This folder contains correspondence relating to Edison's work on a hearing aid. Following the appearance of articles about the phonograph which drew attention to his own deafness, Edison began receiving inquiries about inventing a hearing aid. By the middle of May 1878 Edison had turned his attention to the problem and began answering these letters with a standard response which appears to have become the basis for a "sound circular." By the end of the month this circular was being sent in answer to an ever increasing number of inquiries, as news of the invention spread through the newspapers. No copies of the sound circular have been found at the Edison National Historical Park.
All correspondence from March through May has been selected. Many of the letters contain marginalia providing information about Edison's work on the hearing aid and about his own deafness. Because of the voluminous nature of the rather routine inquiries which begin in June, only correspondence from significant individuals and letters containing substantial marginalia have been selected. The unselected material consists of about 600 individual pieces of correspondence. Approximately 80 percent of the letters are from the United States. Of the American letters, nearly 50 percent are from the Northeast, primarily from New York and Pennsylvania; more than 25 percent are from the Midwest; more than 20 percent are from the South; and less than 1 percent are from the West. Of the foreign letters, more than 80 percent are from Canada, Great Britain, and Germany. Courtesy of Thomas Edison National Historical Park.