Published On: Fri, Feb 13th, 2015

Thomas Edison discovers the ‘Edison Effect’ which leads to ‘horseshoe filament’

Thomas Edison’s legacy as the “Man who invented the ligh bulb” took a major step forward on this day in 1880 as he first observed the “Edison Effect.”

In 1960 an article appeared in the American Journal of Physics (Vol 28, No 9, December, 1960, pages 763-773) by J. B. Johnson that told of the “Contribution of Thomas A. Edison to Thermionics.”

The article puts Edison’s work in perspective with the work of others, both before and after his work. , as well as his observations made during the development of the Edison lamp.

Wiki makes the definition: The classical example of thermionic emission is the emission of electrons from a hot cathode into a vacuum (also known as thermal electron emission or the Edison effect) in a vacuum tube.

Johnson wrote that “…Edison was busy in his laboratory at Menlo Park developing his carbon filament incandescent lamp. The lamp was not on the market yet, but it looked very promising. The filament at that time was cut horseshoe shaped out of a certain kind of calling card, then carbonized and mounted on the lamp stem. This was sealed into a glass bulb that was then pumped with a Sprengel dropping mercury pump….”

“On February 13, 1880, Edison entered in his notebook the first of a long series of experiments on prevention of carrying. The drawing shows a lamp with the “horseshoe” filament, and an extra electrode inserted, a piece of platinum foil. The test was made by Charles Batchelor, one of Edison’s engineers….”

This leads to amazing developments years later: the diode, a two-element vacuum tube and the ability to detect radio waves – just to name a couple.

Johnston detailed a long history before noting that “…The discovery of large currents flowing from a hot filament was not something that was recorded in a notebook and forgotten. Edison told people about it, he applied for a patent describing and making use of it, he caused it to be reported in the scientific literature, and it aroused a lively interest among eminent men of the day. The explanation of the phenomenon had to wait a couple of decades for the revolutionary ideas of Thompson, Drude, and Richardson. The truth then turned out to be that the carriers of negative charge were not carbon atoms in Edison’s experiments or other gas molecules in the Crookes effect, but electrons in both. Edison’s contribution was not to explain the phenomenon, but to create and keep alive a keen interest in the mysterious side effect that showed up in the blackening of lamps, the Edison effect.”

A little more history and understanding of the invention process reveals even more of Edison’s genius.

photo Ulfbastel

photo Ulfbastel

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