Way back in 1802, Humphrey Davy, one of the most brilliant chemists of all time, became interested in the novel phenomenon of electricity.聽By this time he had already published a treatise on the pain killing properties of laughing gas and had suggested it's use in surgical operations.聽As a result of his chemical prowess he was invited to further his career at the Royal Institution in London, which had been established with the object of "combining useful knowledge with the amusement and instruction of the higher ranks."
Davy had closely followed the work of Alessandro Volta in Italy who had just discovered that grasping wires attached to silver and copper plates separated by moist cardboard caused a shock akin to grabbing an electric eel.聽He had of course created a primitive battery.聽Davy recognized this effect as an excellent candidate for combining useful knowledge with amusement.
In the basement of the Royal Institution he installed a battery made out of 2000 of Volta's "cells" and noted that a wire connecting the ends would glow red.聽Here was a method to produce both heat and light!聽Could this spell the end of the inefficient and often dangerous gaslights?
Unfortunately, the glow did not last long because the wire melted.聽No material that Davy had available could withstand the intense heat produced.聽But Davy did note that sometimes as the wire melted through, a spark jumped between the two disconnected ends.聽Intrigued by this phenomenon, he soon discovered that if the wire were interrupted by two pieces of charcoal which were separated by just the right distance, a continuous spark, or electric arc, was generated.聽The light produced by the sparks and the glowing charcoal was brilliant!
The practical use of arc lamps, however, had to wait for another one of Davy's discoveries, namely Michael Faraday.聽As a youngster, Faraday had worked for a bookbinder.聽One day, a customer brought in a volume of the Encylopaedia Britannica for repair and, as luck would have it, the book fell open to a page featuring an entry on Electricity.聽Faraday was absolutely captivated and wanted to learn more.聽He began to attend Davy's famous public lectures at the Royal Institution and was soon hired by the great man as a laboratory assistant.
Faraday went on to a brilliant career, unravelling many of the secrets of electricity and magnetism.聽Perhaps his greatest contribution was the discovery that moving a coiled wire in a magnetic field caused an electric current to flow through the wire.聽The electrical generator, or dynamo, was born!
Now arc lights could proceed full steam ahead.聽Generators powered by steam delivered the needed electricity and soon London streets basked in an almost daylight glow.聽But even though the public was dazzled by the brilliant light, many scientists had long realized that arc lights were impractical; they needed constant servicing and were much too bright for home use.
Davy's observation of the glowing wire had certainly not been forgotten.聽Could a substance be found that would not melt when a strong current flowed through it?聽As early as 1841, the Englishman Frederick DeMoleyns patented an electric bulb which featured powdered charcoal between platinum wires.聽This produced light for a few minutes but then the charcoal burned.聽His countryman Joseph Swan improved the performance in 1848 by making filaments from paper strips coated with charcoal which he baked to a high temperature in a pottery kiln.
And then Swan had a bright idea.聽If air were pumped out of the bulb, there would be no oxygen present and the charcoal could not burn!聽Since vacuum pumps had recently been invented, he was able to put his idea to a test.聽In 1878 he demonstrated an evacuated bulb with a glowing carbon filament.
This is where Edison enters the picture.聽Hundreds of inventions including the stock ticker and the phonograph had already made him rich and famous.聽He now began to focus his energies and massive resources on taking a scientific curiosity, namely the light bulb, and turning it into a practical commodity.
Edison accomplished this virtually by brute force.聽His "insomnia squad" of workers systematically tried over 1600 different filaments hoping to find one that could stand up to the electric current without being destroyed.聽These ranged from beard hair to carbonized sewing thread.聽 Finally, in 1879, just 14 months after the search began,聽Edison stripped a thin piece of bamboo from a fan in his office and heated it in an oxygen free environment until it carbonized.聽The bamboo filament glowed in an evacuated bulb for 40 hours!
Edison's genius, however, lay not only in producing a practical bulb but in immediately envisioning and designing a complete electrical distribution network, from the power plant and transmission wires to home switches and sockets.聽On New Year's Eve, 1880, he dazzled more than 3000 onlookers when he lit up his Menlo Park "invention factory" in New Jersey with forty bulbs.
Within two years, Edison had built the Pearl Street Generating Plant in Manhattan and was supplying electricity to 85 houses, shops and offices.聽The American had carefully patented his progressive discoveries, something Swan had not done.聽 Edison now had the temerity to sue Swan for patent infringement, in spite of the fact that Swan had built his first light bulb when Edison was only one year old!聽 Eventually the two settled their differences and collaborated in the commercial production of "Ediswan" bulbs.聽
Of course the Ediswan bulb has been improved upon.聽Filaments made of tungsten, the highest melting of all metals, were introduced in 1911.聽These bulbs burned for hundreds of hours before the tungsten evaporated, often producing the characteristic black deposit on the inside surface of a burned-out bulb.聽
Filling the bulb with a mixture of argon and nitrogen slowed this evaporation and allowed for the production of bulbs that could function at higher temperatures and produce more light.聽Then if a halogen, such as iodine, were included in the bulb, it reacted with the evaporating tungsten atoms and redeposited these on the filament.聽These halogen lamps could therefore operate at even higher temperatures and produce even brighter light.聽But bulbs had to be made of more expensive quartz because ordinary glass would melt at these temperatures.
Today, tungsten filament light bulbs routinely last for 750 hours.聽But in the offing is a bulb that has no filament and burns for over 10,000 hours!聽 The bulb is made of quartz and filled with argon and a small amount of sulphur.聽The sulphur atoms produce a stunning amount of light when excited by microwaves.聽Prototypes already light the Smithsonian Air and Space Museum in Washington but so far the bulbs are too bright for home use-shades of the arc lamp!
But perhaps the next time I'm driven from home by a power outage, the light that will glow on the porch welcoming me home will feature a sulphur bulb.聽For now, though, I'm just grateful for the old fashioned light bulb and the brilliance of Messieurs Davy, Faraday, Swan and Edison.
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