In early 1880, Thomas Edison and his team were hard at
work trying to find a light bulb filament that worked well. He had already
settled on a carbonized (burned) bamboo filament, but even this solution was
not perfect. After glowing for a few hours, carbon from the filament would be
deposited on the inside walls of the bulb, turning it black. This would not do.
Edison tried to understand what was happening. His assistant noticed that the
carbon seemed to be coming from the end of the filament that was attached to
the power supply, and seemed to be flying through the vacuum onto the walls of
the bulb. Edison determined that not only was carbon flying through the vacuum,
but that it carried a charge. That is, electricity was flowing not only through
the filament but also through the evacuated bulb. In order to measure this
flow, he made a special bulb with a third electrode, to which he could attach
an instrument to measure the current. He reasoned that if the current would
flow between the two ends of the filament, it would also flow to this third
electrode.
While he was proven to be right about the flow, Edison could not
explain it, and the third electrode did not prevent blackening of the bulb, so
he moved on to other experiments. But he did patent the new device, because he
believed that it might have some commercial applications, such as measuring
electric current. Although he did not realize it, Edison had discovered the
basis of the electron tube (also called a vacuum tube). Many years later,
modified light bulbs would be used not to make light, but to control a flow of
electrons through a vacuum. The electron tube would become the basis of modern
electronics. Years later, when he was elderly, the discovery of what became
known as the “Edison Effect” was remembered, but because Edison had no idea
what it was or how it worked, he is rarely given credit for this contribution
to the development of electronics.