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A.C. permeability resulting from the temporary application of large 

 magnetizing forces did not exceed 2 per cent as compared with changes 

 of the order of 30 to 40 per cent commonly found in previously available 

 materials. 



The next important step was the discovery of permalloy, a nickel- 

 iron alloy having extremely high permeability which had its first 

 application in the loading of submarine telegraph cables. This mate- 

 rial with its extremely low hysteresis loss and high induction for feeble 

 magnetizing forces, has since been applied extensively in the design of 

 transformers, relays, receivers, and other telephone apparatus. Fig. 15 



6000 



4000 



2000- 



-2000- 



-4000 



-6000 



-0.10 -0.8 -0.6 -0.4 -0.2 O 0.2 0.4 0.6 0.8 



H 



Fig. 15 — Hysteresis loops of silicon steel and permalloy. 



0.10 



shows comparative hysteresis loops for permalloy and silicon steel. 

 The much smaller hysteresis loss of permalloy, approximately one- 

 seventh of that of the silicon steel sample is indicative of its greatly 

 reduced tendency to remain magnetized after the removal of a mag- 

 netizing force, a property which is of great importance in the operation 

 of quick release types of relays. In transformers and in continuously 

 loaded cable, the very high permeability at small magnetizing forces 

 of this material, strikingly shown in Fig. 16, is of great value. It is the 

 high permeability of permalloy that made it possible to load telegraph 

 cables successfully and thereby attain a threefold increase in telegraph 

 speed. In transformers such as those used in vacuum tube amplifiers, 

 the high permeability permits the designer either to achieve equivalent 

 quality with a much smaller apparatus volume or, in the same space, 

 to furnish equipment of better quality. The latter result is shown by 

 the curves of Fig. 17 which indicate how transformer performance at 



