DEVELOPMENTS IN TELEPHONY AND TELEGEAPHY JEWETT. 499 



The most notable results have been obtained in connection with the 

 operation of telephone and telegraph lines in proximity to single- 

 phase alternating-current railways. In this type of power transmis- 

 sion circuit tlie inductive eiFects may be felt at distances measured 

 by miles rather than by feet, while on wires in close proximity to the 

 railway line the induced potentials may at times reach hundreds or 

 even thousands of volts. The problem of protecting low-voltage cir- 

 cuits against these excessive potentials led to the development of 

 what are known as compensating transformers, which, although caus- 

 ing some transmission loss when introduced into the telephone cir- 

 cuit, serve effectively to limit the voltage rise in the circuit to a point 

 which endangers neither the operation of the circuit nor the lives of 

 those employing it. 



In connection with high-tension interference, it is interesting to 

 note that in the United States the difficulties from interference which 

 beset the telephone and telegi'aph engineer have reacted to produce 

 material alterations in the methods of power circuit operation origi- 

 nally proposed. Further, there is to-day a concerted desire on the 

 part of telephone, telegraph, and power engineers to introduce 

 methods of operation which will be productive of minimum incon- 

 Aenience to all concerned. 



The great growth in th« high-tension network which covers the 

 country, particularly in the thickly settled commercial sections, has 

 added hazards to life and property as well as inductive disturbance 

 troubles to the problem of the telephone and telegraph engineer. 

 With the increasing complexity of the aerial line plant and more 

 particularly through the economic and legislative necessity for 

 reducing the number of pole lines to a minimum by joint occupancy 

 of low and high-tension wires, the possibility of physical contact, 

 particularly in times of storm, has been greatly enhanced. One of 

 the very great advances which has been made in the last few years 

 has been in defining proper specifications for joint use construction, 

 proper specifications for safe construction at crossing points of low 

 and high-tension wires, and the formulation and adoption of proper 

 types of pole-line construction for low and high-tension wires in 

 general. 



TELEPHONES FOR TRAIN DISPATCHING. 



In the railroad field the use of the telegraph for controlling train 

 operations is rapidly giving way to the telephone. Up to a few years 

 ago the telegraph offered the only feasible means for handling this 

 class of service, which required the dispatcher, located at a central 

 point, to keep in constant touch with a large number of stations along 

 the line. There were frequently as many as 50 or 60 of these stations, 

 and each office had a predetermined call or code which enabled the 

 dispatcher to call in the particular operator wanted. 



