44§ ENGINEERING ON THE FARM 



are not used, batteries are not associated with each tele- 

 phone, the transmitter and the primary of the induction 

 coil are connected in the line, the receiver and the in- 

 duction coil secondary form a local circuit, and, usually, 

 a device known as a condenser is placed in series with the 

 bell. The condenser is used for preventing a continuous 

 flow of direct current from the central office through the 

 windings of the bells, which, in addition to being wasteful, 

 would complicate the operation of the central-office signals. 

 The condenser also aids in augmenting or boosting the voice 

 currents by increasing the range of voltage variation. 



The particular system of exchange or switchboard service 

 referred to herein is what is known as the manual type. 

 Other systems are known as intercommunicating, semi- 

 mechanical, and mechanical or automatic. The intercom- 

 municating and automatic systems involve other switching 

 apparatus in addition to that described as a part of the 

 telephone instrument. 



Rural lines. If it is desired to provide telephone service 

 for a user or for a group of users in any locality, it is desirable 

 first to ascertain what facilities have been established by the 

 telephone company or companies operating in the locality 

 for caring for the needs of the people in the neighborhood. 

 If the prospective users are in or near the corporate limits 

 of a city or village having exchange service, it will usually 

 be best to obtain telephone service from an established tele- 

 phone company offering service to patrons on a rental basis. 

 If the prospective users are on or near an established toll 

 line or interurban route of an established company, it may 

 be found that, all things considered, the telephone company 

 can provide the desired service more economically than can 

 an individual user or a group of users acting for themselves. 

 If it is found that the construction of a line offers the most 

 satisfactory means of obtaining telephone service, the mat- 

 ter of making arrangements with the telephone company or 

 companies for exchange and toll-line service should receive 



