Chapter XV. The Airship Clue
 

"Now Ned, we'll try again. I'm going to use a still stronger current, and this is the most sensitive selenium plate I've turned out yet. We'll see if we can't get a better likeness of you--one that will be plainer."

It was Tom Swift who was speaking, and he and his chum had just completed some hard work on the new photo telephone. Though the apparatus did what Tom had claimed for it, still he was far from satisfied. He could transmit over the wire the picture of a person talking at the telephone, but the likeness was too faint to make the apparatus commercially profitable.

"It's like the first moving pictures," said Tom. "They moved, but that was about all they did."

"I say," remarked Ned, as he was about to take his place in the booth where the telephone and apparatus were located, "this double-strength electrical current you're speaking of won't shock me; will it? I don't want what happened to Eradicate to happen to me, Tom."

"Don't worry. Nothing will happen. The trouble with Rad was that he didn't have the wires insulated when he turned that arc current switch by mistake--or, rather, to play his joke. But he's all right now."

"Yes, but I'm not going to take any chances," insisted Ned. "I want to be insulated myself."

"I'll see to that," promised Tom. "Now get to your booth."

For the purpose of experiments Tom had strung a new line between two of his shops, They were both within sight, and the line was not very long; but, as I have said, Tom knew that if his apparatus would work over a short distance, it would also be successful over a long one, provided he could maintain the proper force of current, which he was sure could be accomplished.

"And if they can send pictures from Monte Carlo to Paris I can do the same," declared Tom, though his system of photo telephony was different from sending by a telegraph system--a reproduction of a picture on a copper plate. Tom's apparatus transmitted the likeness of the living person.

It took some little time for the young inventor, and Ned working with him, to fix up the new wires and switch on the current. But at last it was complete, and Ned took his place at one telephone, with the two sensitive plates before him. Tom did the same, and they proceeded to talk over the wire, first making sure that the vocal connection was perfect.

"All ready now, Ned! We'll try it," called Tom to his chum, over the wire. "Look straight at the plate. I want to get your image first, and then I'll send mine, if it's a success,"

Ned did as requested, and in a few minutes he could hear Tom exclaim, joyfully:

"It's better, Ned! It's coming out real clear. I can see you almost as plainly as if you were right in the booth with me. But turn on your light a little stronger."

Tom could hear, through the telephone, his chum moving about, and then he caught a startled exclamation.

"What's the matter?" asked Tom anxiously.

"I got a shock!" cried Ned. "I thought you said you had this thing fixed. Great Scott, Tom! It nearly yanked the arm off me! Is this a joke?"

"No, old man. No, of course not! Something must be wrong. I didn't mean that. Wait, I'll take a look. Say, it does seem as if everything was going wrong with this invention. But I'm on the right track, and soon I'll have it all right. Wait a second. I'll be right over."

Tom found that it was only a simple displacement of a wire that had given Ned a shock, and he soon had this remedied.

"Now we'll try again," he said. This time nothing wrong occurred, and soon Tom saw the clearest image he had yet observed on his telephone photo plate.

"Switch me on now, Ned," he called to his chum, and Ned reported that he could see Tom very plainly.

"So far--so good," observed Tom, as he came from the booth. "But there are several things I want yet to do."

"Such as what?" questioned Ned.

"Well, I want to arrange to have two kinds of pictures come over the wire. I want it so that a person can go into a booth, call up a friend, and then switch on the picture plate, so he can see his friend as well as talk to him. I want this plate to be like a mirror, so that any number of images can be made to appear on it. In that way it can be used over and over again. In fact it will be exactly like a mirror, or a telescope. No matter how far two persons may be apart they can both see and talk to one another."

"That's a big contract, Tom."

"Yes, but you've seen that it can be done. Then another thing I want to do is to have it arranged so that I can make a photograph of a person over a wire."

"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.