102 THE ELECTRIC TELEGRAPH. 



may be passing through the line in either direction. Suppose 

 the peg to be inserted in the hole 3. The currents coming 

 from the direction L I? go then from L X through' G 1 , peg 3 of 

 the commutator c 2 , coils of relay on the right, back contact 

 of K 2 , lever K 2 , commutator u, G 2 , L 2 , &c. The relay 

 R 2 will be set in action and work the Morse M 2 , which will 

 print all the signals passing from the line L 1 into the line 

 L 2 . 



69. Commutator for Stations with three or four lines from 

 different directions. Where more than two lines from differ- 

 ent directions meet at a station, it is required to employ a 

 commutator by which, whilst one or two lines are being 

 corresponded with, the remainder can be connected up, two 

 and two, for circular correspondence. 



When three lines meet at a station a commutator, arranged 

 by Borggreve, is usually employed, by which any two of the 

 lines may be connected together in circuit with a galvano- 

 scope, or complete recording apparatus, while the third line 

 is open for telegraphic communication from the same station 

 as terminal. 



When four lines meet, it is necessary to arrange the com- 

 mutator so that, upon occasion, they may be connected up 

 two and two with intervening receiving apparatus, by which 

 the corresponding stations are in direct communication, and 

 the intermediate stations able, at the same time, to participate 

 in the information transmitted. 



Fig 54, a, gives a plan of connections of Borggreve's com- 

 mutator for three lines, by which the following combinations 

 are possible : 



1. L 1 circular with L 11 , L m with apparatus. 



2. L 1 L m , L n 



3T n T in T i 



-L* j> -L* > -L* )> )> 



In using this commutator three of the holes are always 

 stoppered at the same time. Fig. 54, 5, gives the position 

 of the stoppers in the holes answering to the positions 1, 2, 

 and 3, above. 



In the first position the circular current traverses L 1 , 1, 



