462 BELL SYSTEM TECHNICAL JOURNAL 



molybdenum. As a rule the maximum permeability was generally 

 decreased when a non-magnetic element was added and so were the 

 saturation values of induction. 



As our investigation was undertaken primarily for the purpose of 

 searching for magnetic materials which could be used to advantage 

 in the electrical communication field, it may be of interest to describe 

 a few of the principal uses to which some of these alloys have been put. 



Of the three groups of alloys which are of special technical interest, 

 the permalloys are now used extensively in electrical communication 

 circuits. Perhaps its most spectacular use is for continuous loading of 

 submarine telegraph cable. 



The term loading is used in the electrical communication art to 

 designate a system of adding inductance to a transmission circuit for 

 the purpose of overcoming the unfavorable transmission characteristics 

 resulting from the electrical capacity of the circuit. This system has 



PERMALLOY 

 LOADING TAPE 



Fig. 21 — Sample of submarine loaded cable, showing the loaded conductor. 



been used in telephone transmission circuits for over a quarter of a 

 century. The standard method used for telephone circuits, in which 

 inductance coils are placed at equally spaced intervals along the trans- 

 mission line, was not considered practical for deep sea cables. The 

 only suitable method from a mechanical standpoint was a continuous 

 loading in which a magnetic material is distributed uniformly along 

 the whole length of the cable. Before permalloy was developed the 

 best magnetic material available was iron. It could not be used 

 economically for long submarine cables because of its low permeability. 

 With permalloy having between 40 and 50 times the permeability of 

 iron in the range of magnetic field strength encountered in such cables, 

 it was found that beneficial results could be attained and cables of 

 more than five times the carrying capacity of the old type could be 

 built. 



The first permalloy loaded submarine telegraph cable was laid in 

 1924 between New York and the Azores, a distance of approximately 

 2,300 nautical miles. A sample of the deep sea section of this cable 



