264 BELL SYSTEM TECHNICAL JOURNAL 



Even if it could be shown that all of the apparent objections to 

 coil-loading could be overcome, I think it is highly improbable that 

 coil-loading would be resorted to for long deep-sea telegraph cables. 

 Continuous loading has been given a practical trial and has proved 

 successful and does not add greatly to the cost of a cable. Coil- 

 loading involves risks which there is now no need to assume and its 

 economic advantage, if any, is certainly small in proportion to the 

 whole cost of a cable installation. 



Though continuous loading as applied in several particular instances 

 has been successful, there is no occasion to assume that the develop- 

 ment of the art of continuous loading is completed. Modifications in 

 continuous loading can be introduced with relatively little risk and 

 are justified if an economic advantage can be shown. Also cable 

 construction, apart from the loading, may be modified so as to realize 

 more completely the advantages which loading affords. It is therefore 

 of interest to consider some of the ways in which continuously loaded 

 cables of the future might be different from those of the present. 



Loading materials can be produced with different magnetic prop- 

 erties and to a limited extent the resistivity of alloys may be altered 

 by control of composition. Higher permeability is not necessarily 

 desirable since with increased permeability goes also increased 

 effective resistance due to energy losses in the permalloy. In the 

 case of any particular cable with practical limitations of dimen- 

 sions, materials and costs there is an optimum permeability which, 

 in general, is lower the higher is the frequency for which the cable is 

 designed. Short cables designed for very high frequencies will 

 accordingly require lower permeability than has been required for the 

 long cables which have been made. For cables of all lengths and 

 speeds a high degree of constancy of magnetic permeability with 

 regard to magnetizing force is desirable. With the New York-Horta 

 cable the inductance increases about 50 per cent when the current 

 is increased from 0.001 to 0.1 ampere. The relative increase is less 

 for some of the later cables, owing to improvements in loading. A 

 loading material of high electrical resistivity is, of course, always 

 advantageous. 



There are other ways of applying continuous loading than that of 

 Krarup. For example, the magnetic material may be electroplated 

 onto the conductor. Such modifications may eventually come into use 

 but the need for them does not appear to be great in the case of long 

 deep-sea cables and there is not much economic incentive for their 

 development. Accordingly I do not believe that changes of this 

 type are likely to alter greatly the possibilities of submarine cables 

 for telegraphy over long distances. 



