A GOOD IDEA AT THE TIME ....

THE EDISON EFFECT

In 1883 Edison was engaged in improving his electric light bulbs, but was troubled by blackening on the inside of the bulb. The British Scientist Sir William Crookes, who was working for Edison in London, deduced that this was caused by an electron beam from the filament, a condition which became known as 'The Edison Effect'. This was put to good use by Sir Ambrose Fleming who found that electrons could only flow in one direction, and adding another electrode would create a diode which he could use to rectify wireless signals. These electron beams were also known as cathode rays, and in 1897 Professor Braun described a method of focussing and deflecting them with the ultimate aim of electronic picture scanning. The first proposal for a cathode ray tube was patented by Professor Dieckman in Germany, but the missing element was some means of amplifying the extremely weak signals.

In America about this time Dr Lee De Forest was experimenting with Fleming's diode, adding a third electrode which was perforated in an attempt to control the electron flow. He was completely successful and in 1905 applied for a patent for his 'Audion' vacuum tube, which could also amplify speech signals. This invention enabled a voice to modulate a transmitter for the first time. World War One put a stop to any further television activity, but great strides were made in the development of vacuum tubes. Regular sound broadcasting was commenced in 1920, but electronic television remained just a collection of ideas.

Working for EMI in the early 1930's was an emigre from Russia, Isaac Schoenberg, who constructed a camera tube called the 'Emitron', which was similar to the RCA 'Iconoscope' developed by his fellow countryman VK Zworykin. Inside a glass envelope was an electron gun emitting cathode rays which were deflected to scan a light sensitive mosaic screen behind a camera lens. This enabled the BBC to commence regular television broadcasts on November 2nd- 1936, using the EMI/Marconi electronic system giving 405 lines and the Baird -mechanical system giving 240 lines on alternate weeks. After a trial period it became obvious that the electronic system gave superior results, and the Baird system was dropped. Three years later RCA commenced television broadcasts from the Empire State Building, using their Iconoscope camera. The Edison Effect has certainly been put to good use!

JOHN ALDRED