158 



THE ELECTRIC TELEGRAPH. 



94. Plan of Frischen and Siemens- Halske. About the same 

 date (1854) these celebrated engineers invented, independently 

 of each other, an improved system of telegraphing in opposite 

 directions in a single wire at the same time ; their plan, by 

 which the counteracting batteries and double keys both 

 sources of difficulty are entirely dispensed with, possesses 

 important advantages over the methods of Gintl, and brings 

 the problem of telegraphing in opposite directions as near 

 to perfection as is possible with the conditions of so delicate 

 an arrangement. 



Fig. 87 represents the plan of connections of two stations, 

 A and B. The negative pole of the battery E is connected to 

 earth, and the positive pole to the working contact of the 



Station A. Station S 



Jfcg. 87. 



ordinary transmitting key K; the back contact being, as 

 usual in the Morse plan, connected to earth. Instead of 

 the common arrangement of putting the relay in the earth 

 circuit from the back of the key, it is inserted above the 

 lever of the key. The relay consists of two coils, r and p t 

 of equal and opposite magnetic effects. The coil r is con- 

 nected between the lever of the key and line ; and the other 

 coil, p, between the lever and a resistance, R, to earth. 



When the resistance of r and p are equal to each other, 

 and R equal to the sum of the resistance in the circuit of the 

 line L L! and of one side, r lt of the relay at station B, &c., to 

 earth, then, on pressing down the key, the current of E 

 will be equally divided between the coils r and p, which 



