|
February 1947 Popular Science
 [Table of Contents]
Wax nostalgic about and learn from the history of early
electronics. See articles from
Popular
Science, published 1872-2021. All copyrights hereby acknowledged.
|
Imagine how much it must
have tortured Thomas Edison to find out he had been the first to discover
thermionic electron flow, the basis for all future vacuum tube technology, and
did not recognize it at the time. As reported in this 1947 issue of Popular
Science magazine, Mr. Edison made his finding in 1883 while investigating
designs for electric light bulbs. Ambrose Fleming recognized the significance of
the phenomenon in 1904 when he built the world's first diode tube. Three years
later, Dr. Lee de Forest
inserted a modulating grid between the cathode and anode and, voila, the
amplifier tube was born (the audion). Edison died in 1931 with the knowledge
that his fame and fortune resulting from his electric light bulb, talking
machine (phonograph), moving pictures, stock ticker, multiplex telegraph,
storage battery, fluorescent lighting, Portland cement, and multitudinous other
inventions could all have been trumped by the missed discovery of the diode and
triode. You might be tempted to think he probably was content with his credited
accomplishment, but that's not the way genius overachievers work.
Edison's Magnificent Fumble
 By Robert D. Potter
Was the greatest accomplishment of America's leading inventor a find he overlooked?
America's No.1 inventor just missed one of the greatest inventions of all time.
But he discovered the clue that enabled others to perfect it.
Most of those who currently celebrate the 100th anniversary of the birth of Thomas
Alva Edison at Milan, Ohio, on February 11, 1847, remember him, for his electric
light, talking machine, and moving pictures.
Many recall, too, his stock ticker, multiplex telegraph, storage battery,
fluorescent lighting, and Portland cement.
Perhaps few, in contrast, ever heard of the Edison effect, to which we owe the
vacuum tube and the marvels built around it - radio, television, radar, electron
microscopes, atom smashers, and unknown wonders still to come.
Electrons boiling from the carbon filament of Edison's lamp gave the clue to
the vacuum tube.
To Edison, the phenomenon that bears his name was no boon, but an unmitigated
nuisance. Back in 1883, the Wizard of Menlo Park was fretting over his electric
lamp. It burned brightly for a time, then sputtered and went out. Its bulb blackened.
Something was carrying the very substance of the filament across empty space to
the glass.
  Fleming's diode tube of 1904 harnessed the Edison effect to change alternating
current into direct current. Employed as a detector of ether waves, it opened the
way to modern radio.
De Forest inserted a grid between filament and plate of his audion tube
and the radio amplifier was born. Feeble signals applied to the grid start and stop
the flow of a stronger current passing through the tube.
Descendants of the two pioneer vacuum tubes have transformed our lives and language.
"Wireless" of Marconi's time evolved into radio. It is now frequently given the more
precise name of AM or amplitude modulation.
Static-free FM, or frequency modulation, now challenges the supremacy of the
older system of broadcasting. And, some day, both AM and FM may be outmoded. But
the basic principle they apply - Edison effect - lives on.
Edison inserted a metal plate in a lamp bulb, and attached a current meter. Its
needle swung. Jotting down his observation, the busy inventor hastened away to other
experiments of more obvious practical importance. Had he only known it, he had in
his grasp the key to the whole vast science of electronics. For the meter proved
that the filament was "boiling off" charged particles - electrons, we call them
now. And they would flow in only one direction, from the filament to the plate.
More than two decades later, a British physicist, J. Ambrose Fleming, awoke to
the significance of this Edison effect. It provided, he realized, a one-way valve
for converting alternating into direct current. Embodied in his diode or two-element
vacuum tube of 1904, it supplied the practical means of detecting wireless waves
that the world had been waiting for. In 1907, Dr. Lee de Forest added a third element
- a grid to control the current flow between filament and plate - and obtained,
in his triode or audion, an amplifier that augmented the volume of faint reception
until it could be clearly heard. Listeners took off their ear-phones - and wireless,
given new ears and voice, became modern radio.
Just as truly as Fleming's diode and de Forest's triode became the main branches
of the mighty family tree of electronics, so the Edison effect gave root to it.
In a very real sense, the major types of vacuum tubes shown with their applications
on these pages are Edison's unwitting brain children - and his greatest claim to
fame may well be the discovery of a principle that will live on, even after all
the inventions he made himself have been superseded by later developments and have
passed from memory.
Striking a metal target, cathode rays generate X-rays used to make radiographs
of human bones, treat cancer. and examine steel for flaws.
First applied in diathermy, high-frequency radio waves of pliotron tube now heat-treat
steel for gears and tools and bond the layers of plywood.
Radar, which spots war targets and aids peacetime navigation uses klystron tube
to bounce signals against planes, ships, mountains - and even the moon.
Television cameras and receivers attained quality definition when weightless
beam of cathode-ray tube ended speed limits on scanning.
Photoelectric tubes count people, cars and factory products, open doors, make
sound movies, and transmit copies of messages and pictures.
Electronic precipitation abates smoke by attracting particles to plates connected
with kenetron tubes, which provide a high-voltage source.
The thyratron, a versatile tube, can handle large current output for welding,
and serve as a "slave" to toke orders from phototubes.
Ignitron tubes have two major functions - to turn alternating into direct current,
and as a timing and switching device for arc welding,
Allowing the men of science to probe deeper than they ever did before, the electron
micro-scope is capable of magnification up to 180,000 diameters.
Posted November 11, 2023
|
