HIGH-SPEED OCEAN CABLE TELEGRAPHY 253 



direction of operation being controlled manually. While this type of 

 operation served well to carry the limited traffic then available, it 

 was not suited for efficient operation of the cable at its maximum 

 speed, both because of the practical difficulty of dividing the rapidly 

 received recorder tape among the three or more operators who would 

 be required to translate it, and because of the delays resulting from 

 manual control of reversal of direction. 



To make efficient use of a high-speed telegraph cable requires 

 some means of adapting it to the practical limitations of machines 

 and operators, preferably by the provision of a number of separate 

 channels of operation, each of which may be worked at a speed con- 



THE WESTERN ELECTRIC COMPANY 



FRESHEST EGGS AT BOTTOM MARKET PRICES 



SHE IS HIS SISTER 



Fig. 10 — Test message transmitted over New York-Horta cable at a speed of 1920 

 letters per minute, Nov. 14, 1924 



sistent with the pace of a single operator at each end of the cable. 

 With such multi-channel operation it is obviously necessary to provide 

 means for either simultaneous two-way working or automatic means 

 for direction reversal which shall not interfere with the independent 

 operation of the several channels. Also it is very desirable to provide 

 for automatically printing the received messages. 



There are two principal methods which have been used to secure 

 multi-channel operation with a single telegraph line — the carrier 

 current method and the multiplex distributor method. By the former 

 the separate channels are obtained by the modulation of separate 

 carrier frequencies in accordance with the telegraphic signals, the 

 line being simultaneously shared by all the channels; by the latter 

 the line is passed in rotation from one channel to the next so that the 

 line time is in effect divided equally among the several channels. 

 Either method or a combination of the two can be applied to a loaded 

 cable. The carrier current method has for several years been used 

 on the loaded cables of the Cuban-American Telephone Co. between 



