r, 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 n