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 l