“That may be,” said Mr. Hosbrook, who had been considering installing a wireless plant on his yacht, and who, therefore, knew something about it, “you may send a message, but can you receive an answer?”

“I have also provided for that,” replied Tom.  “I have made a receiving instrument, though that is even more crude than the sending plant, for it had to be delicately adjusted, and I did not have just the magnets, carbons, coherers and needles that I needed.  But I think it will work.”

“Did you have a telephone receiver to use?”

“Yes.  There was a small interior telephone arrangement on Mr. Fenwick’s airship, and part of that came in handy.  Oh, I think I can hear any messages that may come in answer to ours.”

“But what about the aerial wires for sending and receiving messages?” asked Mr. Nestor.

“Don’t you have to have several wires on a tall mast?”

“Yes, and that is the last thing to do,” declared Tom.  “I need all your help in putting up those wires.  That tall tree on the crest of the island will do,” and he pointed to a dead palm that towered gaunt and bare like a ship’s mast, on a pile of rocks in the centre of Earthquake Island.

CHAPTER XXI

MESSAGES INTO SPACE

Tom Swift’s announcement of the practical completion of his wireless plant brought hope to the discouraged hearts of the castaways.  They crowded about him, and asked all manner of questions.

Mr. Fenwick and Mr. Damon came in for their share of attention, for Tom said had it not been for the aid of his friends he never could have accomplished what he did.  Then they all trooped up to the little shack, and inspected the plant.

As the young inventor had said, it was necessarily crude, but when he set the gasolene motor going, and the dynamo whizzed and hummed, sending out great, violet-hued sparks, they were all convinced that the young inventor had accomplished wonders, considering the materials at his disposal.

“But it’s going to be no easy task to rig up the sending and receiving wires,” declared Tom.  “That will take some time.”

“Have you got the wire?” asked Mr. Jenks.

“I took it from the stays of the airship,” was Tom’s reply, and he recalled the day he was at that work, when the odd man had exhibited the handful of what he said were diamonds.  Tom wondered if they really were, and he speculated as to what might be the secret of Phantom Mountain, to which Mr. Jenks had referred.

But now followed a busy time for all.  Under the direction of the young inventor, they began to string the wires from the top of the dead tree, to a smaller one, some distance away, using five wires, set parallel, and attached to a wooden spreader, or stay.  The wires were then run to the dynamo, and the receiving coil, and the necessary ground wires were installed.