502 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1915. 



The multiplex type of printing telegraph accromplishes this pur- 

 pose, and the present indications are that it will become the preferred 

 scheme for handling the heavy telegraph traffic which obtains be- 

 tween large cities. 



In the multiplex system the line is switched to each operator in 

 turn and at each switching the electrical signals, forming a one-letter 

 combination, are transmitted over the line. The switching mecha- 

 nism operates with such rapidity that it is possible to obtain a speed 

 of from 40 to 50 words per minute from each sending operator. 

 Thus in the case of a quadiiiple duplex — that is, a circuit trans- 

 mitting four messages in each direction- simultaneously over one 

 wire — the total carrying capacity of the circuit would be from 320 

 to 400 words per minute. 



In the multiplex system the messages are perforated on a paper 

 tape, as in the case of the high-speed systems, but instead of one 

 transmitting machine and one printing machine operating at a 

 high speed a number of separate transmitters and printers are used 

 at each end. These transmitter and printers a.re connected to the 

 switching mechanisms, and by means of properly designed syn- 

 chronizing apparatus the instruments at either end of the line are 

 kept in proper relation to one another, so that each printer is always 

 associated with its own transmitter. 



One great advantage of the multiplex from an electrical and me- 

 chanical standpoint lies in the relatively long time intervals which 

 obtain. Thus, after a letter combination has been sent out by a 

 transmitter to the distant printer, the transmitter has ample time to 

 set up another letter combination and the printer to print the letter 

 and to restore to normal before the machines are again connected 

 to the line. 



The multiplex printing telegraph system now being manufactured 

 by the Western Electric Co. has shown traffic loads per circuit aver- 

 aging nearly one-third greater than those carried by previous multi- 

 plex systems using the same number of operators. As compared with 

 high-speed systems, the traffic handled by this multiplex is probably 

 40 per cent greater per average circuit, although the number of 

 operators required is less. 



An outgrowth of the work on multiplex printers has been the 

 development of electrical printing mechanisms which bid fair to 

 have a wide field of application in other services, such, for example, 

 as in the operation of large commercial and manufacturing estab- 

 lishments. 



