When Ned Newton got back to where Tom sat in the small telephone booth, the young banker found his chum staring rather moodily at the polished metal plate on the shelf that held the talking instrument.

"So it was no go; eh, Tom?"

"No go at all, Ned, and I thought sure I had it right this time."

"Then this isn't your first experiment?"

"Land no! I've been at it, off and on, for over a month, and I can't seem to get any farther. I'm up against a snag now, good and hard."

"Then there wasn't any image on your plate?"

"Not a thing, Ned. I don't suppose you caught any glimpse of me in your plate?" asked Tom, half hopefully.

"No. I couldn't see a thing. So you are going to try and make this thing work both ways, are you?"

"That's my intention, But I can fix it so that a person can control the apparatus at his end, and only see the person he is talking to, not being seen himself, unless he wishes it. That is, I hope to do that. Just now nobody can see anybody," and Tom sighed.

"Give it up," advised Ned. "It's too hard a nut to crack, Tom!"

"Indeed, I'll not give it up, Ned! I'm going to work along a new line. I must try a different solution of selenium on the metal plate. Perhaps I may have to try using a sensitized plate, and develop it later, though I do want to get the machine down so you can see a perfect image without the need of developing. And I will, too!" cried Tom. "I'll get some new selenium."

Eradicate, who came into the shop just then, heard the end of Tom's remarks. A strange look came over his honest black face, and he exclaimed:

"What all am dat, Massa Tom? Yo'ah gwine t' bring de new millenium heah? Dat's de end of de world, ain't it-dat millenium? Golly! Dish yeah coon neber 'spected t' lib t' see dat. De millenium! Oh mah landy!"

"No, Rad!" laughed Tom. "I was speaking about selenium, a sort of metallic combination that is a peculiar conductor of electricity. The more light that shines on it the better conductor it is, and the less light, the poorer."

"It must be queer stuff," said Ned.

"It is," declared Tom. "I think it is the only thing to use in this photo telephone experiment, though I might try the metal plate method, as they did between Monte Carlo and Paris. But I am not trying to make newspaper pictures."

"What is selenium, anyhow?" asked Ned. "Remember, Tom, I'm not up on this scientific stuff as you are."

"Selenium," went on Tom, "was discovered in 1817, by J. J. Berzelius, and he gave it that name from the Greek word for moon, on account of selenium being so similar, in some ways, to tellurium. That last is named after the Latin word tellus, the earth."

"Do they dig it?" Ned wanted to know.

"Well, sometimes selenium is found in combination with metals, in the form of selenides, the more important minerals of that kind being eucharite, crooksite, clausthalite, naumannite and zorgite--"

"Good night!" interrupted Ned, with a laugh, holding up his hands. "Stop it, Tom!" he pleaded. "You'll give me a headache with all those big words."

"Oh, they're easy, once you get used to them," said the young inventor, with a smile. "Perhaps it will be easier if I say that sometimes selenium is found in native sulphur. Selenium is usually obtained from the flue-dust or chamber deposits of some factory where sulphuric acid is made. They take this dust and treat it with acids until they get the pure selenium. Sometimes selenium comes in crystal forms, and again it is combined with various metals for different uses."

"There's one good thing about it. There are several varieties, and I'll try them all before I give up."

"That's the way to talk!" cried Ned. "Never say die! Don't give up the ship, and all that. But, Tom, what you need now is a little fun. You've been poking away at this too long. Come on out on the lake, and have a ride in the motor boat. It will do you good. It will do me good. I'm a bit rusty myself--been working hard lately. Come on--let's go out on the lake."

"I believe I will!" exclaimed Tom, after thinking it over for a moment. "I need a little fresh air. Sitting in that telephone booth, trying to get an image on a plate, and not succeeding, has gotten on my nerves. I want to write out an order for Koku to take to town, though. I want to get some fresh selenium, and then I'm going to make new plates."

Tom made some memoranda, and then, giving Koku the order for the chemist, the young inventor closed up his shop, and went with Ned down to Lake Carlopa, where the motor boat was moored.

This was not the same boat Tom had first purchased, some years ago, but a comparatively new and powerful craft.

"It sure is one grand little day for a ride," remarked Ned, as he got in the craft, while Tom looked over the engine.

"Yes, I'm glad you came over, and routed me out," said the young inventor. "When I get going on a thing I don't know enough to stop. Oh, I forgot something!"

"What?" asked Ned.

"I forgot to leave word about Mr. Railing's airship. It's all fixed and ready for him, but I put on a new control, and I wanted to explain to him about it. He might not know how to work it. I left word with father, though, that if he came for it he must not try it until he had seen me. I guess it will be all right. I don't want to go back to the house now."

"No, it's too far," agreed Ned.

"I have it!" exclaimed Tom. "I'll telephone to dad from here, not to let Halling go up until I come back. He may not come for his machine; but, if he does, it's best to be on the safe side Ned."

"Oh, sure."

Accordingly, Tom 'phoned from his boat-house, and Mr. Swift promised to see the bird-man if he called. Then Ned and Tom gave themselves up to the delights of a trip on the water.

The Kilo, which name Tom had selected for his new craft, was a powerful boat, and comfortable. It swept on down the lake, and many other persons, in their pleasure craft, turned to look at Tom's fine one.

"Lots of folks out to-day," observed Ned, as they went around a point of the shore.

"Yes, quite a number," agreed Tom, leaning forward to adjust the motor. "I wonder what's got into her?" he said, in some annoyance, as he made various adjustments. "One of the cylinders is missing."

"Maybe it needs a new spark plug," suggested Ned.

"Maybe. Guess I'll stop and put one in."

Tom slowed down the motor, and headed his boat over toward shore, intending to tie up there for a while.

As he shifted the wheel he heard a cry behind him, and at the same time a hoarse, domineering voice called out:

"Here, what do you mean, changing your course that way? Look out, or I'll run you down! Get out of my way, you land-lubber, you!"

Startled, Ned and Tom turned. They saw, rushing up on them from astern, a powerful red motor boat, at the wheel of which sat a stout man, with a very florid face and a commanding air.

"Get out of my way!" he cried. "I can't stop so short! Look out, or I'll run you down!"

Tom, with a fierce feeling of resentment at the fellow, was about to shift the course of the Kilo, but he was too late.

A moment later there came a smashing blow on the stern port quarter and the Kilo heeled over at a dangerous angle, while, with a rending, splintering sound of wood, the big red motorboat swept on past Tom and Ned, her rubstreak grinding along the side of the Kilo.