But suddenly there came a startling interruption to the experiments.

Jack felt a sharp “Bang” at his ears as if a small cannon had been fired close at hand.

CHAPTER VIII.

Talking through space.

As the distance increased between air and land stations, the currents became stronger, and frequent tuning was necessary.  But Jack was able to keep up a constant conversation with his father, telling him all the details of the country as they flew along.  The sudden explosion, however, for it sounded like nothing else, startled him into a sharp exclamation.

“What in the world was that?”

As if he had spoken the question to someone close at hand, came back the explanation.

“Wireless telegraph wave crossing ours,” said his father.  “Some powerful land station is sending out a message, possibly to some ship.”

“It almost broke my ear drum,” said Jack, and inwardly resolved to devote some time to trying to solve the problem of avoiding such “collisions” in the future.  It occurred to him that some sort of a circuit breaker might be devised to cut off, temporarily, the telephone talk by automatic means when a cross-wave of high energy struck its current.

The shock was not repeated, and the conversation went on, still as sharp and as clear as when they had started out.  A few minutes later Jack was able to report they were passing over Rayburn.

“You’d better keep on,” said his father, his voice aglow with enthusiasm.  “It’s working beyond my wildest expectations.”

“It’s dandy,” agreed Jack.

They talked without raising their voices to any great extent, but it was necessary to articulate very clearly so that each variation of sound might be sent out into space as clearly as the notes of a singer come from the record of a phonograph.  But it was amazing, almost uncanny to Jack that such results could be obtained at all.

“Goodness, if only we could get that mineral substance that dad was talking about I believe you could rig up a radio telephone that would talk across the ocean,” he said to Tom, “and think what that would mean.  For instance, instead of bothering with the cable you could step into a radio-telephone office and say:  ‘Give me the London Exchange.’  In a few minutes the central would answer and you could tell her what number you wanted on some regular wire line.  Before long you’d get it, and be talking to whoever you had called just as if they were twenty-five miles off instead of three thousand!”

“It seems like a dream,” said Tom.

“Not much of a dream about it.  All it needs is development.  We’ve proved to-day it can be done,” declared Jack, bubbling over with enthusiasm.

They flew over meadow land and pasture, farmhouses where tiny figures emerged from buildings and looked up at them, over rivers and railroads, and still the alternator spat and sparked and the messages between Jack and his father were interchanged in a steady stream.  Rayburn had been left behind.  They were now over a small town Jack believed to be Hempstead.