Q: ALISTAIR Cooke, in his Letter from America, said that Thomas Edison invented the electric light bulb. I understood that it was Sir Joseph Swan of Newcastle. - Mary Ellery, Peterlee.

A: AMERICA'S Thomas Edison (1847-1931) was one of the greatest inventive geniuses. During his lifetime, he took out 1,093 patents, but he did not invent the light bulb - the thing for which he is most famed.

Edison had a knack for developing and improving the work of others. His three greatest inventions were the phonograph, motion pictures and the electric light bulb. His phonograph relied on a sheet of tin foil placed over a cylinder, which recorded sound with the aid of a needle. The sound recorded on the foil could only be played a few times before it was lost. Other inventors developed permanent phonographic records at a later date.

Edison's most famous invention is the electric light bulb, which he 'invented' and patented in 1879. Unfortunately for Edison, in the previous year, the Sunderland-born chemist Joseph Swan (1828-1914) invented and patented virtually the same light bulb. Swan's findings were published in the US journal Scientific America and Edison was almost certainly a reader of this publication. Edison made a slight improvement, replacing Swan's carbon filament with bamboo, but to all intents and purposes, it was Swan's invention.

Swan's invention and development of electric light goes back long before 1878. In the early 1860s he developed a light bulb but it was abandoned due to the lack of a suitable vacuum pump for removing air from the glass. An improved vacuum pump developed by the German inventor Herman Sprengel allowed Swan to restart the experiments in the 1870s. He made his first demonstration to the public at Newcastle in February 1879, some ten months before Edison's first demonstration.

Both men sued each other but Edison, despite removing crucial evidence from his notebooks, lost the case. As a result, Swan was given a major share in Edison's electric company which was renamed Edison Swan United Electric Company in acknowledgement of Swan's work. Edison was very successful in promoting the widescale use of electric light through his General Electric company in the States, which helped to perpetuate the myth that he was the inventor of the electric light bulb.

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