1224 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1951 



In July 1919 the continuing interest in this problem crystallized in a 

 Western Electric proposal to use permalloy continuous loading in new 

 transoceanic telegraph cables. Since this remarkable new magnetic alloy-^ 

 had been invented and developed by Western Electric engineers, they were 

 already familiar with its extraordinary high permeability characteristics, 

 and had confidence in their ability to use it in providing a high impedance 

 loading which would make practicable a great increase in message-carrying 

 capacity. Loading with iron-wire would not have any advantage in tele- 

 graph speed, because of its low permeability. Intensive research work 

 quickly started on the permalloy loaded cable design and installation prob- 

 lems, and on the related terminal apparatus and operating problems. The 

 success attained in these efforts resulted in disclosures to the Western Union 

 Telegraph Company regarding the great increase in telegraph signaling 

 speed that could be obtained with the proposed new permalloy loading. 

 In due course the Telegraph Company made arrangements with the Telegraph 

 Construction and Maintenance Company Ltd. of London for the manu- 

 facture and installation of a 120-mile trial length, using loading material 

 supplied by the Western Electric Company and applied and treated under 

 the direction of Western Electric engineers. In October 1923 this experi- 

 mental length was laid in deep water near the south shore of Bermuda. The 

 trial installation tests were so satisfactory that the Western Union company 

 arranged for the manufacture and installation of a 2300-mile cable to connect 

 New York with Horta in the Azores. As with the trial length, the loading 

 material was supplied by the Western Electric Company, and it was ap- 

 plied and treated under Western Electric supervision. 



The new cable was laid during September 1924. After refined adjust- 

 ments in the terminal apparatus, a speed of over 1900 letters per minute 

 was obtained. This speed is about four times the carrying capacity of an 

 ordinary non-loaded cable of the same length. At this point a brief state- 

 ment of general theory is indicated: The effect of the inductance is to 

 oppose the setting up of a current and to maintain it once it has been 

 established, thus preserving a definite wave front as the signal impulse 

 travels over the cable. The individuality of the signal impulses is retained, 

 and thus the much higher speed becomes possible. 



The permalloy loading material was applied in tape form in a close helix 

 around a stranded copper conductor. The tape was 0.006 inch thick and 

 0.125 inch wide. The alloy was composed of about 79% of nickel and 21% 

 of iron and a small amount of manganese, suitably heat treated. It provided 

 an inductance of about 54 millihenrys per mile, slightly over 12 times that 

 obtained by the use of iron wire in the Cuba cables previously described. 

 The permeability of the loading was about 2300, or about 20 times that of 



