1088 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



lines. (The record does not disclose why one of the terminals of the system 

 could not be assigned.) It used a rotary selector per line directly driven 

 by a single train of pulses generated by a lever operated dial at the sta- 

 tion. The selector had 100 points and the number of pulses sent corre- 

 sponded to the number of the called line. The 20-line system was similar 

 to the 100-line system. 



The Clark system was a single motion rotary step-by-step system 

 using 75-point switches which accommodated a maximum of 74 lines. 

 (Here again there is no record as to why one terminal was not used for 

 a line.) It did not provide a busy test. There were no relays in this 

 system. 



"automatic operator" SYSTEMS 



The Faller and the Lorimer systems were called "automatic operator" 

 systems but they were actually versions of direct dial. The Faller system 

 was apparently never used commercially, but the Lorimer system was. 



The inventors of the Lorimer system had several objectives. One was 

 to produce a system which could be installed in 100-line building blocks, 

 called sections. As little as one section could be installed and operated 

 alone. Additional sections in increments of 100-line capacity could be 

 added as required up to the limit ot 10,000 lines. Another object was to 

 get good contacts and they therefore employed switches with heavy 

 contacts like those used in power switches. The power needed to drive 

 switches with such contacts led to the adoption of a common power 

 drive for a number of switches instead of electromagnets individual to 

 the switches. Still another aim was to provide a minimum of equipment 

 on a per line basis and to provide equipment only to the extent required 

 by traffic. Line relays were therefore omitted in early offices and the 

 100-line sections were divided into divisions, maximum 10 divisions per 

 section, with arrangements for omitting divisions if not required by 

 traffic. 



The Lorimer system was a direct dial system operated from a pre-set 

 calling device. It had a line finder stage, a selector stage and a con- 

 nector stage. The calling device, wound up by a crank, had four settable 

 levers, one for each digit, each of which grounded one terminal in its 

 own set of ten terminals corresponding to the digit set up. The levers 

 also operated a visual indicator. In the calling device there was also a 

 switch driven over its terminals by a magnet-controlled escapement. 

 Pulses were sent from the central office to control the escapement and 

 the central office equipment was driven in synchronism with the station 



