Page:Popular Science Monthly Volume 88.djvu/404

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��'Popular Science Monthly

��tape with various combinations of holes. In the illustration the fresh tape may be seen unrolling from the reel back of the rack carrying the message about to be sent. After perforation at the left end of the keyboard machine, the tape passes under the pivoted arm of an automatic stop and then into a transmitter unit (at the extreme left of the photograph). The operator ordinarily punches tape at

���These eight operators work at one end of a single trunk line. Four are sending and four receiving, and they are kept busy every minute. The same number work on the other end of the wire, and it is possible to send more than six thousand messages over one wire in a single working day

��about the speed of transmission, so that a little slack tape hangs under the con- trol arm of the stopping device. Should he fall behind, however, as soon as the transmitter uses up the loose tape and so begins to stretch it tightly between the two machines, the control arm is lifted. This operation automatically stops both the local transmitter and the receiver at the distant end until more letters are perforated. Then the tape

��slackens, the control arm drops and transmission begins again. Thus the printed message appears complete and without blanks, even though the trans- mitting operator is forced to stop in the midst of perforating.

The printing receiver is shown in an- other photograph. Inside the case a message is being typewritten as the per- forated tape corresponding to it passes, letter by letter, through the transmitter. Each group of five impulses (one for each row of punched holes in the sending tape) prints a single letter, makes a space between words or starts a new line on the printed page by returning the pa- per-carriage to the right and turning up the paper. At the end of each mes- sage a short time is al- lowed for the receiving op- erator to take cut the printed telegram and in- sert a fresh blank; while the new message is being typed he checks over that which has just been re- ceived and, if it seems cor- rect, turns it over to the delivery department. ■

The printing, ready for delivery, of keyboard-per- forated messages, could be accomplished by any of the older successful page-print- ing telegraph systems. In fact, the same line could be duplexed and messages sent at about fifty words per minute in both direc- tions, so keeping four op- erators at work on a single wire. But the new printing telegraph is capable of handling the tele- graphic output of eight transmitters and thus keeping sixteen operators busy over one line. This simultaneous transmission of messages is made possible by the use of a pair of special distributors, one at each end of the line, which successively switch in and out each of four sets of in- struments. The line is duplexed and therefore permits messages to travel in both directions at the same time ; for each

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