HISTORY AND PROGRESS. 



99 



where a single apparatus only is used. The apparatus is put 

 in circuit between the screws 1 and 2, to which the lines L L 



L-2 



Fig. 52. 



and L 2 are respectively connected, while the earth-plate is 

 brought to one of the screws, 3 or 4. 



When the contact-cone is out, the current passes through 

 the apparatus in the circuit 



L 2> 2, A, 1, L!, 



that is to say, the intermediate station receives the signals 

 in common with a distant station. 



When the contact-cone is in hole in the apparatus is 

 short-circuited, and the current passes through 



L 2 , 2, contact-cone in in, 1, LI. 



When the contact-cone is in hole I the apparatus is used 

 as terminal of the line L 1? and the currents from LJ take their 

 way through L I? 1, A, 2, i, earth, &c. Those from L 2 through 

 i to earth. If the contact-cone is put in n the instrument 

 receives from and transmits to the line L 2 on the other side, 

 in the same way. In both positions the currents arriving 

 by the line which is not being corresponded with pass 



H 2 



