Today, we focus the rays of the sun. 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.
Who was Diocles? We don't
really know. All we have is a text he wrote over
2000 years ago. It's not even in his own tongue. It
was written in AD 1462 by a careless scribe who
left only spaces where figures should've gone. But
it's enough to tell us that it was Diocles who
invented the parabolic mirror.
Who was Diocles? Historian G.J. Toomer picks
through this skimpy legacy -- this ancient text,
titled On Burning Mirrors. Most of
what we knew of Diocles came from reference to his
work by a noted 6th-century mathematician. Now we
finally read this copy of his book, penned 1600
years after the fact.
Toomer does his historical detective work. He
decides that Diocles flourished in Greece just after
200 BC. He was a mathematician -- a geometer. Toomer
takes us through the text, recreating the figures. We
read Diocles' opening:
The burning-mirror surface submitted to you is
the surface bounding the figure produced by a
section of a ... cone ... revolved about [its
axis].
That, of course, is the shape of a
paraboloid, and paraboloids touch our modern world in
the technology of solar towers:
A solar tower holds a steam-generating boiler high
above a surrounding field of mirrors shaped into a
gigantic parabola -- one great burning mirror. This
mirror gathers in the energy of the sun and focuses
it on the steam generator. It in turn drives a
turbine. Diocles's mirror is the heart of a power
system that we're still developing.
Diocles began with work Archimedes did a century
before him. Although Diocles makes no such claim,
you and I have heard the legend that Archimedes
used burning mirrors to set the Roman fleet afire
as it invaded Syracuse. The problem is, that that
would've taken a technology beyond even the solar
tower. Archimedes had studied far more primitive
burning mirrors. He didn't yet have Diocles's
efficient parabolic collector.
Before he plunges into the complex geometrical
analysis, Diocles pauses to tell us the practical
value of his theory. He tells how mathematicians
have computed the enormous size of the solar
system. He tells how we might use burning mirrors
in temples for cremations -- how his optics might
improve sundial design. Only then does he write
down the same arithmetic I studied as an
engineering student.
But I still want to know who Diocles was -- this
man bent by the distant lens of history -- this
almost forgotten Greek whose mathematical burning
glass illuminated scholars in Baghdad and
Renaissance Italy. Who was this ancient man who
first designed the solar collectors that will yet
warm our hearths -- in the 3rd millennium AD?
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
Toomer, G.J., Diocles on Burning
Mirrors. New York: Springer Verlag, 1976.
For more on Archimedes's burning mirror death ray,
see Episode 252.
Artist's impression of a large burning mirror
from
Les Entretiens Physiques d'Arste et
d'Eudoxe, 1745
The Engines of Our Ingenuity is
Copyright © 1988-1997 by John H.
Lienhard.
Previous
Episode | Search Episodes |
Index |
Home |
Next
Episode
