HIGH-SPEED OCEAN CABLE TELEGRAPHY 229 



For over fifty years the cable had remained substantially unchanged 

 in character, though great advances had been made in methods of 

 operation. Inductive loading, which was proposed by Heaviside in 

 1887, was the obvious means for obtaining increased cable speeds, 

 but no one had found a way to realize the advantages of loading as 

 applied to ocean cables. Loading with evenly spaced coils as proposed 

 by Pupin and used on land lines presented difficulties in laying and 

 maintenance which practically prohibited this method. Continuous 

 or Krarup loading by a wrapping of iron wire around the conductor of 

 the cable was mechanically feasible but the amount of inductance 

 which could be obtained in this way was not sufficient to justify its 

 use. In order to make continuous loading advantageous for long 

 ocean cables there was needed a material which could be much more 

 easily magnetized than iron. Fortunately we had at hand as an aid 

 to solving this problem the extraordinary magnetic material, permalloy, 

 an alloy possessing magnetic permeability many times that of iron, 

 even at the low magnetizing forces produced by the feeble currents of 

 a telegraph cable. It is on permalloy that the loaded cable depends 

 primarily for its success. 



Although permalloy provided the means to give the cable the 

 desired high inductance, the mere wrappmg of this metal around the 

 copper conductor of the cable was far from providing a practical 

 solution of the problem of high-speed ocean telegraphy. To achieve 

 this solution required the solution of very many subsidiary problems, 

 concerned not only with the making of a cable but also with the 

 transmission of signals over it and with the means for its practical 

 operation. Work on all these phases of the problem of the loaded 

 cable was actively pursued in our laboratories and in the field from 

 the time of the first proposal, made in July 1919, to load a trans- 

 oceanic cable with permalloy to the successful completion and opera- 

 tion of the New York-Horta cable. 



During the first two years of this period our investigations were 

 conducted wholly in the laboratory where hundreds of experimental 

 lengths of loaded conductors were made and tested to convince our- 

 selves that a permalloy-loaded cable could be manufactured and laid 

 successfully. During the same period studies of the signal distortion 

 of a loaded artificial cable and means for correcting distortion were 

 carried on. Simultaneously methods of high-speed operation of 

 loaded cables were developed, with the result that we were convinced 

 from our laboratory experiments, not only that a permalloy-loaded 

 cable could be made and laid successfully, but that it could also be 

 operated commercially at the high speeds which we had predicted. 



