Edison, Thomas Alva

US scientist and inventor, whose work in the fields of communications and electrical power greatly influenced the world in which we live. With more than 1,000 patents, Edison produced his most important inventions in Menlo Park, New Jersey 1876–87, including the phonograph. He obtained a US patent for the electric light bulb in 1879. He also constructed a system of electric power distribution for consumers, the telephone transmitter, and the megaphone.

Telegraphy and telephony
Edison's first success came in the area of telegraphy. Perceiving the need for rapid communications after the Civil War, his first invention was an automatic repeater for telegraphic messages. He then invented a tape machine called a ‘ticker’, which communicated stock exchange prices across the country.

Turning his attention to the transmission of the human voice over long distances in 1876, he patented an electric transmitter system that proved to be less commercially successful than the telephone of Bell and Gray, patented a few months later. Undeterred, Edison set about improving their system, culminating in his invention of the carbon transmitter, which so increased the volume of the telephone signal that it was used as a microphone in the Bell telephone.

The light bulb
While experimenting with the carbon microphone in the 1870s, Edison had toyed briefly with the idea of using a thin carbon filament as a light source in an incandescent electric lamp. He returned to the idea in 1879. His first major success came on 19 October of that year when, using carbonized sewing cotton mounted on an electrode in a vacuum (one millionth of an atmosphere), he obtained a source that remained aglow for 45 hours without overheating – a major problem with all other materials used. He and his assistants tried 6,000 other organic materials before finding a bamboo fibre that gave a bulb life of 1,000 hours. In 1878 English physicist Joseph Swan had also developed an electric lamp, and after a legal wrangle the joint company Edison and Swan United Electric Light Company came into being in 1883.

Generators and the first power stations
To produce a serious rival to gas illumination, a power source was required as well as a cheap and reliable lamp. The alternatives were either generators or heavy and expensive batteries. At that time, the best generators rarely converted more than 40% of the mechanical energy into electrical energy. Edison's first generator consisted of a drum armature of soft iron wire and a simple bi-polar magnet, and was designed to operate one arc lamp and some incandescent lamps in series.

A few months later he built a much more ambitious generator, the largest built to date, weighing 500 kg/1,103 lb and with an efficiency of 82%. Edison's team were at the forefront of development in generator technology over the next decade, during which efficiency was raised above 90%. To complete his electrical system he designed cables to carry power into the home from small (by modern standards) generating stations, and also invented an electricity meter to record its use.

The phonograph
In 1877 he began the era of recorded sound by inventing the phonograph, a device in which the vibrations of the human voice were engraved by a needle on a revolving cylinder coated with tin foil.