“Meaning what?”

“Meaning that if a certain person talks to me over the wire, I can turn my switch, and get a picture of him here at my apparatus connected with my telephone.  To do that I’ll merely need a sending apparatus at the other end of the telephone line—­not a receiving machine.”

“Could you arrange it so that the person who was talking to you would have his picture taken whether he wanted it or not?” asked Ned.

“Yes, it might be done,” spoke Tom, thoughtfully.  “I could conceal the sending plate somewhere in the telephone booth, and arrange the proper light, I suppose.”

“That might be a good way in which to catch a criminal,” went on Ned.  “Often crooks call up on the telephone, but they know they are safe.  The authorities can’t see them—­they can only hear them.  Now if you could get a photograph of them while they were telephoning—­”

“I see!” cried Tom, excitedly.  “That’s a great idea!  I’ll work on that, Ned.”

And, all enthusiasm, Tom began to plan new schemes with his photo telephone.

The young inventor did not forget his promise to help Mrs. Damon.  But he could get absolutely no clue to her husband’s whereabouts.  Mr. Damon had completely and mysteriously disappeared.  His fortune, too, seemed to have been swallowed up by the sharpers, though lawyers engaged by Tom could fasten no criminal acts on Mr. Peters, who indignantly denied that he had done anything unlawful.

If he had, he had done it in such a way that he could not be brought to justice.  The promoter was still about Shopton, as well groomed as ever, with his rose in his buttonhole, and wearing his silk hat.  He still speeded up and down Lake Carlopa in his powerful motor boat.  But he gave Tom Swift a wide berth.

Late one night, when Tom and Ned had been working at the new photo telephone, after all the rest of the household had retired, Tom suddenly looked up from his drawings and exclaimed: 

“What’s that?”

“What’s what?” inquired Ned.

“That sound?  Don’t you hear it?  Listen!”

“It’s an airship—­maybe yours coming back!” cried the young banker.

As he spoke Ned did hear, seemingly in the air above the house, a curious, throbbing, pulsating sound.

“That’s so!  It is an airship motor!” exclaimed Tom.  “Come on out!”

Together they rushed from the house, but, ere they reached the yard, the sound had ceased.  They looked up into the sky, but could see nothing, though the night was light from a full moon.

“I certainly heard it,” said Tom.

“So did I,” asserted Ned.  “But where is it now?”

They advanced toward the group of work-buildings.  Something showing white in the moonlight, before the hangar, caught Ned’s eyes.

“Look!” he exclaimed.  “There’s an airship, Tom!”

The two rushed over to the level landing place before the big shed.  And there, as if she had just been run out for a flight, was the Eagle.  She had come back in the night, as mysteriously as she had been taken away.