i.o.inixc I'oR ■//■j.iU'iio.M'. ciRcriis 270 



loaded sul)niariiu' caljles is exrellcnl, tluis dcmonstratini; a salistactory 

 solution of the many difficult mechanical problems involved. 



Continuous Loading. Another form of sul)marine cable loadinK^ 

 first i)ut into practise by the Danish engineer, T. E. Kraruii,-'" is to 

 wind an iron wire or tape spirally arf)und the copper conductor. This 

 c;i\-es a continuous loading which has found important applications 

 in the case of telephone and telegraph cables lai<l in deep water. So 

 far as land cables are concerned, it has been found that continuous 

 loading is uneconomical in comparison with coil loadmg. The only 

 instances of continuous loading in the plant of the Bell System are the 

 Florida-Cuba cables,''' connecting Key West and Havana, which are 

 the longest and most deeply submerged cables in use for telephonic 

 communication in the world. 



VIII. Extent of Commercial Application 



The following data will assist in visualizing the practical importance 

 of the developments which have been described in this paper. 



In 1911, when Mr. Gherardi addressed this Institute on the subject 

 of loading practise in this country, there w^ere about 125,000 loading 

 coils in service which loaded about 85,000 miles of open wire circuits 

 and 170,000 miles of cable circuits. Although precise figures are not 

 yet a\-ailable regarding the number of loading coils in service in the 

 Bell System as of January 1, 1926, conservative estimates set this total 

 at about 1,250,000 coils. These coils load about 1,600,000 miles of 

 cable circuits and 250,000 miles of open wire. In round numbers, 

 500,000 coils are installed on non-quadded local area trunk cables and 

 700,000 in toll and toll entrance cables (the bulk of these being quadded 

 cables). Nearly two-thirds of the total number of coils have com- 

 pressed iron powder cores, all of these being installed on cable circuits. 

 About 4500 coils having wooden cores are installed on carrier loaded 

 entrance cables. The remainder have iron wire cores, approximately- 

 60,000 being of the so-called "air-gap" types. 



Prior to the development of satisfactory types of telephone repeaters, 

 the principal use of loading coils was in exchange area trunk cables in 

 large metropolitan areas such as New York, Chicago, Philadelphia, and 

 Boston. The successful application of telephone repeaters to loaded 

 small gage cables has greatly increased the use of loading in the tele- 

 phone plant. As illustrating this trend, approximately 150,000 toll 



^''C. E. Krarup, Submirme Telephone Cables with In-reassd Sc'lf-Iiiduclion, 

 ETZ., 23:344, April 17, 1902. 



3^ W. H. Martin, G. A. AaJareg?. B. W. K-aliU, "K2/ VVi3t-4ivini S;i') narinj 

 Telephone Cable System," Trans. A. I. P:. E., Vol. 41, 1922, p. 184. 



