Page:Popular Science Monthly Volume 88.djvu/402

 Typewriting Eight Telegrams Over

a Single Wire

��WHEN the possibilities of sending messages over a wire by elec- tricity were first realized, soon after Morse demonstrated the first tele- graph, the limitations in the message- carrying ability of a plain circuit were encountered. The ordinary good oper- ator could send only about one complete message per minute, and to do this he required the full use of a wire connect- ing him with the receiver. Each line was thus limited to about four hundred messages per business day, and it be- came clear that extremely high rates would have to be charged for messages over expensive long distance wires. The greatest cost of the telegraph system was due to the erection and maintenance of the lines, and therefore the best way to make lower charges possible appeared to be to increase the number of mes- sages which could be handled on each wire.

The first step toward solving the prob- lem of message limitation came with the duplex telegraph, which made it possible for four Morse operators to use a single wire at the same time. In this system two streams of messages pass over the wire simultaneously, in opposite direc- tions, so that the capacity is doubled. The next step was the quadruplex, in which four messages are sent simul-

��taneously, two in each direction, over the same wire. In this system one line carries about sixteen hundred messages per day, and large saving, as compared to plain or simplex single-message tele- graphing, results. The duplex and cjuad- ruplex are very greatly used today, and the latter is not easy to keep in full op- eration during rainy weather. An octu- plex system was devised, but has not been found practical.

Since the hand-telegraph systems are limited in message capacity by the speed of the Morse operator, automatic receivers and transmitters were de- vised to speed up the impulses passing over the line. In the Wheatstone sys- tem, which is perhaps the most success- ful of the plain automatic telegraphs, it is possible to send three hundred or four hundred words per minute over one wire, thus increasing the normal capac-- ity some ten or twelve times. In this system the messages are first pimched into special tapes by perforating oper- ators. The tapes which are simultane- ously punched out by ten perforators, will usually keep one wire in full oper- ation. At the receiving station the mes- sages are printed in dots and dashes on a second tape ; this is divided into suit- able lengths and distributed amongst a number of transcribing operators who

���This remarkable telegraph system has been in operation over the lines shown for many months, and has resulted in the saving of much time and money to the company, and

eventually to the senders

374

�� �