108 



PROCEEDINGS OF THE CANADIAN INSTITUTE. 



secondar\' coils being connected in circuit, the one in one branch of 

 the metallic circuit and the other in the other branch of the metallic 

 circuit. In the second method, repeating coils are used with one coil 

 in each branch of the metallic circuit, said coils being connected with 

 each other and also with an independent telephone circuit. 



- — '--p A 



B 



F 



Fig. 2. 

 In Fig. 2 A. and JS. are the two branches of a metallic circuit at one end of a telephone trunk 

 line. C. is a subscriber's line, and E. a receiving- telephone in said subscriber's line. D'. is a 

 transmitter with two induction coils at the central office. The secondarj- coil of coil a' is in 

 circuit with wire A, and the secondary coil of coil 6' is in circuit with wire B. M. is a micro- 

 phone, and L.B. the local battery connected with the primary coils of a' and b'. E. is the 

 differentially wound receiving telephone at the central office. 



In the tirst method the opei'ation is as follows : The voice impulse 

 vibrates the diaphragm of the transmitter, this varies the strength of 

 the local battery circuit traversing the primary coils of the two induc- 

 tion coils, this generates secondary currents in the two secondary coils 

 and this in turn generates electi'ical currents in the two branches of 

 the metallic circuit, and if the two coils are properly balanced, electrical 

 impulses are generated in each branch of the metallic circuit equally 

 and simultaneously, and if the connections are properly made, tliese 

 electrical impulses traverse the metallic circuit in opposite directions, 

 the currents generated in one coil being reinforced by the currents 



