vel scientific brains. Mathematicians
zestfully contrive problems to stump each other. Specialists in the
higher branches of electronics sometimes present each other with
diagrammed circuits which pretend to achieve the impossible. The problem
is to find the hidden flaw.

Graves deftly outlined his circuit and began to fill in the details.
Ostensibly, it was a circuit which consumed energy and produced
nothing--not even heat. In a sense it was the exact opposite of a
perpetual-motion scheme, which pretends to get energy from nowhere. This
circuit pretended to radiate energy to nowhere, and yet to get rid of
it.

* * * * *

Presently Lecky could be heard expostulating gently:

"But of course we are willing to give you the circuit by which we
communicate with the year 3020! Naturally! But it seems strange that you
suspect us! After all, if you do not tell us how to meet the danger your
broadcasts have told of, you will never be born!"

Sergeant Bellews mopped his face and moved into the screen's field of
vision.

"Doc," he said, laying a hand on Lecky's arm. "Doc Graves is sketchin'
what they want right now. You want to come show it, Doc?"

Graves took Lecky's place. He spread out the diagram, finishing it as he
talked. His nervous, faint smile appeared as the mannerism of
embarrassment it was.

"There can be no radiation from a coil shaped like this," he said
embarrassedly, "because of the Werner Principle.... Yet on examination
... input to the transistor series involves ... energy must flow ...
and when this coil...."

His voice flowed on. He explained a puzzle, presenting it diffidently as
he had presented it to other men in his own field. Then he had been
playing--for fun. Now he played for perhaps the highest stakes that
could be imagined.

He completed his diagram and, smiling nervously, held it up to the
communicator-screen. It was instantly transmitted, of course. To
nowhere. Which was most appropriate, because it pretended to be the
diagram of a circuit sending radiation to the same place.

* * * * *

The face on the screen twitched, now. The hand with the tiny earphone
was always at the ear of the man on the screen, so that he plainly did
not speak one word without high authority.

"_We will--examine this_," he said. His voice was a full two tones
higher than it had been. "_If you have been--truthful we will give you
the information