Today, let's not pull together. 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.
When I did my two years in
the Army, I counted seconds until I could get out.
Yet, two unlikely activities created a sense of
well-being: While KP was a grueling fifteen-hour
stretch of kitchen labor, it nevertheless served
the essential task of feeding people. Nothing I
want to repeat, but it felt good to've done it.
The other was close-order drill -- forty people
moving as one. What a wonderful thing to be totally
subsumed into the group, an individual whose only
identity is that of the whole! That kind of
acceptance is something we all crave.
Yet it has its problems. The U.S. Army marches at
120 two-and-a-half-foot steps per minute. We moved
at 3.41 miles per hour, but our legs were not all
the same length. When an army really wants to
get somewhere, it uses the command
route step, which means, "walk as you
please, but keep up with the group."
In fact, Army regulations require that
route step be ordered for any column marching
across a bridge. Large groups, marching in step,
can set up sympathetic vibrations in a structure.
If conditions are right, those vibrations can bring
down a bridge.
So there's mischief to being in step. And that
comes back to us in another metaphor -- the
metaphor of positive
feedback. Any engineer who knows about
control systems will tell you that positive
feedback is extremely dangerous. It means an action
to augment behavior that should, instead, be
A thermostat using positive feedback will turn the
furnace on when the room temperature rises above 72
degrees. To counter the rising temperature we need
negative feedback, or opposition.
Look at this another way. Ask yourself where a wise
person would choose to build a house of cards: on a
solid marble counter or on a shaky card table. The
better place would actually be on the shaky card
table. The house of cards will be much harder to
build. But we succeed when we build a far more
robust card house.
Now, these are troubled times. Yet have any times
in our lives been untroubled? Never mind
our private politics, let's take a page from our
engineering handbook (or our army manual). Tory and
Whig alike, let's march out of step, for unanimity
threatens the structure. Baptist and Buddhist,
let's all apply negative feedback: question our
friends and listen to our enemies -- build our
houses of cards right in front of the rowdy world
We once had no way of reaching temperatures below
the boiling point of liquid helium. Then we found
that molecules of certain salts, placed in a
magnetic field, fall into alignment and heat up.
Cool such a magnetized salt to the temperature of
liquid helium, release the magnetic field, and the
molecules become disordered once more. The
temperature drops far below that of the helium.
So let us take pleasure in our disorder. Let us
lower the temperature and protect the bridge. Let
us not all pull together.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
For an online Army marching and drill manual, see:
For the refrigeration process called adiabatic
demagnetization, see: P. S. Epstein, A Textbook
of Thermodynamics, New York: John Wiley and
Sons, Inc., 1937, pp. 352-354.
For more on this general theme, see: http://www.uh.edu/engines/hisd.htm
The Engines of Our Ingenuity is
Copyright © 1988-2003 by John H.