SCIENCE IN THE INDUSTRIAL WORLD 



to meet the increasing demands of the rapidly growing 

 telephone systems. In the early days of telephones, 

 when there were but few subscribers, but more than 

 one operator could take care of, the calls were trans- 

 ferred from one operator to another by what was 

 known as a transfer. Later, the multiple switchboard 

 was devised, thus eliminating the transfer. Now the 

 still greater increase in number of telephones has car- 

 ried the capacity beyond that of the multiple switch- 

 board, thus making necessary the establishment of 

 branch exchanges with trunk connections." 



The growth of the telephone has been such that in 

 the larger cities a great many exchanges have been 

 found necessary. In the five boroughs of New York 

 city, for example, there are at the present moment 

 (1910) fifty-seven exchanges in operation, and new ones 

 are constantly being established. It is obvious, there- 

 fore, that under these conditions, the multiple switch- 

 board is no longer the most economical form of 

 equipment, since the large majority of a subscriber's 

 calls will probably be for a station other than his 

 own. 



Hence in large cities it has become the practice to 

 do away with the subscriber's multiple switchboard 

 at his own exchange, and treat every call as a "trunked" 

 call. This method has proved expensive both in first 

 cost and operation, and out of it a system, technically 

 known as the "semi-automatic," has been developed, 

 which eliminates a considerable number of the operators 

 necessary in the manual system, and does not require 

 the intricate mechanism of the automatic. It can be 



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