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These first caught Edison’s attention, but he had never time for further investigations; otherwise, as David Bodanis suggests, Edison may have discovered electrons before J.J. Thomson.

Edison could be said to be the grandfather of electronics. During his investigation of aging effects in his incandescent lamps, he added a small metal plate adjacent to the filament (but not touching it), and brought a connection to it out the side of the bulb.

[Edison was the ideal guy to do this, because in the 1880's nobody was better at building evacuated glass bulbs with things like filaments and plates and bringing their connections out through gas-tight seals in the glass.]

Anyway, he noticed that you could get an electrical current to flow from the plate to the filament through the vacuum, provided you connected the + end of a battery to the plate and the - end to one of the filament leads. I don't think that anybody else had thought, at that stage, that such a thing could happen.

Oh, and one other thing about this phenomenon (that came to be called the "Edison Effect"): current would not flow in the other direction. You could hook up the battery - to the plate and its + to the filament, and nothing would happen.

Bear in mind that Edison's electrical system was exclusively DC--direct current. He had no use for a device that admitted current flow in one direction but not the other, because any element in his system would always be passing current in one direction only.

So, after patenting a device that made trivial use of his gadget, he set it aside. A few physicists here and there got copies of the gadget and investigated it, and then they too set it aside.

Meanwhile, radio was invented by the likes of Tesla, Marconi, and Preece.

One of the early problems with radio transmission was that the first receivers were incredibly insensitive. An example was the "coherer" of Edouard Branley, an insulating tube filled with fine iron filings, which could be made to conduct when furnished with a pulse of radio frequency energy from the aerial. As a result of the deafness of the available receivers, transmitters in the first decade of the 20th centry were being built to gargantuan proportions in order to get enough power into the distant receivers for them to operate. In effect, the receivers were directly transmitter-powered.

So the search was on for a better detector, the heart of the receiver that could turn radio waves from the aerial into currents that could operate things such as telegraph sounders.

Around 1904, John Ambrose Fleming, an English physicist, pulled a dusty Edison apparatus out of a drawer. He reasoned that a device that could pass current in only one direction--that is, it could rectify--might the the ticket to a better detector. In a short time, he hooked it up in a receiver and got an astounding improvement in sensitivity.

Although this was not the only innovation in early radio receivers (the Galena crystal and cat's whisker were another), it set radio technology on a rapid growth curve.

About four years later, a young Stanford PhD on the west coast by the name of Lee DeForest reprised Edison's experiments of two decades previous, in order to better understand the behaviour of what was now being called the "Fleming Valve." This time, he inserted a third element between filament and plate which he called a "grid." He discovered that varying potentials on the grid controlled the flow of current from the plate to the filament, and that he could control a given amount of current with a small amount of voltage. Thus, his gizmo was the first electronic device to exhibit gain. And thus not just radio, but electronics itself was finally born.

Had Edison done his work just ten years later, and had he been developing AC systems, he might have been the father and not just the grandfather of electronics. As it was, DeForest was the father and Fleming, you might say, was the midwife.

Postscript: In 1897, amidst the early development of radio, English physicist J. J. Thompson used an early version of the cathode ray tube to discern the nature of the effect that gave the tube its name. In doing so, came up with convincing evidence that the current through the vacuum was being carried by tiny, tiny particles which he called "electrons." Further experiment revealed the charge and mass of the electron, and established that it was a constituent of the atom--the first subatomic particle to be discovered. It was also shortly established that the electron was also the carrier of electric current through ordinary conductors as well.

One final discovery. According a convention in electrical research that was long established even in 1897, Thompson found that the charge on the electron was negative. Therefore, in the various electron devices here described, the "conventional current" was flowing in the device from plate to filament, but in actuality the negative electrons were flowing from filament to plate. A fact that confuses beginning EE students to this very day. ≤}B^)