These documents cover the period February-May 1878. They consist of three letters by Edison to Henry Edmunds, Jr., a British engineer who had met Edison while on a trip to the United States in 1877. The correspondence relates primarily to the development of Edison's phonograph and telephone and to the attempts to promote these inventions in Europe. One letter concerns the controversy between Edison and British inventor David E. Hughes over who was the first to discover that carbon and other semiconductors vary their resistance under pressure.