Tom Swift was so overjoyed and excited that for a few moments he capered about, inside the booth, and outside, knocking against his chum Ned, clapping him on the back, and doing all manner of boyish "stunts."

"It's a success, Ned! I've struck it!" cried Tom, in delight.

"Ouch! You struck me, you mean!" replied Ned, rubbing his shoulder, where the young inventor had imparted a resounding blow of joy.

"What of it?" exclaimed Tom. "My apparatus works! I can send a picture by telephone! It's great, Ned!"

"But I don't exactly understand how it happened," said Ned, in some bewilderment, as he gazed at the selenium plate.

"Neither do I," admitted Tom, when he had somewhat calmed down. "That is, I don't exactly understand what made the thing succeed now, when it wouldn't work for me a little while ago. But I've got to go into that. I'll have to interview that rascal Eradicate, and learn what he did when he played that trick on Koku. Yes, and I'll have to see Koku, too. We've got to get at the bottom of this, Ned."

"I suppose so. You've got your hands full, Tom, with your photo telephone, and the disappearance of Mr. Damon."

"Yes, and my own airship, too. I must get after that. Whew! A lot of things to do! But I like work, Ned. The more the better."

"Yes, that's like you, Tom. But what are you going to get at first?"

"Let me see; the telephone, I think. I'll have Rad and Koku in here and talk to them. I say, you Eradicate!" he called out of the door of the shop, as he saw the colored man going past, holding his shocked arm tenderly.

"Yas, sah, Massa Tom, I'se comin'! What is it yo' all wants, Massa Tom?"

"I want you to show me exactly what you did to the wires, and other things in here, when you played that Angel Gabriel trick on your partner Koku."

"Partner! He ain't mah partner!" exclaimed Eradicate with a scowl, for there was not the best of feeling between the two. Eradicate had served in the Swift family many years, and he rather resented the coming of the giant, who performed many services formerly the province of the colored man.

"Well, never mind what he is, Rad," laughed Tom. "You just show me what you did. Come now, something happened in here, and I want to find out what it was."

"Oh, suffin done happened all right, Massa Tom. Yas, sah! Suffin done happened!" cried Eradicate, with such odd emphasis that Tom and Ned both laughed.

"An' suffin happened to me," went on the colored man, rubbing his shocked arm.

"Well, tell us about it," suggested Tom.

"It was dish yeah way," proceeded Eradicate. And he told more in detail how, seeing Koku cleaning and sweeping out the other telephone booth, he had thought of the trick to play on him. Both telephones had what are called "amplifiers" attached, that could be switched on when needed. These amplifiers were somewhat like the horn of a phonograph--they increased, or magnified the sound, so that one could hear a voice from any part of the shop, and need not necessarily have the telephone receiver at his ear.

Seeing Koku near the instrument, Eradicate had switched on the amplifier, and had called into his instrument, trying to scare the giant. And he did startle Koku, for the loud voice, coming so suddenly, sent the giant out of the booth on the run.

"But you must have done something else," insisted Tom. "Look here, Rad," and the young inventor pointed to the picture on the plate.

"Mah gracious sakes!" gasped the colored man. "Why dat's Koku hisse'f!" and he looked in awe at the likeness.

"That's what you did, Rad!"

"Me? I done dat? No, sah, Massa Tom. I neber did! No, sah!" Eradicate spoke emphatically.

"Yes you did, Rad. You took that picture of Koku over my photo telephone, and I want you to show me exactly what you did--what wires and switches you touched and changed, and all that."

"Yo--yo' done say I tuck dat pishure, Massa Tom?"

"You sure did, Rad."

"Well--well, good land o' massy! An' I done dat!"

Eradicate stared in wonder at the image of the giant on the plate, and shook his head doubtingly.

"I--I didn't know I could do it. I never knowed I had it in me!" he murmured.

Tom and Ned laughed long and loud, and then the young inventor said:

"Now look here, Rad. You've done me a mighty big service, though you didn't know it, and I want to thank you. I'm sorry about your arm, and I'll have the doctor look at it. But now I want you to show me all the things you touched when you played that joke on Koku. In some way you did what I haven't been able to do, You took the picture. There's probably just one little thing I've overlooked, and you stumbled on it by accident. Now go ahead and show me."

Eradicate thought for a moment, and then said:

"Well, I done turned on de current, laik I seen you done, Massa Tom."

"Yes, go on. You connected the telephone."

"Yas, sah. Den I switched on that flyer thing yo' all has rigged up."

"You switched on the amplifier, yes. Go on."

"An'--an' den I plugged in dish year wire," and the colored man pointed to one near the top of the booth.

"You switched on that wire, Rad! Why, great Scott, man! That's connected to the arc light circuit--it carries over a thousand volts. And you switched that into the telephone circuit?"

"Dat's what I done did, Massa Tom; yas, Bah!"

"What for?"

"Why, I done want t' make mah voice good an' loud t' skeer dat rascal Koku!"

Tom stared at the colored man in amazement.

"No wonder you got a shock!" exclaimed the young inventor. "You didn't get all the thousand volts, for part of it was shunted off; but you got a good charge, all right. So that's what did the business; eh? It was the combination of the two electrical circuits that sent the photograph over the wire."

"I understand it now, Rad; but you did more than I've been able to do. I never, in a hundred years, would have thought of switching on that current. It never occurred to me. But you, doing it by accident, brought out the truth. It's often that way in discoveries. And Koku was standing in the other telephone booth, near the plate there, when you switched in this current, Rad?"

"Yas, sah, Massa Tom. He were. An' yo' ought t' see him hop when he heard mah voice yellin' at him. Ha! ha! ha!"

Eradicate chuckled at the thought. Then a pain in his shocked arm made him wince. A wry look passed over his face.

"Yas, sah, Koku done jump about ten feet," he said. "An'--an' den I jump too. Ain't no use in denyin' dat fact. I done jump when I got dat shock!"

"All right, Rad. You may go now. I think I'm on the right track!" exclaimed Tom. "Come on, Ned, we'll try some experiments, and we'll see what we can do."

"No shocks though--cut out the shocks, Tom," stipulated his chum.

"Oh, sure! No shocks! Now let's bet busy and improve on Eradicate's Angel Gabriel system."

Tom made a quick examination of the apparatus.

"I understand it, I think," he said. "Koku was near the plate in the other booth when Rad put on the double current. There was a light there, and in an instant his likeness was sent over the wire, and imprinted on this plate. Now let's see what we can do. You go to that other booth, Ned. I'll see if I can get your picture, and send you mine. Here, take some extra selenium plates along. You know how to connect them."

"I think so," answered Ned.

"This image is really too faint to be of much use," went on Tom, as he looked at the one of Koku. "I think I can improve on it. But we're on the right track."

A little later Ned stood in the other booth, while Tom arranged the wires, and made the connections in the way accidently discovered by Eradicate. The young inventor had put in a new plate, carefully putting away the one with the picture of the giant, This plate could be used again, when the film, into which the image was imprinted, had been washed off.

"All ready, Ned," called Tom, over the wire, when he was about to turn the switch. "Stand still, and I'll get you."

The connection was made, and Tom uttered a cry of joy. For there, staring at him from the plate in front of him was the face of Ned.

It was somewhat reduced in size, of course, and was not extra clear, but anyone who knew Ned could have told he was at the other end of the wire.

"Do you get me, Tom?" called Ned, over the telephone.

"I sure do! Now see if you can get me."

Tom made other connections, and then looked at the sending plate of his instrument, there being both a sending and receiving plate in each booth, just as there was a receiver and a transmitter to the telephone.

"Hurray! I see you, Tom!" cried Ned, over the wire. "Say, this is great!"

"It isn't as good as I want it," went on Tom. "But it proves that I'm right. The photo telephone is a fact, and now persons using the wire can be sure of the other person they are conversing with. I must tell dad. He wouldn't believe I could do it!"

And indeed Mr. Swift was surprised when Tom proved, by actual demonstration, that a picture could be sent over the wire.

"Tom, I congratulate you!" declared the aged inventor. "It is good news!"

"Yes, but we have bad news of Mr. Damon," said Tom, and he told his father of the disappearance of the eccentric man. Mr. Swift at once telephoned his sympathy to Mrs. Damon, and offered to do anything he could for her.

"But Tom can help you more than I can," he said. "You can depend on Tom."

"I know that," replied Mrs. Damon, over the wire.

And certainly Tom Swift had many things to do now. He hardly knew at what to begin first, but now, since he was on the right road in regard to his photo telephone, he would work at improving it.

And to this end he devoted himself, after he had sent out a general alarm to the police of nearby towns, in regard to the disappearance of Mr. Damon. The airship clue, he believed, as did the police, would be a good one to work on.

For several days after this nothing of moment occurred. Mr. Damon could not be located, and Tom's airship might still be sailing above the clouds as far as getting any trace of it was concerned.

Meanwhile the young inventor, with the help of Ned, who was given a leave of absence from the bank, worked hard to improve the photo telephone.