upon the demonstrator who completely ignored this sign of disbelief.

"Inside the control box is the battery," the young man said, snapping it open and pointing to an ordinary flashlight battery. "The current goes through the Power Switch and Power Light to the Wave Generator ..."

"What you mean to say," Biff broke in, "is that the juice from this fifteen cent battery goes through this cheap rheostat to those meaningless coils in the model and absolutely nothing happens. Now tell me what really flies the thing. If I'm going to drop eighteen bucks for six-bits worth of tin, I want to know what I'm getting."

The demonstrator flushed. "I'm sorry, sir," he stammered. "I wasn't trying to hide anything. Like any magic trick this one can't be really demonstrated until it has been purchased." He leaned forward and whispered confidentially. "I'll tell you what I'll do though. This thing is way overpriced and hasn't been moving at all. The manager said I could let them go at three dollars if I could find any takers. If you want to buy it for that price...."

"Sold, my boy!" the colonel said, slamming three bills down on the table. "I'll give that much for it no matter how it works. The boys in the shop will get a kick out of it," he tapped the winged rocket on his chest. "Now really—what holds it up?"

The demonstrator looked around carefully, then pointed. "Strings!" he said. "Or rather a black thread. It runs from the top of the model, through a tiny loop in the ceiling, and back down to my hand—tied to this ring on my finger. When I back up—the model rises. It's as simple as that."

"All good illusions are simple," the colonel grunted, tracing the black thread with his eye. "As long as there is plenty of flimflam to distract the viewer."

"If you don't have a black table, a black cloth will do," the young man said. "And the arch of a doorway is a good site, just see that the room in back is dark."

"Wrap it up, my boy, I wasn't born yesterday. I'm an old hand at this kind of thing."

Biff Hawton sprang it at the next Thursday-night poker party. The gang were all missile men and they cheered and jeered as he hammed up the introduction.

"Let me copy the diagram, Biff, I could use some of those magnetic waves in the new bird!"

"Those flashlight batteries are cheaper than lox, this is the thing of the future!"

Only Teddy Kaner caught wise as the flight began. He was an amateur magician and spotted the gimmick at once. He kept silent with professional courtesy, and smiled ironically as the rest of the bunch grew silent one by one. The colonel was a good showman and he had set the scene well. He almost had them believing in the Space Wave Tapper before he was through. When the model had landed and he had switched it off he couldn't stop them from crowding around the table.

"A thread!" one of the engineers shouted, almost with relief, and they all laughed along with him.

"Too bad," the head project physicist said, "I was hoping that a little Space Wave Tapping could help us out. Let me try a flight with it."

"Teddy Kaner first," Biff announced. "He spotted it while you were all watching the flashing lights, only he didn't say anything."

Kaner slipped the ring with the black thread over his finger and started to step back.

"You have to turn the switch on first," Biff said.

"I know," Kaner smiled. "But that's part of illusion—the spiel and the misdirection. I'm going to try this cold first, so I can get it moving up and down smoothly, then go through it with the whole works."

ILLUSTRATED BY BREY

He moved his hand back smoothly, in a professional manner that drew no attention to it. The model lifted from the table—then crashed back down.

"The thread broke," Kaner said.

"You jerked it, instead of