HISTORY AND PROGRESS. 



103 



circular apparatus, 2, commutator, 3, L n , &c., and the 

 currents received or transmitted by the intermediate station, 

 L m , commutator, 4, back-contact of key, relay, 5, earth, &c. 



Fig. 54. 



In the second position, the circular- cur rent goes through 

 L 1 , 1, circular apparatus, 2, commutator, L m , &c., and the 

 station currents through L n , 3, commutator, 4, back-contact 

 of key, relay, 5, earth, &c. In the third position, circular 

 currents go over L n , 3, commutator,- 1, circular apparatus, 2, 

 commutator, L 111 , &c., and station- currents over L 1 , commu- 

 tator, 4, back-contact of key, relay, 5, earth, &c. 



The plan of connections for a station with four lines com- 

 bines both Borggreve's commutators ; and the combinations 

 in which the operator can arrange the lines are as follows : 



1. Li with Ln, and Lm with Lrv 



2. Li Lin Ln Lrv 



3. LII Lin Li Liv 



In each combination the positions of the lines with 

 regard to the apparatus may be : 



(1.) Direct, the station not receiving the message. 



