408 BELL SYSTEM TECHNICAL JOURNAL 



end with each one of a number of transmitters in rotation by means of 

 a rotating brush which passes over a segmented commutator to which 

 the transmitters are connected as illustrated in Fig. 3. In this figure 

 the commutator segments are shown developed for sake of simplicity. 

 At the receiving end, the line is similarly associated in rotation with 

 each one of a corresponding number of printers by means of the 

 receiving brush and commutator. The commutator brushes at the 

 two ends of the line are maintained in nearly exact synchronism by 

 short correcting impulses which are derived from reversals in the 

 received signalling currents, and their phase relation is such that each 

 of the five segments connected with the "A " channel transmitter will 

 be connected in rotation through the line to the corresponding segments 

 of the "A" channel printer once during each revolution of the brushes, 

 and the impulse transmitted from any one sending segment will pass 

 through the corresponding receiving segment and operate the printer 

 selector magnet which is connected to it. Similarly the transmitter 

 on each of the other channels will be connected to its corresponding 

 printer once during each revolution of the brushes. The commutators 

 and the associated brushes together with the mechanism provided for 

 correcting the phase relation of the brushes are usually referred to as 

 distributors. 



In the operation of this system a transmitting tape is prepared in 

 which the characters to be transmitted are represented by combinations 

 of holes perforated in the tape by means of a keyboard perforator 

 which resembles a typewriter. The tape thus prepared is drawn 

 through a transmitter which is arranged to apply to its associated 

 distributor segments, positive and negative battery in the proper 

 combination to form the five-unit impulses corresponding to the 

 perforations in the tape. The received signal combinations control 

 the operation of an automatic telegraph typewriter or printer which 

 converts the signals into printed characters. Detailed descriptions of 

 the perforating, transmitting and printing apparatus and the various 

 methods for maintaining synchronism used in the multiplex system 

 are given in the paper by Mr. J. H. Bell, previously referred to, and 

 also in an excellent book by Mr. H. H. Harrison entitled "Printing 

 Telegraph Systems and Mechanisms." 



On account of the many advantages which this system embodied, 

 it was chosen in principle as a basis for the development of the new 

 system, although in several important respects much of the apparatus 

 and operating methods employed were entirely unsuitable for loaded 

 cable operation. The multiplex had been employed almost entirely in 

 the operation of duplexed circuits and therefore was not applicable to 



