"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 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
assent.