Today, nomograms, analogs, and a forgotten world. The
University of Houston's College of Engineering presents
this series about the machines that make our civilization
run, and the people whose ingenuity created them.

A *digital* computer works a
lot like counting on our fingers. It adds up numbers, one
by one. We can *afford* to do that when even our
home PCs do a billion calculations per second. But the
older *analog* computer had to go at calculation
in subtler ways.

Just as an analog watch is analogous to the face of a
sundial, an analog computer carried out some process that
was analogous to a calculation. The process gave an
approximate (but often quite accurate) output that
*looked like* the result we wanted.

For example, some people created electrical circuits that
obeyed the equation we needed to solve. The output
voltage then behaved like the solution to our problem.
The slide rule was a simpler and
more familiar form of analog computer. Its scales were
logarithmic. Since we can multiply by adding logarithms,
adding distances on two slide rule scales was analogous
to multiplying.

A variation on that idea was a graph called a
*nomogram*. It was set up to solve just one
equation that would've taken a lot of time on a slide
rule, or required scales that no slide rule had.

Here's how a nomogram worked: we had a page with several
lines on it. The lines could be stretched out in many
ways. They might be straight, curved or tilted. We'd
connect points on two lines with a straightedge. Where
the straightedge intersected a third line, we read the
answer. Sometimes we'd have more lines, and we'd have to
get our answer in more than one step.

I have here an old book of nomograms, published in 1911.
We can use them to adjust our pile-driver,
design a masonry
arch, size a water
pipe, or calculate the water flow in a canal. Some of
the diagrams get really ornate. To get the power output of a steam
engine, we navigate a chart with eleven different
lines on it.

Charts like these were once a staple of the engineering
world. Sometimes called *alignment charts* or
*straight-line diagrams,* engineering handbooks
had long sections on how to construct them. As a young
engineer, I collected nomograms made in the form of
specialized cardboard slide rules. Advertisers handed
them out like candy, and we used them to select springs,
gears, or bearings.

Down through the 1950s I cooked up one analog trick after
another for getting numbers. I plotted graphs and aligned
scales. I read books about fancy new forms of analog
computers that inventive people were dreaming up. But the
digital computer, invented in 1939, was quietly catching
up with all this cleverness.

Soon muscle replaced guile in our calculations. We began
to speak of *number crunching.* But the pendulum
swings. Today, we again look for ways to reclaim the
intimacy-with-process we once had. We use neural networks
and fuzzy logic. We develop analog interfaces -- joy
sticks and touch screens. We again seek to make the
computer more nearly analogous to the smooth flow of
action in nature, as well as to the subtle movements of
the human mind.

I'm John Lienhard, at the University of Houston, where
we're interested in the way inventive minds work.

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