320 : The Atlantic 



wait their turn for transmission. These difSculties were gradually 

 overcome and once the success of the cable had been demonstrated 

 the use of cable services expanded rapidly. 



A great forward step which increased the rate of transmission and 

 therefore the value of any cable was taken in 1871 with the invention 

 of the duplex cable system. This made it possible to send messages in 

 two opposite directions simultaneously. The duplex system was later 

 replaced by the multiplex system and a whole succession of improve- 

 ments in the pattern of cable construction permitted the transmis- 

 sion simultaneously of a great number of messages in each direction. 

 The old-fashioned sending and receiving equipment has also over the 

 years been replaced by complicated coding and decoding devices and 

 by the use of instruments for printing out, on a continuous tape, a 

 succession of messages. The whole process is now largely automatic 

 from the typing of a message from one end of the line to its recep- 

 tion, in typed form, at the other end of the line where the tapes are 

 cut into their component messages, mounted on an appropriate form 

 and delivered to the addressee. 



The islands of the Atlantic have naturally become an important 

 asset to the cable companies. At Horta, in the Azores, there is an 

 important center from which cables radiate to northern Europe, 

 southern Europe, Africa, North America and South America. This 

 station has been in continuous operation for many years and through 

 a succession of wars. The station is jointly maintained by several 

 companies and messages are relayed from one service to another. 

 Hundreds of automatic machines are in continuous operation and 

 the personnel which handles this enormous flow of traffic is surpris- 

 ingly limited. 



Some idea of the volume and importance of the cable business can 

 be ascertained from the following brief summary of facts: In 1925 

 there were twenty-one cables operating across the Atlantic Ocean 

 alone. In all parts of the world there are 3,000 separate submarine 

 cables; these account for 300,000 miles of submarine cable. Present- 

 day submarine cable weighs about two tons per nautical mile. How- 

 ever, cables have to be protected as they reach shallow water and the 

 anchorage ashore and this, naturally, increases their weight. The 

 shoreward end of a cable may reach a weight of thirty tons per nau- 

 tical mile. 



One might suppose, once a cable had been carefully laid down 

 over the ocean floor and the two ends carefully secured at shore sta- 

 tions, that for a long period of time the cable would be safe and 



