"A condenser speaker?"
"Sure, the gadget developed way back in the 1920s. It hasn't been used for years to my knowledge, but it might do the trick."
Russ grinned broadly. "Hell, why didn't I think of that? Here I've been racking my brain for a new approach, a new wrinkle ... and exactly what I wanted was at hand."
"Should work," declared Greg. "Just the opposite of a condenser microphone. Instead of radiating sound waves mechanically, it radiates a changing electric field and this field becomes audible directly within the ear. Even yet no one seems to understand just how it works, but it does ... and that's good enough."
"I know," said Russ. "It really makes no sound. In other words it creates an electric field that doubles for sound. It ought to be just the thing because nothing can stop it. Metal shielding can, I guess, if it's thick enough, but it's got to be pretty damn thick."
It took time to set the mechanism up. Ready, the massive apparatus, within which glowed a larger and more powerful force field, was operated by two monstrous material energy engines. The controls were equipped with clockwork drives, designed so that the motion of the Earth could be nullified completely and automatically for work upon outlying planets.
Russ stood back and looked at it. "Stand in front of that screen, Greg," he said, "and we'll try it on you."
Greg stepped in front of the screen. The purr of power came on. Suddenly, materializing out of the air, came Greg's projection. Hazy and undefined at first, it rapidly assumed apparent solidity. Greg waved his arm; the image moved its arm.
Russ left the controls and walked across the laboratory to inspect the image. Examined from all sides, it looked solid. Russ walked through it and felt nothing. There was nothing there. It was just a three-dimensional image. But even from two feet away, it was as if the man himself stood there in all the actuality of flesh and blood.