Today, water's own level. The University of Houston's College of Engineering presents this series about the machines
that make our civilization run and about the people whose ingenuity created them.
I Googled the phrase "water seeks its own level" and got a third of a million hits.
Few said anything about hydrostatics. Most saw it as a metaphor for how things equalize in society.
The principle actually says that the water levels in two basins, connected by a pipe, must be the same.
That had to've been known long before Aristotle; but Aristotle articulated it and wrote it down.
Now it's a rainy season in flat Houston, Texas. The levels in every pool or bayou here are quite close to
one another. And it's important that water should find its lowest level as soon as possible. Our streets
become streams, and we realize these streams lie only a few feet above the nearby swollen bayou. But we're
protected by large storm sewers and a network of detention basins. We rely on a passive system
that needs no pumping. It functions entirely on water's eternal quest for its own level.
Yet, while water's level-seeking might seem obvious, it can fool us. Think about the iffy way we perceive
"level" on Earth's surface. If we've ever been to a "Mystery House" or "Vortex House" we know what that means.
Those misaligned buildings make us think that gravity has gone crazy.
So it often is when we drive a slightly sloping road and think we're going horizontally. Rainfall runoff
often flows in ways we don't quite expect. It's easy to get it wrong without using a surveyor's level.
And, even with instruments, people have, now and then, gotten it very wrong indeed.
Napoleon once considered building a Suez Canal. But he abandoned the idea when his surveyors mistakenly
reported that the Red Sea was 33 feet higher than the Mediterranean. They told him that a canal would need
an elaborate system of locks. That of course was absurd. Both seas are connected and have to seek the same
level. (By the way, the Panama Canal has locks only to take ships up to Lake Gatun -- then back down to
the ocean again.)
Then there's hydrostatic perpetual motion -- one of so many schemes people have dreamt up for making gravity
give us free power. The idea is to create a wide vessel that narrows into a slender pipe. That pipe curves
around and points upward. Since the water in the wide vessel is heavier than the tendril in the pipe, it's
supposed to drive water far above the surface in the vessel.
Alas water pressure depends only on the depth, not at all on the breadth, of a pool. So this is one more
doomed dream. Water in the skinny pipe goes to the water level and stops there. So too with rain falling
on Houston: Where will it stop? Well, at exactly the level of the distant detention basin that saves us
For some, the water-level principle is as depressing as rain itself. The principle is so -- flat! But here
we one need only find that nearby muddy detention basin, teeming with the rebirth of birds, grass and flowers.
To stand and admire a water level that lies just a bit lower than all the safe surrounding homes.
I'm John Lienhard at the University of Houston, where we’re interested in the way inventive minds work.
Here is a useful online primer on the subject of hydrostatics.
See also, the Harris County Flood Control District's page on storm water detention.
And, this page describes several kinds of hydrostatic perpetual motion machines.
Photos are by John Lienhard. They show the Meyerland detention basin above and the Willow Waterhole basin below. The hydrostatic
perpetual motion machine was adapted from a Wikimedia Commons sketch.
This episode was first aired on March 19, 2012
The Engines of Our Ingenuity is
Copyright © 1988-2012 by John H. Lienhard.