“But wait!” the Captain exclaimed. “I have still another guest.” He gave Joyce Mills a strange look, then he roared:
“Old Man, come out!”
Out stepped Newton Mills. Like a flash, his daughter was in his arms.
“And might I add,” said Grace Krowl, “that he is also the mysterious Whisperer of the air!”
“That,” said the Captain, “calls for a lot of explaining. Suppose we retire to the parlor?”
“There’s really nothing very mysterious about that whisper business,” said Newton Mills when they were all gathered about the fire. “I became interested in something they call narrow-casting. It’s one of the uses of the electric eye. You really talk down a beam of light.”
“Talk down a beam of light!” someone exclaimed.
“Surely.” He smiled. “It’s really very simple. You talk into a microphone. An instrument takes up the sound impulses of your voice and changes them to light impulses. These impulses may be sent down a beam of light a mile, ten, twenty, thirty miles. How far? No one knows.
“A very special reflector catches those light impulses. A mechanism containing an electric eye changes those light impulses back into sound impulses. And then you hear my voice thirty miles away.
“The wonderful part is, Captain—” He leaned forward eagerly. “Only a person with the proper mechanism in the line of that ray of light can hear them! Think of being able to sit in my high tower and send secret messages to a score of my fellow detectives, and never a crook listening in! I tell you it is going to be a great thing for crime hunters in the future!”