"My grandson Bork told me all that," he said. "Yet your name was on the
monument, and we drew you back by its use. Our ancient prophecy declared
that we should find omnipotence carved on stone in a pool of water, as
we found your name. Therefore, by the laws of rational magic, it is
_you_ to whom nothing is impossible. We may have mistaken the direction
of your talent, but nonetheless it is you who must fix the sky. What
form of wonder is a computer?"
Dave shook his head at the old man's monomania. "Just a tool. It's a
little hard to explain, and it couldn't help."
"Humor my curiosity, then. What is a computer, Dave Hanson?"
Nema's hand rested on Hanson's arm pleadingly, and he shrugged. He
groped about for some answer that could be phrased in their language,
letting his mind flicker from the modern electronic gadgets back to the
old-time tide predicter.
"An analogue computer is a machine that ... that sets up conditions
mathematically similar to the conditions in some problem and then lets
all the operations proceed while it draws a graph--a prediction--of how
the real conditions would turn out. If the tides change with the
position of some heavenly body, then we can build cams that have shapes
like the effect of the moon's orbit, and gear them together in the right
order. If there are many factors, we have a cam for each factor, shaped
like the periodic rise and fall of that factor.
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