HISTORY AND PROGRESS. 131 



81. Morse Telegraph worked by Induction Currents. In 

 numerous instances has magneto- electricity been pressed into 

 the service of the telegraph, but always in conjunction with 

 the step-by-step or needle systems. For the Morse it was 

 considered useless, as the currents developed, being only of 

 momentary duration, are only capable of themselves of giving 

 successions of dots, whereas the Morse alphabet requires also 

 an elementary signal of longer duration. This difficulty was 

 removed by the ingenious invention of Siemens and Halske, 

 in the construction of a relay, the tongue or armature of 

 which would remain of itself on either contact, when once 

 deflected, until a current different from the one last sent 

 through removed it to the other side. If, therefore, when 

 the tongue was in a state of rest on the insulated contact, a 

 momentary current of magneto -electricity were sent in the 

 right direction through the coils of the relay, the armature 

 would move to the local contact, and would remain there, 

 closing the local circuit, notwithstanding the current which 

 deflected it had long since vanished, until a current in the 

 opposite direction brought it back to the reposing contact. 

 In this way either lines or dots could be produced at 

 pleasure by regulating the interval between the succeeding 

 currents. 



This principle is the same as that used at a later date in 

 the indicator of the magneto-electric telegraph of the same 

 inventors, which has already been described. 



The solution of this problem has placed at the command 

 of the telegraphist a source of electricity of much greater 

 intensity for working the Morse instruments through great 

 distances, than the voltaic current, and which he is able to 

 produce at a considerably less expense. 



The complete apparatus consists of : - 

 A transmitting key, 

 An induction apparatus, 

 A polarised relay, and 

 A Morse recording instrument worked by a local battery. 



The induction apparatus sometimes used consists of an iron 

 core a bundle of soft iron wires surrounded by convolu- 



K2 



