Today, we find a rejected invention that changed
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 "Edison effect" was the
name given to a phenomenon that Edison observed in
1875 and refined later, in 1883, while he was
trying to improve his new incandescent lamp. The
effect was that, 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 patented it
anyway. Edison patented everything in sight. Today
we call the effect by the more descriptive term,
Now the Edison effect has an interesting feature.
The electrons can flow only one way -- from the hot
element to the cool plate, but never the other way
-- just like the water flow through a check valve.
Today we call devices that let electricity flow
only one way, diodes.
In 1904, the Edison effect was finally put to use,
but not in a light bulb. Radio was in its infancy,
and the British physicist John Fleming was working
for the British "Wireless Telegraphy" Company. He
faced the problem of converting a weak alternating
current into a direct current that could actuate a
meter or a telephone receiver. Fortunately, Fleming
had previously consulted for the Edison & Swan
Electric Light Company of London. The connection
suddenly clicked in his mind, and 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. Fleming, in other words, invented the first
vacuum tube. Of course, most vacuum tubes have been
replaced with solid-state transistors today; but they
haven't vanished entirely. They still survive, in
modified forms, in things like television picture
tubes and X-ray sources.
Fleming's discovery reveals an aspect of the
creative process that comes at us again and again.
The creative inventor takes ideas out of their
original contexts and uses them in new contexts. He
turns bread-mold into penicillin, coal into
electricity -- or, I suppose, lead into gold --
because he isn't constrained to keep each thought
in its own container.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds