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.
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.
சிலிகான் சிற்பி - வால்டர் பிராட்டன்
Symbiogensis - non Darwinian evolution
Shoulders of Giants - Essays on Scientists