Engines of Our Ingenuity

No. 1770:

by John H. Lienhard

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 opposed.

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 out there.

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.


(Theme music)

For an online Army marching and drill manual, see: http://www.military-net.com/education/mpddrill.html

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 Good Soldier Svejk

The Good Soldier Svejk on the march (See Episode 1339.)
