RELAYS IX run nr.i.f. sysrr..\f 7 



and so on. Conse(iutMUl\'. a ri'la\ di-Nii^iUMl for one purpose ina\ ho 

 wliolly unfit for any other use. On this account, as the telephone 

 art has grown, new conditions and new requirements have resulted 

 in the development and manufacture of a large number of relays. 

 At first, this undoubtedly ft)llowed previously established precedents, 

 so that new forms were brought into existence which fulfilled im- 

 mwliate needs, but did not receive much consideration from the 

 standpoint of economy, standardization or consistency of design. 



At the present time, the Western Electric Company manufactures 

 for the Bell System about 100 types of simple electro-magnetic rela\s. 

 These types are subdi\ided into about 3,500 kinds, which differ in 

 minor ways, such as windings and contact arrangements. In 1021, 

 the Western Electric Company produced over 4,800,000 of these 

 relays. These figures serve to indicate the economic importance of 

 the relay in the present day system but do not giv^e any adecjuate 

 conception of the dependence of the communication network on 

 relays of all types. 



From a design standpoint it is possible, as has been pointed out, 

 to attain practically any desired result in an electric circuit, subject 

 of course to certain limitations as to time, and provided no limita- 

 tions as to economic application are to be met. The methods and 

 means for securing the desired operations involve the use of relays 

 of various types and designs, and may lead to new developments 

 which are obviously not economical. The relay may be called upon 

 to perform a single function, necessitating the opening or closing of 

 a single contact, or it may be required to efifect a complicated series 

 of transfers or circuit changes. Its operation may necessitate an 

 accurate synchronizing with other circuit operations involving a 

 time lag in its operation or release, and other requirements as to 

 impedance, power, etc., may be imposed. It frequently happens 

 that the conditions imposed by circuit requirements necessitate a 

 choice between new features of relay design and a complication of 

 the circuit to overcome limitations in existing types of relays. 



The economic considerations which gov^ern the final application 

 of circuits in the telephone system are, to a large extent, dependent 

 on the costs and performances of the various types of apparatus, 

 particularly the relays. Frequently, there may be a number of 

 possible methods of accomplishing a given result in an electric cir- 

 cuit and the most economical method is, of course, desired. This 

 does not necessarily indicate the least number of relays or the cheapest 

 but rather the most economical combination, taking into account 

 reliability of circuit operation and its el?ect on service, cost of equip- 



