HIGH-SPEED OCEAN CABLE TELEGRAPHY 233 



current loss. The resistivity of the whole nickel-iron series of alloys 

 is higher than that of either iron or nickel. By adding a third element, 

 for example chromium, to the nickel and iron and keeping the ratio of 

 nickel to iron about 4 : 1, a combination of very high resistivity and 

 very high initial permeability may be obtained in the same alloy. 



The permalloy used in the New York-Horta cable contained about 

 79 per cent nickel and 21 per cent iron with a small amount of manga- 

 nese to make it more malleable. The permeability of this alloy as 

 used on the New York-Horta cable was about 2300, its resistivity 

 being about 16 microhm-cms. On the Horta-Emden cable, the New 

 York-Bay Roberts-Penzance cables and the Fanning Island-Suva 

 cable permalloy containing about 80 per cent nickel, 17.5 per cent 

 iron, 2 per cent chromium and 0.5 per cent manganese was used. 

 With this alloy an initial permeability of about 3700 was obtained. 

 Its resistivity is about 38 microhm-cms. 



The permalloy loading material used on the New York-Horta cable 

 was in the form of a thin tape 0.006 inch (0.015 cm.) thick and 0.125 

 inch (0.32 cm.) wide applied in a closely wound helix surrounding the 

 conductor. On the Horta-Emden cable tape 0.0059 X 0.098 inch 

 (0.015 X 0.25 cm.) was used. On the New York-Bay Roberts and 

 Bay Roberts-Penzance cables the tape thickness was 0.0055 inch 

 (0.014 cm.) and the widths were 0.079 inch (0.20 cm.) and 0.123 

 inch (0.31 cm.) respectively. On the Fanning Island-Suva cable the 

 permalloy is in the form of a wire of 0.011 inch (0.028 cm.) diameter 

 applied in a single closely laid helix. The northern section of the 

 Pacific cable from Bamfield to Fanning Island is reported ^ to be loaded 

 similarly with "Mumetal" wire of 0.010 inch diameter, made by the 

 Telegraph, Construction & Maintenance Company. 



Very good results have been obtained with both tape and wire 

 loading. The tape has the advantages of costing less to apply and of 

 possessing greater mechanical strength, whereas the wire has the 

 advantages of lower eddy-current loss and of being less affected by 

 the earth's magnetic field. With either wire or tape loading the 

 component of the earth's magnetic field parallel to the cable sets up 

 magnetic induction in the helical loading material and consequently 

 reduces its effective permeability for the small magnetizing forces of the 

 signalling current. This reduction of effective permeability by the 

 earth's magnetic field is greater, the greater the angle of lay with 

 which the loading material is applied. Consequently this effect is 

 generally greater with tape loading than with wire loading. Whether 



2E. S. Heurtley, Electrician, Vol. 98, pp. 348-350, Apr. 1, 1927. See also P. 0. 

 Elec. Engrs. Jl., Vol. 20, pp. 36-40, Apr. 1927. 



