erald shook himself, as if trying to come back to a normal
and a reasonable world.

"Look!" he said in a hoarse voice. "I saw it, an' I still don't believe
it! Things like this don't happen! I thought you might be lucky. It
ain't that. I thought I might be crazy. It ain't that! What has been
goin' on?"

Brink sat down. His air was one of wry contemplation.

"I told you I had a special kind of luck you couldn't believe. Did your
eyelids twitch any time today?"

Fitzgerald swallowed.

"They did. And I stopped short an' something that should've knocked my
cranium down my windpipe missed me by inches. An' again--But no matter.
Yes."

"Maybe you can believe it, then," said Brink. "Did you ever hear of a
man named Hieronymus?"

"No," said Fitzgerald in a numbed voice. "Who's he?"

"He got a patent once," said Brink, matter-of-factly, "on a machine he
believed detected something he called eloptic radiation. He thought it
was a kind of radiation nobody had noticed before. He was wrong. It
worked by something called psi."

Sergeant Fitzgerald shook his head. It still needed clearing.

"Psi still isn't fully understood," explained Brink, "but it will do a
lot of things. For instance, it can change probability as magnetism can
change temperature. You can establish a psi field in a suitable
material, just as you can establish a magnetic field in steel or alnico.
Now, if you spin a copper disk in a magnetic field, you get eddy
currents. Keep it up, and the disk gets hot. If you're obstinate about
it, you can melt the copper. It isn't the magnet, as such, that does the
melting. It's the energy of the spinning disk that is changed into heat.
The magnetic field simply sets up the conditions for the change of
motion into heat. In the same way ... am I boring you?"

"Confusing me," said Fitzgerald, "maybe. But keep on. Maybe I'll catch a
glimmer presently."

"In the same way," said Brink, "you can try to perform violent actions
in a strong psi field--a field made especially to act on violence. When
you first try it you get something like eddy currents. Warnings. It can
be arranged that such psi eddy currents make your eyelids twitch. Keep
it up, and probability changes to shift the most-likely consequences of
the violence. This is like a spinning copper disk getting hot. Then, if
you're obstinate about it, you get the equivalent of the copper disk
melting. Probability gets so drastically changed that the violent thing
you