Edison’s Puzzle
During
his experiments with the light bulb, Thomas Edison wanted to know why the
filaments broke frequently. Another puzzle was uneven blackening – the filament
always blackened on side. To study this, Edison introduced an extra wire or
foil, into the glass tube, which became a second electrode and connected this
to a galvanometer, which measured the current flowing through this foil. Neither
Edison nor his assistant William Joseph Hammer, understood the blackening, but
they observed a new phenomenon with the introduction of the second electrode.
When the foil was connected to the positive end of a battery, current would
flow from the filament to the foil, but if it was connected to the negative
there was no current. Edison couldn’t explain this phenomenon either, but it
was called the Edison Effect.
A
British scientist John Ambrose Fleming who worked for the Edison Telephone
company in England, visited Edison’s labs in the USA in the 1880s. He too
studied this effect. He later joined Guglielmo Marconi’s telegraph company and
helped Marconi make the first trans-Atlantic radio transmission. Marconi had
launched the era of wireless transmission but a building a practical radio
faced as many obstacles as building Edison’s light bulb.
Heat and Electrons
Meanwhile
science had advanced in leaps and bounds. JJ Thompson had discovered electrons.
Owen Richardson discovered that a heated wire emitted electrons – this phenomenon
was called thermionic emission. This
explained the Edison effect! Remember the incandescent light bulb glows because
electricity causes the filament to become very hot. Light is the visible
byproduct of heat. Thermionic emission is the invisible byproduct of heat. Invisible, but electrically detectable
– the electrons given off by the filament jumped across the vacuum of the light
bulb and flowed through a positive foil – Edison’s second electrode. But if the
foil were connected to a battery’s negative terminal, they foil repelled
electrons which were negatively charged. Edison and Hammer had discovered a
device that would allow current in one direction but not another; but they
could not think of any use for it.
Electronic Era
Two
decades later, in Marconi’s lab in 1904, Fleming recalling this phenomenon
realized that this effect, called rectification was also useful for radio
detection. Fleming called it the oscillation valve – it was later called by
many names, including Fleming valve, thermionic valve, diode, and significantly vacuum
tube.
In 1904,
Lee de Forest, introduced a third porous electrode called the grid, in between
the two electrodes of the diode. Controlling the current of the grid enabled
fine regulation of the current across the vacuum tube. Others later introduced
fourth and fifth electrodes, producing the tetrode and the pentode. This whole
class of devices are now called vacuum tubes. (Meanwhile, the discovery a filament
lasts longer in the bulb filled with inert gases like neon or argon, than when
a vacuum is maintained, meant that light bulbs are no longer vacuum tubes.)
Fleming
and de Forest then had fought over patents and precedence, just as Edison did
over the light bulb and Daimler over his engines and in stark contrast to the
decency and admiration, Wallace and Darwin exhibited towards each other. The
history of technology is littered with such lawsuits, as huge amounts of money
are often involved. In this case, Fleming deserves credit for the vacuum tube
and de Forest for the triode.
Other technologies
have overtaken Fleming’s oscillation valve as a radio detector, but as diodes
they are still widely used as rectifiers, most commonly to convert Alternating
Current to Direct Current.
But vacuum
tubes as a class effectively launched the Age of Electronics. The vacuum tube
most people have used is the Cathode Ray Tube used in televisions and computer
screens, until Liquid Crystal Displays (Flat screens) began to replace them by
the millions. But radio, microwaves, amplifiers and whole host of such devices
are fundamentally vacuum tubes. Most famously, vacuum tubes were the first
practical high speed electronic memory devices used for storing binary
information. The earliest computers, in the 1940s, were built with vacuum
tubes! Hence some historians consider Fleming the Father of the Electronic Age.
Considering how often we use suffixes like “tronic”, it is astounding that
Fleming is not as famous as Edison or Einstein.
The
advent of the silicon diodes and transistors, launched the Age of Semiconductor
electronics. Vacuum tubes are still used in high voltage applications.
Fleming
courted controversy in scientific circles, because he questioned and rejected
Darwin’s Theory of Evolution. Unlike a significant number of European
scientists of the Industrial Era, who were atheists or agnostics, he was a very
devout Christian. Today, we think of scientists as specialists in their field,
so it’s unusual to see a physicist challenge a theory in biology. Scientists
gain reputations for controversy in their own fields.
Inventor, Teacher, Writer
We
learnt of Fleming’s Left Hand rule, from our school physics teacher, holding
out his thumb, forefinger and middle finger, each at a right angle to the
other. These represented the directions of electric force magnetic force and
induced motion, in an electric motor. I often wondered who Fleming was, and why
it was not called Faraday’s Left hand rule. Fleming worked as a lecturer at the
University College, London before his employment with Edison and Marconi. In
his later days, he published several books and delivered several lectures on
Electrical engineering. He formulated the Left Hand and Right Hand rules,
nearly a century after Faraday discovered them. This is now a standard teaching
tactic. Sometimes it takes another scientist to explain simply and lucidly, the
earlier scientist’s discoveries. From Patanjali to Euclid, Parimelazhagar to
Bertrand Russel, commentators have played this important role. Fleming ranks
among them.
Fleming
not merely launched the Electronic Age and advanced the Wireless Era, he also
helped us understand several aspects of the Electric Age. Like Wallace who
wrote widely on several aspects of biology, Fleming lived a long life and wrote
on a vast spectrum of subjects in Electricity. Among the 100 books he wrote are
The Electrical Educator, Fifty Years
of Electricity, The Wonders of Wireless
Electric Telegraphy, The Alternate Current Transformer in Theory and
Practice.
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