500 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1915. 



During the last few years thoroughly reliable mechanisms have 

 been produced for selectiA-ely signaling a large number of telephone 

 stations on the same line. With this mechanism the dispatcher, by the 

 simple process of turning a particular key at the central point, oper- 

 ates a signal, usually a bell, at the desired station without signaling 

 any of the other stations on the line. As soon as the called operator 

 picks up his telephone he, and he alone, is in direct communication 

 with the dispatcher over a high-grade telephone circuit. 



The development of this effective signaling apparatus has removed 

 the principal obstacle to the general adoption of the more effective 

 and flexible telephone and it seems only a question of time when 

 practically all train dispatching will be done by this means rather 

 than by telegraph. 



TELEPHONE APPARATUS. 



Because of the rapid development of the telephone art it has actu- 

 ally been difficult, at times, to produce the new apparatus needed to 

 keep pace with the service requirements. This was particularly true 

 in the period preceding 1905. The result was that 10 years ago the 

 telephone system was employing a great variety of apparatus per- 

 forming almost identical functions and consequently the quantity of 

 each special type of apparatus required was small and the manu- 

 facturing costs correspondingly high. 



With the telephone industry assuming gigantic proportions this 

 state of affairs obviously could not continue indefinitely without 

 entailing great monetary waste. About eight years ago, therefore, 

 the matter of unifying telephone apparatus as much as possible was 

 undertaken with the result that there are to-day lines of apparatus 

 with but slight differences in structure which are capable of per- 

 forming a varietj'' of functions. This has been brought about largely 

 by the employment of unit types of constructions capable of being 

 assembled in a variety of ways. 



All this has resulted in the adoption of more effective methods of 

 manufacture with a consequent reduction in cost. One of the most 

 noteworthy results of this general development has been the substi- 

 tution of parts punched and formed from sheet metal for parts 

 previously made from castings or machined from solid stock. This 

 use of sheet metal has also resulted in lighter and simpler apparatus, 

 occupying less sj^ace in the switchboard or substation. 



A noteworthy example of this standardization of types is found 

 in relays, of which hundreds of thousands are employed in central 

 office equipments. A few years ago there were almost as many types 

 of relays as there were individual service requirements. To-day this 

 has been changed and the number of types reduced to very small 

 proportions — ^the necessary service requij-ements being obtained by 



