ed with
an overlap of red and black and then you could see each high and low
pressure area work its way across the country and out to sea. But
there was a difference. After a couple hours, on their time scale,
Pheola's map differed from the actual, and the difference grew greater
for a while, and then narrowed. Suddenly the red and black lines were
identical.

The cycle repeated several times in the thirty-day period.

"What you see," said Norty, "is that she is right for a few hours and
then wanders off, sometimes for several days, but wanders back and
gets right again. The timing of when she is right is rather
random--there's no regular periodicity to it, and as a result, we
can't see how to predict when she is going to be right and when she is
not."

"I have a thought for you," I said, when Norty had shut off the
projection. "It's sort of like two sine waves that intersect now and
then. One of them has bigger amplitude than the other, or their
periodicity is different. Can't you feed this dope to your computers
and find out what kinds of curves would represent the coincidences?"

He gave me a suffering look. "Don't you suppose I tried that? I get
indeterminate solutions--the machine can't find any curves that answer
the data."

Pheola got her own answers out of that. "Then you don't know whether I
am right about Maragon or not."

"We know that you may not be right, that's something," I reminded her.
"Come on up to the apartment. This calls for some thinking."

Pheola protested that. "Please, Lefty," she said, "this has got me all
shaken up. I'd like to be alone for a while. Will you come and get me
for dinner?"

"Sure," I said.

* * * * *

Pheola was in better spirits by dinner time, and didn't exactly pick
at her food. At any rate, she was ready to talk when we finally got
back to my apartment.

"Did you understand what I said to Norty about the sine waves,
Pheola?" I asked her.

She shook her head. Her education had not proceeded to calculus, and
her trig was too far behind her for quick recollection of what sine
waves were.

I drew some sketches of overlapping sine waves for her to explain what
I thought was going on. "You are making predictions on this one path,
and actual events are on another path, do you see?" I said. "When the
two paths cross, the events that you predict and actual events are the
same, and at those times you're right."

"I know," she said. "