154 



THE ELECTRIC TELEGRAPH. 



thereby put in motion, interrupts the current of Line I. between 

 the screw F, and spring D ; and, by the separation of the 

 beam of M' from the upper contact H, divides the local circuit 

 of M, which, therefore ; in spite of the movement of its relay, 

 remains passive. 



91. Methods of Telegraphing in Opposite Directions at the 

 same time in a ftingle Wire. This feat was for a long time 

 considered to be an impossible one. Judging from the plans 

 employed for ordinary circuits, it was urged that on sending 

 currents of equal intensity in opposite directions from the 

 ends of a single wire, they would eliminate each other, and 

 no indications, could be observed at the relay or other receiving 

 apparatus. 



92. The 'problem was first solved in the year 1853 by 

 Dr. Gintl,* an Austrian telegraph director, a plan of whose 



Fig. 85. 



arrangement is shown in Fig. 85. The conditions which it 

 was necessary to observe were, that the relay or other 

 receiving instrument at each of the stations should remain 

 always in circuit with the line, and that the currents trans- 

 mitted from either station should nevertheless not affect the 

 relay of that station. 



These two conditions are fulfilled by Gintl's plan by the 

 * Schellen, p. 310. 



