France 



153 



the system in the l Annales Telegraphiques ' prior to the date of 

 Mr. Jacob's patent. The arrangement used in France is shown 

 in fig. 38, in which s 1 s 2 respectively represent the telephone and 

 telegraph stations. At s 1 , K is a calling key, v a calling battery, 

 j 1 j 2 jacks for the loop and single line switching, and T a translator. 

 At s 2 , R is a double-wound bobbin of small resistance and high 

 self-induction, in derivation with the two wires of the metallic 

 circuit trunk line, and connected so that currents passing through 

 the equally-wound coils oppose and kill each other. The other 

 terminals are joined to the telegraph instrument i and the 

 .adjustable condenser c. M. Cailho, whose plan, it will be seen, 

 differs only from Mr. Jacob's in the character and connection of 

 the resistances, states that the thick wire and opposite winding 



r- 



FIG. 39 



allow the telegraphic currents to pass uninfluenced by resistance 

 and self-induction, while the bobbin acts as a choke coil for the 

 telephonic currents. The calling battery v may be too weak to 

 operate the indicator at the distant end directly, as it is found that 

 the return or extra current from the double-wound bobbin at the 

 further station which follows the lifting of the key K, is always 

 strong enough to actuate the drop. 



M. Picard's plan depends on the use of a differential trans- 

 lator as indicated in fig. 39, which is a plan of the connections 

 used at the Rue Gutenberg. The currents arriving from the tele- 

 graph office split between the equal branches of the translator 

 secondary TS and produce no effect on the primary TP ; they also 

 neglect the double-wound indicator i. The calling is done hy 

 inserting a battery plug in the jack j 1 , while subscribers are con- 



