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Edison speech on light bulb (file info)
Video clip of Thomas Edison talking about the invention of the light bulb, late 1920s.
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Carbon telephone transmitter
In 1877 and 1878 Edison invented and developed the carbon microphone used in all telephones along with the Bell receiver until the 1980s. After protracted patent litigation, a federal court ruled in 1892 that Edison and not Emile Berliner was the inventor of the carbon microphone. (Josephson, p146). The carbon microphone was also used in radio broadcasting and public address work through the 1920s.


War of currents
Main article: War of Currents

Extravagant displays of electric lights quickly became a feature of public events, as this picture from the 1897 Tennessee Centennial Exposition shows.Nikola Tesla and Edison became adversaries due to Edison's promotion of direct current (DC) for electric power distribution over the more easily transmitted alternating current (AC) system developed by Tesla and sold by George Westinghouse. Unlike DC, AC could be stepped up to very high voltages with transformers, sent over thinner wires, and stepped down again at the destination for distribution to users.

Despite Edison's contempt for capital punishment, the war against AC led Edison to become involved in the development and promotion of the electric chair as a demonstration of AC's greater lethal potential versus the "safer" DC. Edison went on to carry out a brief but intense campaign to ban the use of AC or to limit the allowable voltage for safety purposes. As part of this campaign, Edison publicly electrocuted dogs, cats, and in one case, an elephant[6] to demonstrate the dangers of AC. Tesla's AC replaced DC in many instances of generation and power distribution, enormously extending the range and improving the safety and efficiency of power distribution. Though widespread use of DC ultimately lost favor for distribution, it exists today primarily in long-distance high-voltage direct current (HVDC) transmission systems. Low voltage DC distribution continued to be used in high density downtown areas for many years and was replaced by AC low voltage network distribution in many central business districts. DC had the advantage that large battery banks could maintain continuous power through brief interruptions of the electric supply from generators and the transmission system. Rectifiers supplied to convert the low voltage AC to DC for such DC load as elevators, fans and pumps. There were still 1600 DC customers in downtown New York City when the service was discontinued in 2005.


Work relations
Frank J. Sprague, a competent mathematician and former naval officer, was recruited by Edward H. Johnson, and joined the Edison organization in 1883. One of Sprague's significant contributions to the Edison Laboratory at Menlo Park was to expand Edison's mathematical methods. (Despite the common belief that Edison did not use mathematics, analysis of his notebooks reveal that he was an astute user of mathematical analysis, for example, determining the critical parameters of his electric lighting system including lamp resistance by a sophisticated analysis of Ohm's Law, Joule's Law and economics.) A key to Edison's success was a holistic rather than reductionist approach to invention, making extensive use of trial and error when no suitable theory existed. (See Edisonian approach). Since Sprague joined Edison in 1883 and Edison's output of patents peaked in 1880 it could be interpreted that the shift towards a reductionist analytical approach may not have been a positive move for Edison. Sprague's important analytical contributions, including correcting Edison's system of mains and feeders for central station distribution, form a counter argument to this. In 1884, Sprague decided his interests in the exploitation of electricity lay elsewhere, and he left Edison to found the Sprague Electric Railway & Motor Company. However, Sprague, who later developed many electrical innovations, always credited Edison for their work together.

Another of Edison's assistants was Nikola Tesla who claimed that Edison promised him $50,000 if he succeeded in making improvements to his DC generation plants. Several months later, when he had finished the work and asked to be paid, Tesla claimed that Edison said, "When you become a full-fledged American you will appreciate an American joke"[7]. Tesla immediately resigned. This anecdote is somewhat doubtful, since at Tesla's salary of $18 per week the bonus would have amounted to over 53 years pay, and the amount was equal to the initial capital of the company. Tesla resigned when he was refused a raise to $25 per week (Jonnes, p110). Although Tesla accepted an Edison Medal later in life and professed a high opinion of Edison as an inventor and engineer, he remained bitter. The day after Edison died the New York Times contained extensive coverage of Edison's life, with the only negative opinion coming from Tesla who was quoted as saying, "He had no hobby, cared for no sort of amusement of any kind and lived in utter disregard of the most elementary rules of hygiene" and that, "His method was inefficient in the extreme, for an immense ground had to be covered to get anything at all unless blind chance intervened and, at first, I was almost a sorry witness of his doings, knowing that just a little theory and calculation would have saved him 90 per cent of the labor. But he had a veritable contempt for book learning and mathematical knowledge, trusting himself entirely to his inventor's instinct and practical American sense." When Edison was a very old man and close to death, he said, in looking back, that the biggest mistake he had made was that he never respected Tesla or his work.


Media inventions
The key to Edison's fortunes was telegraphy. With knowledge gained from years of working as a telegraph operator, he learned the basics of electricity. This allowed him to make his early fortune with the stock ticker, the first electricity-based broadcast system. Edison patented the sound recording and reproducing phonograph (or gramophone in British English) in 1878. Edison also holds the patent for the motion picture camera, although the invention itself was the work of Edison's British employee, William Dickson. In 1891, Thomas Edison built a Kinetoscope, or peep-hole viewer. This device was installed in penny arcades, where people could watch short, simple films.

On August 9, 1892, Edison received a patent for a two-way telegraph. In April 1896, Thomas Armat's Vitascope, manufactured by the Edison factory and marketed in Edison's name, was used to project motion pictures in public screenings in New York City. Later he exhibited motion pictures with voice soundtrack on cylinder recordings, mechanically synchronized with the film. In 1908 Edison started the Motion Picture Patents Company, which was a conglomerate of nine major film studios (commonly known as the Edison Trust). Thomas Edison was the first honorary fellow of the Acoustical Society of America, which was founded in 1929.


Later years

Edison celebrates his 82nd birthday with President Herbert Hoover, Henry Ford, and Harvey Firestone. Ft. Myers, Florida, February 11, 1929.Edison became the owner of his Milan, Ohio, birthplace in 1906, and, on his last visit, in 1923, he was shocked to find his old home still lit by lamps and candles. Influenced by a fad diet that was popular in the day, in his last few years "he consumed nothing more than a pint of milk every three hours".[9] He believed this diet would restore his health.

Edison was active in business right up to the end. Just months before his death in 1931, the Lackawanna Railroad implemented electric trains in suburban service from Hoboken to Gladstone, Montclair and Dover in New Jersey. Transmission was by means of an overhead catenary system, with the entire project under the guidance of Thomas Edison. To the surprise of many, Thomas Edison was at the throttle of the very first MU (Multiple-Unit) train to depart Lackawanna Terminal in Hoboken, driving the train all the way to Dover. As another tribute to his lasting legacy, the very same fleet of cars Edison deployed on the Lackawanna in 1931 served commuters until their retirement in 1984. A special plaque commemorating the joint achievement of both the railway and Edison, can be seen today in the waiting room of Lackawanna Terminal in Hoboken, presently operated by New Jersey Transit.

Edison purchased a home known as "Glenmont" in 1886 as a wedding gift for Mina in Llewellyn Park in West Orange, New Jersey. The remains of Edison and his wife, Mina, are now buried there. The 13.5 acre (55,000 m²) property is maintained by the National Park Service as the Edison National Historic Site. Thomas Edison died on October 18, 1931, in New Jersey at the age of 84. His final words to his wife were "It is very beautiful over there."[10] Mina died in 1947. Edison's last breath is purportedly contained in a test tube at the Henry Ford Museum. Ford reportedly convinced Charles Edison to seal a test tube of air in the inventor's room shortly after his death, as a memento. A plaster death mask was also made.