The Menlo Park research lab was made possible by the sale of the quadruplex telegraph that Edison invented in 1874. The quadruplex telegraph could send four simultaneous telegraph signals over the same wire. When Edison asked Western Union to make an offer, he was shocked at the unexpectedly large amount that Western Union offered; the patent rights were sold for $10,000. The quadruplex telegraph was Edison's first big financial success.
U.S. Patent #223898 Electric LampIn 1878, Edison formed Edison Electric Light Company in New York City with several financiers, including J.P. Morgan and the Vanderbilts. Edison made the first public demonstration of incandescent lighting on December 31, 1879, in Menlo Park. On January 27, 1880, he filed a patent in the United States for the electric incandescent lamp.
On October 8, 1883, the U.S. patent office ruled that Edison's patent was based on the work of William Sawyer and was therefore invalid. Litigation continued until October 6, 1889, when a judge ruled that Edison's electric light improvement claim for "a filament of carbon of high resistance" was valid. After he lost another court battle with Joseph Swan, he and Swan formed a joint company called Ediswan to market the invention. This company and its technological heritage became General Electric in 1892.
In 1880, Edison patented an electric distribution system. The first investor-owned electric utility was the 1882 Pearl Street Station, New York City. On January 25, 1881, Edison and Alexander Graham Bell formed the Oriental Telephone Company. On September 4, 1882, Edison switched on the world's first electrical power distribution system, providing 110 volts direct current (DC) to 59 customers in lower Manhattan, around his Pearl Street laboratory. On January 19, 1883, the first standardized electric lighting system employing overhead wires began service in Roselle, New Jersey.
U.S. Patent #223898 Electric Lamp
War of Currents era
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.During the initial years of electricity distribution, Edison's DC was the standard for the United States, and Edison was not disposed to lose all his patent royalties. During the "War of Currents" era, Nikola Tesla and Edison became adversaries due to Edison's promotion of DC for electric power distribution over the more efficient alternating current (AC) advocated by Tesla, who patented AC in Graz, Austria. Edison (or, reportedly, one of his employees) employed the tactics of misusing Tesla's patents to construct the first electric chair for the state of New York to promote the idea that AC was deadly. Popular myth has it that Edison invented the electric chair, despite being against capital punishment, solely as a means of impressing the public that AC was more dangerous than DC. In fact, like most of the output of the Menlo Park operations, the chair was primarily invented by a few of his employees, in particular Harold P. Brown, while Edison supervised their operations. 
Edison went on to carry out a campaign to discredit and discourage the use of AC. Edison presided personally over several electrocutions of animals, primarily stray cats and dogs, for the benefit of the press to prove that his system of DC was safer than that of AC. Edison's demonstrations peaked with the electrocution of Topsy the Elephant.
Many of Edison's inventions using DC ultimately lost favor to AC devices proposed by others. AC distribution systems replaced DC, extending the range and improving the safety and efficiency of power distribution. Since the 1950s, high-voltage direct current (HVDC) transmission systems have become more common in certain situations.
As exemplified by the light bulb, most of Edison's inventions were improvements of ideas by others, achieved through a diligent and industrial approach and team-based development. He was the undisputed head of the team, but usually did not share credit for the inventions. He himself said: "genius is one percent inspiration, ninety-nine percent perspiration." Nikola Tesla, possibly Edison's most famous employee who went on to be a great scientist and inventor in his own right, said about Edison's method of problem-solving: "If Edison had a needle to find in a haystack, he would proceed at once with the diligence of the bee to examine straw after straw until he found the object of his search. I was a sorry witness of such doings, knowing that a little theory and calculation would have saved him ninety percent of his labor." He profited from his good connections with Europe - European inventors often did not apply for US patents for their ideas, so that Edison was free to develop their ideas further himself and then obtain his own US patents.
Frank J. Sprague, a former naval officer, was recruited by Edward H. Johnson, and joined the Edison organization in 1883. Sprague was a good mathematician, and one of Sprague's significant contributions to the Edison Laboratory at Menlo Park was the introduction of mathematical methods. Prior to his arrival, Edison conducted many costly trial-and-error experiments. Sprague's approach was to calculate the optimum parameters and thus save much needless tinkering. He did important work for Edison, including correcting Edison's system of mains and feeders for central station distribution. 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.
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