CONQUEST OF DISTANCE BY WIRE TELEPHONY 359 



cordingly, the imj:)roved insulation features of the experimental loaded line, 

 including the new porcelain insulator, were recommended^ for this use. 



The loading arrangements standardized for the 165 mil circuits were 

 similar to those which for several years had been standard for 104 mil 

 circuits, viz., 0.265 henry coils installed at intervals of about 8 miles. With 

 line insulation of 5 megohm-miles or better, the transmission range of the 

 loaded 165 mil circuits was about 2.3 times as great as that of non-loaded 

 165 mil circuits. 



Loaded Duplex Cable: 



The pioneering development work on duplex cable and on new types of 

 loading coils for the cable phantom and side circuits culminated in a com- 

 mercial installation between Boston and Neponset, which became ready for 

 service early in September 1910. 



By the fall of 1909, the experimental work and analysis of test data on 

 experimental lengths of cable having multiple-twin quads and spiral-four 

 quads respectively, and on the required new types of loading coils, had 

 progressed sufficiently to make it desirable to undertake trial manufacture, 

 preferably for a project that would meet a need for new facilities. In 

 November 1909, it was decided that the Boston-Neponset cable project 

 would be a suitable objective. About 5.8 miles of 37-quad 13-gauge cable 

 was required, extending south from Boston, partly for use as an entrance 

 cable for the American Company's Central and Shore (loaded open-wire) 

 lines, and partly as a suburban trunk cable for the New England Company. 

 The entrance facilities were to be provided with phantom group loading, in 

 anticipation of extensive phantom working on the open-wire lines. Since 

 phantom working was not needed or desired on the suburban trunks, the 

 loading for the New England Company was limited to the quadded pairs, 

 using side circuit type coils. This particular plan was more valuable from 

 the standpoint of development experience and gave greater plant flexibility 



^ Before the end of 1911, an appreciable degradation was noticed in the wet weather 

 Hne insulation of the initial installations. This appeared to be due to several causes which 

 could not be separately appraised, including (1) an unexpected retention of deposits on the 

 glazed surface, i.e. the insulator was not self-cleaning; (2) the nesting of insects underneath 

 the petticoats; and (3) trouble with a large number of defective insulators. In general, 

 the impaired insulation was not large enough to warrant the removal of the porcelain 

 insulators, except those that were physically defective, nor was the "bug trouble" suffi- 

 ciently serious to warrant the establishment of routine cleaning operations. Meanwhile, 

 the prices of the porcelain insulator increased drastically in consequence of the continued 

 manufacturing difficulties, which also greatly limited the supply of acceptable insulators. 

 About the middle of 1912 it was decided to start using double-petticoat glass insulators 

 on new installations of loaded 165 mil lines, in place of porcelain insulators. These glass 

 insulators had become available in consequence of development work undertaken late in 

 1910 for the Western Union Telegraph Co. (at that time closely affiliated with the Bell 

 System). The new glass insulators were much less expensive than the porcelain insulators 

 and their insulating properties were nearly as good. Subsequent experience showed them 

 to be fairly satisfactory for use on loaded 165 mil circuits. 



