192 ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 7 



Duplex telegraphy was invented by the president of the Franklin 

 Telegraph Co. in 1872. This allowed simultaneous sending and re- 

 ceiving at each end of the circuit, doubling the circuit capacity. The 

 Western Union purchased this patent, then made arrangements with 

 Thomas A. Edison to see if any latent possibilities could be developed. 



After considerable experimenting, Mr. Edison invented the Quad- 

 ruplex. This method allowed two simultaneous sendings in each 

 direction. The single circuit capacity had now been increased four- 

 fold. 



The Wheatstone siphon recorder, an English invention, was brought 

 to this country in 1883 and was used extensively on the earlier cable 

 circuits. It was soon replaced on land lines by a faster type Wheat- 

 stone recorder. An inked wheel marked the dots and dashes upon a 

 rapidly moving strip of paper. Signals from both of these systems 

 were transmitted from perforated tape. The recorder could handle 

 about 90 words per minute, but it was necessary to translate the tape 

 and write the message on a blank. 



During the period 1901 to 1910, many printing telegraph systems 

 were developed. The better known were the House system which 

 printed on a strip of paper and the Buckingham system which printed 

 directly on a message blank. 



The Barclay system was developed from Buckingham patents about 

 1904-05 and was the first printer to stand up under heavy traffic. It 

 would handle about 50 words per minute but required frequent and 

 careful adjustment of the selecting mechanism. It was soon re- 

 placed by the Morkrum-Kleinschmidt printer, an invention of Howard 

 Krum of Chicago. 



About 1912 the Western Union-developed page printer had been 

 installed on the heavier circuits between New York and San Fran- 

 cisco. The first printer had a stationary carriage and movable type 

 wheel. Later on, a type bar printer was developed which used the 

 Baudot code system and is now being used in conjunction with the 

 Multiplex. The present 21-A tape printer will handle 72 words per 

 minute with average maintenance whereas the earlier printers re- 

 quired continual adjusting. 



It was soon found that the line- wire circuit was capable of carrying 

 signals much faster than a single operator could send them or faster 

 than a single receiving printer could print them, clear the selecting 

 mechanism and be ready for a second incoming signal. In order to 

 make full use of the circuit, it was necessary to develop a method which 

 could handle signal impulses to the full capacity of the circuit. This 

 system is known as the Multiplex and is used throughout our system 

 to handle the major portion of trunk-line traffic. 



The Multiplex divides the use of the circuit among a number of 

 channels. The sending distributor picks up signals from the trans- 



