“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 passage 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 passed 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. Nobody 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 passing 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