanwhile, the young inventor had been connecting up his apparatus.  The wires were now all strung, and all that was necessary was to start the motor and dynamo.

A curious throng gathered about the little shack as Tom announced that he was about to flash into space the first message calling for help.  He took his place at the box, to which had been fastened the apparatus for clicking off the Morse letters.

“Well, here we go,” he said, with a smile.

His fingers clasped the rude key he had fashioned from bits of brass and hard rubber.  The motor was buzzing away, and the electric dynamo was purring like some big cat.

Just as Tom opened the circuit, to send the current into the instrument, there came an omnious rumbling of the earth.