Carrier telegraph systems

IN THE TIME of Samuel F. B. Morse, inventor of the telegraph, a single telegraph transmission of perhaps five words per minute represented the maximum use that could be made of a telegraph wire. Today over 97 per cent of all telegraph communication in the United States is carried on by automatic printers, which are known as teleprinters or teletypewriters. The word-per-minute speed of such machines is 60, and as many as 144 of these machines are now worked over a two-wire pair. The relative wire economies of the modern system and that in use even relatively recently, when the telegraph sounder still clicked away its 20 words per minute, are obvious.