fiff.'t. 



^uf.5. 



Figure 8o. — Patent drawing of Carty's use of the "phantom" 

 circuit for a combination telegraph and telephone line (''fig. 4") 

 and for a system of telephones ("fig. 5")- From U.S. patent 

 348512 (August 31. 1886). 



York with Boston and Philadelphia by the niiddle 

 of the 1880's and New York with Chicago by 1892. 

 Some attempts were made to treat telephone 

 lines as telegraph circuits and to duplex them.*^ 

 In 1883 F. Jacob made an unsuccessful attempt to 

 set up a bridge circuit for telephone lines, using 

 resistances only.^* One of the first steps toward 

 the development of a practical bridge circuit was 

 J. J. Carty's invention of the "phantom" circuit 

 (fig. 80) in 1886. Carty's circuit used induction 

 coils instead of resistances, and it enabled three 

 telephone conversations to be carried on over two 

 pairs of wires. However, this system was difficult 



63 Ibid., pp. 189-195. 



64 F. Jacob, U.S. patent 2872S 



(October 23, 1883). 



to apply and so did not come into even limited 

 commercial use until the winter of 1902-1903. 



During the 1890's there were many steps — some 

 of which were taken without any understanding of 

 electricity, and some on a sound basis — toward a 

 wireless telegraphy and wireless telephony, but, 

 practically speaking, there were no commercial 

 wireless systems in operation before 1900. 



Those electrical communications systems that 

 began as unwanted "philosophical toys" eventually 

 became essential ingredients of 19th-century society 

 in war and peace, in urban growth and national 

 expansion, in stimulating the economic ties between 

 nations, and in the corporate growth within nations. 

 But these important developments are beyond the 

 scope of this article, in which we have sought only 

 to trace the invention and application of the new 

 instruments in terms of the technology of the period. 



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