Thomas Alva Edison is considered one of the greatest inventors in history. He was born in Milan, Ohio on February 11, 1847 and died in 1931. During his life he patented 1,093 inventions. Many of these inventions are in use today and changed the world forever. Some of his inventions include telegraphy, phonography, electric lighting and photography. His most famous inventions were the phonograph and the incandescent light bulb.
             Edison did some of his greatest work at Menlo Park. While experimenting on an underwater cable for the automatic telegraph, he found that the electrical resistance and conductivity of carbon varied accordingly to the pressure it was under. This was a major theoretical discovery, which enabled Edison to invent a "pressure relay" using carbon rather than magnets, which was the usual way to vary and balance electrical currents. In February of 1877 Edison began experiments designed to produce a pressure relay that would amplify and improve the audibility of the telephone, a device that Edison and others had studied but which Alexander Graham Bell was the first to patent, in 1876. By the end of 1877 Edison had developed the carbon-button transmitter that is still used today in telephone speakers and microphones.
             Many of Thomas Edison's inventions including the carbon transmitter were in response to demands for new products and improvements. In 1877, he achieved his most unique discovery, the phonograph. During the summer of 1877 Edison was attempting to devise for the automatic telegraph a machine that would transcribe a signals as they were received into a form of the human voice so that they could then be delivered as telegraph messages. Some researchers had theorized that each sound, if it could be graphically recorded, would produce a distinct shape resembling short hand, or phonography, as it was known then. Edison hoped to make this concept real by employing a stylus-tipped carbon transmitter...