Lee De Forest invented the audion, a vacuum tube device that could take a weak electrical signal and amplify it into a larger one. The audion helped AT&T set up coast-to-coast phone service, and it was also used in everything from radios to televisions to the first computers. The audion, or triode, at the heart of the vacuum tube is what the transistor was built to replace after 40 years.
De Forest got his Ph.D. in Physics from Yale in 1896. He began tinkering and inventing things even in high school, often trying to build things that he could sell for money. By the time he died he had over 300 patents, but few of them ever met with much success. In fact, De Forest seems almost to have had a nose for failure. He was regularly involved in patent lawsuits (indeed, he spent his fortune on legal bills). He went through four marriages, had a number of failed companies, was defrauded by his business partners, and was even once indicted (but later acquitted) for mail fraud.
With the audion, however, De Forest had a solid success. De Forest has been labeled “father of radio” and the “grandfather of television”, since the audion helped start the explosion of electronics earlier this century. De Forest invented the device in 1906, by inserting a grid into the center of a vacuum tube. Applying voltage to the grid controlled the amount of a second current flowing across the tube. In 1913, AT&T installed audions to boost voice signals as they crossed the US continent. Soon the audion was being used in radios as well.
In 1921, De Forest invented a way of recording sound on movies. He started a company, the De Forest Phonofilm Corporation, but he couldn’t convince the film industry to try using sound. Paradoxically, within a few years’ time, the motion-picture industry converted to talking pictures by using a sound-on-film process similar to de Forest’s.