"I just had the luck to get on a train coming home that had a car attached to it where they were trying out a new radio system," replied the minister. "I heard about it from the conductor, whom I know very well, and he arranged it so that I could go into the car where they were making the experiments. They had a radio set in there with a horn, and the set was connected with an aerial on the roof of the car. They sent out signals to various stations while the train was going along at the rate of forty miles an hour, and got replies that we could hear as plainly as though one of the people in the car were talking to the others. The whole thing was a complete success, and one of the officials of the road who happened to be in the party told me that the express trains on the road were going to be equipped with it.

"Of course, if one road does that, it will not be any time before all the others will, too. It'll not be long before we can be sitting in a car traveling, let us say from New York to Albany, and chat with a friend who may be on another train traveling between Chicago and Denver.

Or if a business man has started from New York to Chicago and happens to remember something important in his office he can call up his manager and give him directions just the same as though he pressed a buzzer and called him in from the next room."

"It sounds like magic," remarked Bob, drawing a long breath.

"If we'd even talked about such things a few hundred years ago we'd have been burned at the stake as wizards," laughed the doctor.

"The most important thing about this railroad development," he went on, "is not the convenience it may be in social and business life, but in the prevention of accidents. As it is now, after a train leaves a station it can't get any orders or information until it gets to the next station. A train may be coming toward it head on, or another train ahead of it and going in the same direction may be stalled. Often in the first case orders have come to the station agent to hold a train until another one has pa.s.sed. But the station agent gets the message just a minute too late, and the train has already left the station and is rushing on to its fate. Then all the agent can do is to shudder and wait for news of the crash. With the radio equipment he can call up the train, tell of the danger, and direct it to come back.

"Or take the second case where a train is stopped by some accident and knows that another train is coming behind it on the same track and is due in a few minutes. All they can do now is to send back a man with a red flag to stop the second train. But it may be foggy or dark, and the engineer of the second train doesn't see the flags and comes plunging on into the first train. With the radio, the instant a train is halted for any reason, it can send a message to the second train telling just where it is and warning of the danger. Hundreds have been killed and millions of dollars in property have been lost in the past just because of the old conditions. With the radio installed on trains, that sort of thing will be made almost impossible in the future.

"But there," he said, with a smile, "I came up here to answer your questions, and I've been doing all the talking. Now just what is it you wanted to ask me about radio?"

CHAPTER VI-THE WONDERFUL TUBE

"It's about getting a vacuum tube," replied Bob, in answer to the doctor's question. "The crystal detector is all right when we use the ear pieces. But we got to thinking about a horn so that lots of people could enjoy the concerts at the same time, and we figured that the crystal wouldn't be quite good enough for that."

The doctor smiled genially.

"I knew you'd be wanting that sooner or later," he said. "It's the second natural step in radio development. While you were still getting familiar with the working of the wireless, the crystal would do very well. But there comes a time to all amateurs when they get to hankering after something that is undeniably better. And the vacuum tube is that thing."

"It seems funny to me that the vacuum tube could have any use in radio,"

put in Jimmy. "I never thought of it in any way but as being used for an electric light."

"Neither did lots of other people," replied the doctor, smiling. "Even Mr. Edison himself didn't realize what its possibilities were. He did, though, discover some very curious things about it. In fact, he made the first step that led to its use for radio. He put a plate in one of his lamps. The plate didn't touch the filament, but formed part of a circuit of its own with a current indicator attached. Then when he turned on the light and the filament began to glow, the needle of the indicator began to twitch. Since the filament and the plate weren't touching, the movement of the needle indicated that the electricity must have jumped the gap between the two. But this simply showed that an invisible connection was established between the filament and the plate and nothing more came of it at the time.

"Now, it's likely that even yet we shouldn't have had that discovery of Edison's used for the development of radio if it hadn't been for the new theory of what electricity really is. That theory is that everything is electricity. This chair I'm sitting on, the railing to this porch, the hat that Jimmy is holding in his hand-all that is electricity."

Jimmy gave a little jump at this, and held his hat rather gingerly at arm's length and looked at it suspiciously.

The doctor joined in the laugh that followed.

"Oh, you needn't be afraid that you'll get a shock," he said.

"Electricity won't hurt you as long as it's at rest. It's only when it gets stirred up that high jinks are apt to follow."

Jimmy looked relieved.

"Now," continued the doctor, "the theory is that all matter is composed of an infinite number of electrons. An electron is the smallest thing that can be conceived, smaller even than the atom which used to be thought of as the unit. There may be millions, billions, quadrillions of them in a thing as big as a hickory nut. And when these electrons get busy you can look out for things to happen.

"Every hot object sends out electrons. That's the reason that the filament in the electric light tube sends them out."

"I suppose a red-hot stove would send them out, too," suggested Joe. "If that is so, I should think that people would have found out about them long ago."

"Ah, but there's this difference," explained the doctor. "The red-hot stove does send them out, but the air stops them. Remember that the atoms of which the air is composed are so large that the poor little electrons have no chance against them. It's like a baby pushing against a giant. It can't get by.

"Now the vacuum tube comes along, knocks out the giant of the air, and lets the baby electrons pet past him. The air is pumped out of the tube and the electrons have nothing to stop them. That's why Mr. Edison saw the needle on the plate begin to move, although the plate wasn't touching the filament. The electrons jumped across the gap between the filament and the plate because there was nothing to stop them.

"With this discovery of Mr. Edison's to aid him, a man named Fleming came along, who found that the oscillations caused by the flow of electrons to the plate could be utilized for the telephone by the use of what he called an oscillation valve that permitted the pa.s.sage of the current in one direction only. That was the second important step.

"But these two steps alone wouldn't have made radio what it is to-day if it hadn't been for the wonderful improvement made by DeForest. He mounted a grid of wire between the filament and the plate connected with a battery. He found that the slightest change in the current to the grid made a wonderfully powerful increase in the current that pa.s.sed from the filament to the plate. Just as when you touch the trigger of a rifle you have a loud explosion, so the grid magnifies tremendously the sound that would otherwise be weak or only ordinary. And by adding one vacuum valve to another the sound can be still further magnified until the crawling of a fly will sound like the tread of an elephant, until a mere whisper can become a crash of thunder, until the ticking of a watch will remind you of the din of a boiler factory, and the sighing of the wind through the trees on a summer night will be like the roar of Niagara.

"But there," he broke off, with a little laugh, "I'm letting my enthusiasm carry me away. It's hard to keep calm and cold-blooded when I get to talking about radio."

"Well, you don't care to talk about it more than we care to hear about it, you can be sure of that," said Joe warmly.

"Yes," chimed in Jimmy, "to me it's more interesting than a-a pirate story," he added rather lamely.

"With the advantage," laughed Dr. Dale, "that the pirate story usually has lots of pain and misery in it for somebody, while the radio has nothing but benefit for everybody. Why, you can scarcely think of any experience in which the radio won't help. Take an Arctic expedition for instance. It used to be that when a ship once disappeared in the ice floes of the Arctic regions it was lost to the world for years. n.o.body knew whether the explorers were alive or dead, were failing or succeeding, were safe and snug on board their ship or were shipwrecked and freezing on some field of ice. Look at the Greeley expedition, when for months the men were freezing and starving to death. If they had had a radio outfit with them, they could have communicated with the outside world, told all about their plight, given the exact place they were in, and help would have gone to them at once. Not a man need have perished.

So if a crew were shipwrecked on a desert island, they wouldn't to-day have to depend on a flag or bonfire to catch the attention of some ship that might just happen to be pa.s.sing near the island. All they would have to do would be to send out a radio message-provided, of course, they had one from the wrecked ship's stores or had material to make one-and a dozen vessels would go hurrying toward them. Those naval balloonists that were lost in the wilds of Canada a couple of years ago, that other expedition that perished in the heart of Labrador, and similar cases that might be counted by the dozens-all could have been helped if they had been able to tell their troubles to the outside world. I tell you, boys, we haven't half begun to realize what the discovery of radio means to the world.

"Now all this leads us back to vacuum tubes, for it's only with them that all these things would be possible. Perhaps in the future something better yet will be invented, but they're the best we have at present.

I'm heartily in favor of you boys using a tube instead of a crystal, because it will give you vastly more enjoyment in your work. I wouldn't have more than one at the start, but later on it may be well to have more. I have a catalogue up at my house of the various makes and prices, and if you'll run up there any time I'll give it to you. At the same time I'll show you just how it's got to be inserted and attached. Maybe also I'll be able to help you in the making of the horn. I'll have to go now," he added, looking at his watch. "It's surprising how the time flies when we get on this subject. Good-bye, boys, and don't forget to drop in at the house whenever you can."

The radio boys watched the minister's straight, alert figure as he went rapidly up the street.

"Isn't he all to the good?" asked Bob admiringly.

"You bet he is!" agreed Jimmy emphatically, the others nodding their a.s.sent.

CHAPTER VII-BASEBALL BY WIRELESS

For the next week the radio boys worked like beavers. They had pored over the catalogue that, according to his promise, Dr. Dale had lent them, and, acting on his advice, had picked out a tube of well-known make that could be bought for a moderate price. They had had to send to New York for it, because Dave Sloc.u.m did not have just that kind in stock, and they were feverish with impatience until it arrived. In the period of waiting they pitched in and helped Jimmy with the horn, and even Herb became sufficiently infected by the energy of the others to turn to and do his share of the work.

The precious tube arrived on Sat.u.r.day morning, and Bob, who had ordered it, was gloating over it when the other boys came over to the house.

"It's come at last!" he cried exultantly, holding up the tube for their inspection.

There were exclamations of satisfaction as the others gathered round Bob and examined it.

"And it's come just in time to get a good christening," declared Joe.

"That is, if we can have everything ready by three o'clock this afternoon."

"What do you mean?" asked Bob.

"Why, I just read in the morning paper that the broadcasting station is going to send out the big baseball game between the Giants and the Pittsburghs at the Polo Grounds this afternoon," replied Joe. "They say that they're going to send out the game play by play, every ball pitched, every strike, every hit, every base stolen, every run scored, so that you can follow the game from the time the first man goes to the bat till the last man goes out in the ninth inning. What do you think of that?"

What they thought of it was evident from the chorus of jubilation that followed. All of them were ardent baseball fans, and in addition to that were good players themselves. Bob was pitcher and Joe first baseman on the High School nine, while Jimmy played a good game at short and Herb took care of the center field garden.

Naturally, with this love of the game, they were keenly interested in the championship races of the big major league ball teams and, during the season, followed the ups and downs of their favorites with the closest attention. That spring the race had been especially hot between the Giants and the Pittsburghs. Both had started out well, and the Giants had cleaned up the majority of games in the East, while the Pittsburghs had been cutting a big swath in the West.