Edison telephone, 1879.
© Science Museum / Science & Society Picture Library
The American scientist and inventor Thomas Alva Edison (1847-1931) redesigned the telephone shortly after its invention by Alexander Graham Bell (1847-1922) in 1876. He got around Bell's patents by inventing a carbon button transmitter, which became widely used, and a receiver called the motograph, which did not. The user had to turn the handle continuously to hear anything. This turning motion caused a diaphragm in the receiver to be tensioned by the friction created between a platinum strip and a revolving drum coated with damp chalk. Speech currents varied the friction and the tension, making the diaphragm produce sound. Edison was also the inventor of the phonograph and the electric light bulb.