“This is a wonderful set which Mr. Grosvenor has had installed for us—isn’t he a prince, Una’s father—but not quite powerful enough to talk with him overseas.... We ought all to learn to use it perfectly—just to thank him!”
Patiently she began to “handle” her recent message, or the method of it, all over again, going from switch to switch, throwing the two-bladed aërial switch to one side to send, to the other to listen.
“It’s a ‘slow-thumbed’ business; one has to be careful of one’s bulbs, so that they’ll live long.” She was turning the rheostat knob, to light those bulbs—having re-started her generator, with its powerful current—moving that rheostat knob very gently, as when she had called “1—V. Z. M.” her father’s distant laboratory station, so that those shining vacuum tubes glowed slowly from dim to bright—with an incandescent eloquence that sent its poetry right into the enchained girls’ souls.
She was glancing at ammeters and radiation meter, the first to see if she was forcing those shining tubes too much, the second to determine whether she was putting enough power into the antennæ running around the raftered ceiling of the log cabin, above her.
“But explain it to us—more—Pemrose; how the message goes out! I’m beginning to love the radio shack—this shack side of the cabin,” cried various voices in tuneful keys and different pleading words.
“‘How it goes out!’” The inventor’s daughter wrinkled her brows, trying to meet the tax levied upon her—her matchless inheritance. “Well! father explained it first to me with the hackneyed illustration of throwing a stone into a pond, showing how the waves spread out, at first strong, growing weaker—and how they may be intercepted in various ways; so it is with the radio sound-waves. He illustrated it in the laboratory, too, with a pair of tuning forks, how if one is struck, the other, if it is in tune, will echo the sound at a little distance. If they are not in tune, there must be a magnet between, for them to vibrate, answer each other, with a funny, ‘surgy’ sound; we’ve tried it—”
“Oh! but tuning forks are an old song; and that does not tell all the story about radio. Go on—it’s fascinating.” Dorothy picked up the microphone from the table against the log wall.
“Well! when your voice goes into that it passes along the wire connecting it with the transmitter at the rate of a few hundred vibrations a second.” The girlish radio fan touched the two-foot cabinet containing the sending set. “But that is not speed enough to send a message out into the air, so my blessed Dad says—strength depends upon the rapidity of the vibrations, so the voice passes into this incandescent tube—bulb—where the vibrations are increased, but still not enough to send them out. But they pass on into this other vacuum tube, called the oscillator, where the vibrations are a thousand—and more—a second.”
“Whe-ew!” It was a prolonged whistle-whistle of awe.
“But that, again, would be too high frequency—beyond audibility. But, somehow, the shining bulbs strike an average between them—Dad says it’s a sort of grab game—between them—very difficult for any but the Wizard to understand,” Pem’s black eyebrows went merrily up. “But they do hit it off and the voice goes out into the ether in audio-frequency waves; waves that can be picked up—heard—on the back of an electric carrier wave.”