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 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.”
Конец ознакомительного фрагмента.
Текст предоставлен ООО «ЛитРес».
Прочитайте эту книгу целиком, купив полную легальную версию на ЛитРес.
Безопасно оплатить книгу можно банковской картой Visa, MasterCard, Maestro, со счета мобильного телефона, с платежного терминала, в салоне МТС или Связной, через PayPal, WebMoney, Яндекс.Деньги, QIWI Кошелек, бонусными картами или другим удобным Вам способом.
