Today, an analogy changes our world. 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.
The name Edison
Effect was given to a phenomenon Edison
observed in 1875, although it'd been reported two
years earlier in England. Edison refined the idea
in 1883, while he was trying to improve his new
incandescent lamp. The effect is this: in a vacuum,
electrons flow from a heated element -- like an
incandescent lamp filament -- to a cooler metal
plate.
Edison saw no special value in the effect, but he
applied for a patent anyway. Edison patented
anything that might ever be of value. Today we call
the effect by the more descriptive term
thermionic emission. In any case, the magic
of the effect is that electrons can flow only from
the hot element to the cool plate, but not the
other way. Put a hot and a cold plate in a vacuum
and you have an electrical check valve just like
check valves in water systems. Today we call a
device that lets electricity flow only one way a
diode. It was 1904 before anyone put the effect to
use. Then the application had nothing to do with
light bulbs.
Radio was in its infancy, and the English scientist
John Ambrose Fleming was working for the British
"Wireless Telegraphy" Company. Fleming faced the
problem of converting a weak alternating current
into a direct current that could actuate a meter or
a telephone receiver. Luckily, he'd previously
consulted for the Edison & Swan Electric Light
Company of London. The connection suddenly clicked
in his mind. He later wrote,
To my delight I ... found that we had, in this
peculiar kind of electric lamp, a solution ...
Fleming realized that an Edison effect lamp would
convert alternating current to a direct current
because it let the electricity flow only one way.
So he created the first vacuum tube. By now,
vacuum tubes have largely been replaced with
solid-state transistors; but they haven't vanished
entirely. They still survive, in modified forms --
in things like television picture tubes and X-ray
sources.
Fleming lived to the age of 95. He died just as
WW-II was ending, and he remained an old-school
conservative. Born before Darwin, he was
anti-evolution to the end. Yet even his objection
to Darwinism had its own creative turn. "The use of
the word evolution to describe an automatic process
is entirely unjustified," he wrote, turning the
issue from science to semantics.
In an odd way, semantics marked Fleming's invention
as well. He always used the term valve for
his vacuum tube. In that he reminds us that true
inventors take ideas out of context and fit them
into new contexts. Fleming stirred so much together
to give us the vacuum tube -- light bulbs, radio,
and water supply systems.
But that's how invention works. Inventors turn
bread-mold into penicillin, coal into electricity,
and, at least figuratively, lead into gold, by
refusing to keep any thought in its own container.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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