[D0106AAP], Letter from John F Ott to William Edgar Gilmore, July 29th, 1901
https://edisondigital.rutgers.edu/document/D0106AAP
Transcription
Mr. Gilmore The block signal I have worked up and it is an easy thing to do, there are three way to do it, all are extremely simple. If you will get me two set of telephones complete with two head telephone receivers such as used in central stations. Get long distance desk set. I can make model in about four days complete. July 29, 1901