might be found to increase the inductance artificially. This sugges- 

 tion was taken up by two investigators in America, Professor M. I. 

 Pupin of Columbia and Dr. G. A. Campbell of the Bell System who, 

 working independently, proved by further mathematical development 

 that this could be done practically and showed how to do it. These 

 mathematical studies showed that, while the addition of inductance in 

 large quantities at one or several points in the circuit destroyed its 

 capability for transmitting telephone currents, the insertion of induc- 

 tance in smaller quantities at regular and frequent intervals by means 

 of highly efficient inductance coils would greatly improve the trans- 

 mission efficiency. 



hiterurban Toll Cables 



The development of practical means of applying the loading principle 

 had been stimulated by the need for some practical means of improving 

 the efficiency of toll cables. This principle led promptly to the ex- 

 tension of interurban toll cables, important items being the installation 

 in 1906 of cables between New York and Philadelphia, a distance of 

 about 90 miles, and between New York and New Haven, a distance 

 of about 80 miles, and, in 1908, of a cable between Chicago and 

 Milwaukee having a length of about 90 miles. At about this time 

 experimental work was being actively conducted by the Bell System 

 in the effort to develop a type of construction for toll cables which 

 would perrpit the use of phantom circuits in the cables as well as in 

 open wire. This required a new technique in cable construction, 

 involving new principles and many refinements in detail to eliminate 

 the interference which would exist between phantom circuits and the 

 side circuits from which the phantoms are derived and also between 

 phantom circuits in the same cable. The processes worked out in- 

 cluded not only manufacturing methods but new types of electrical 

 tests and new splicing procedures applied in the course of installation 

 by means of which the unbalances in successive lengths of cable are 

 made to largely neutralize each other. As a result of this work, a 

 successful phantom cable was installed between Boston and Neponset, 

 Massachusetts in 1910, a distance of six miles. 



This work led to the inauguration in 1911 of a very important 

 interurban cable project. At the time of the inauguration of President 

 Taft on March 4, 1909, a sleet storm of unprecedented severity had 

 broken down all the wire lines entering W'ashington and isolated the 

 Capitol from the rest of the country. The Bell System management 

 determined that, as soon as technical advances made it possible, means 

 would be adopted for insuring against any future similar interruption 



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