Lee de Forest, American electrical engineer and inventor, c 1936.
© Science Museum / Science & Society Picture Library
De Forest (1873-1961) was principally known for his invention of the Audion in 1906. The Audion was a vacuum tube device that could take weak telegraph or radio signals and amplify them. Soon audions were being used in radios and and were installed to boost voice signals as they crosed the US continent. In 1921 De Forest also contributed to the film industry when he used electricity to improve sound recordings. This achievement led directly to the creation of motion picture with sound. Photograph by Joseph Capitaine.