Today, let's meet Jean-Charles Borda. 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.
I find it wonderfully odd -- how names outlive the people they
once belonged to. I talk with younger engineers who studied in UCLA's
Boelter Hall.
They look at me oddly when I mention having talked with Boelter,
for one does not converse with a name on a building. We in technical fields attach
so many names to theorems, laws, and devices without any mental picture of the people.
I once worked on metering orifices, and one such meter was the Borda Mouthpiece. It's
a short tube inserted into the wall of a tank. Water inside does a 180-degree turn into
the tube, forms a perfectly clean jet, and leaves without touching the tube walls.
Elementary theory, says the jet should have exactly half the area of the tube.
That would allow the device to meter the flow very accurately; but there's a catch:
Everyone who's ever tested a Borda mouthpiece has measured a flow that's high by several
percent. Why? A colleague and I finally solved that riddle -- both experimentally and
theoretically -- and we showed how to correct the measurement.
Yet we did all that with no clue -- no thought -- about the person of Jean-Charles Borda.
And that's a shame, because Borda was a remarkable figure. He was born of French
aristocrats in 1733. After his education, he worked the rest of his life as a military
engineer and as a naval officer. All the while, he did wonderfully creative scientific
and engineering work.
At the age of 31, he was made a member of the French Academy for his work on the physics
of projectiles. His studies of energy conservation laid ground for the subject of
thermodynamics. He invented a new surveying instrument called a
reflecting circle.
He worked in the Caribbean testing new longitude chronometers.
In 1770 Borda proposed a method of voting for multiple candidates. Using the so-called
Borda count, voters rank candidates from a low of one to a high equal to the number
of candidates. The points are summed to name the winner. Alas, mathematical economist Kenneth Arrow
later showed that, not only does a simple majority fail to produce the most desired candidate
-- neither does Borda's method.
But that was still the idea of a rationalist looking for better self governance. He fought
with the French in the American Revolution -- eventually put in charge of six vessels. His
war ended in 1782, when the British captured him. After his release, he turned his attention
to hydraulics -- and to my own Borda tubes.
Late in life, he was part of yet another rationalist cause: He served on the blue-ribbon
committee that defined the meter as one ten-millionth of the distance from the pole to the
equator.
So, years ago, I watched the frozen motion of perfect jets leaving inverted tubes and did not
imagine the swirling creative energy behind it. I didn't dream, as I ought to have dreamt,
that Borda was so much more than a name randomly attached to a device.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
C. S. Gillmor, Borda, Jean-Charles. Dictionary of Scientific Biography,
C. C. Gillispie, ed., Vol. II (New York: Charles Scribner's Sons, 1970): pp. 299-300.
W-g Dong and J. H. Lienhard, Contraction Coefficients for Borda Mouth-pieces.
Journal of Fluids Engineering, Vol. 108, No. 3, Sept. 1986, pp. 377-379. To read
this source on-line, Click Here.
See also: http://en.wikipedia.org/wiki/Jean-Charles_de_Borda
and http://www-groups.mcs.st-and.ac.uk/history/Biographies/Borda.html
For more on Arrows impossibility theorem see Episode 1921, and:
http://en.wikipedia.org/wiki/Arrow's_impossibility_theorem
Three Borda tubes (or mouthpieces): Borda's theory predicts the flow to be (A/2)�(2gh)1/2
(where A is the cross-sectional area of the tube, g is the gravitational acceleration,
and h the liquid head in the supply tank.) But the length of the tube must be far
longer than the diameter for that to be true. The shortest tube shown here gives
a flow rate that is high by eight percent. It is high by about one percent for the
longest tube. (JHL's scanned image)
Borda tube experiment (Dong and Lienhard.)
The Engines of Our Ingenuity is
Copyright © 1988-2006 by John H.
Lienhard.
