Some recent developments in photo-telegraphy and facsimile transmission

The paper deals with development work on which the authors have been engaged since 1945 on machines for the transmission of pictures and facsimiles over land-lines and radio. Faithful tone reproduction of photographic material has been attained, and machines have been produced to fulfil the needs of the Press. Machines with more precise scanning, up to 500 lines per inch, have been developed. A method of controlled retoning of a picture is also described. Further developments have been made using an electrochemical action instead of photographic paper as the recording medium. Machines have been produced to receive tone pictures and to act either independently or as monitors to the photographic machines. Recent applications of the electrochemical recorder to facsimile and telegraph purposes are described.