HISTORY AND PROGRESS. 



135 



tacts. The lever is furnished with a spring, which presses 

 upon the contact a, by which, when the key is lifted up, 

 the contact with a is interrupted an appreciable time after 

 that with b. 



This is necessary, because if they were both interrupted 

 at the same instant it is evident that no induction current 

 could arise in the secondary coil, its circuit being broken. 



J 



\Eartl\ 



Fig. 74, 



By the contact a continuing an instant longer than b, how- 

 ever, the induction current which follows the interruption at 

 b has time to pass over a and through the line. 



The Morse telegraph has been worked by this system of 

 induction currents to- a considerable extent on the lines in 

 Eussia, Bavaria, and Hanover. Sibeller says that messages 

 have been sent direct, without translation, by this method, 

 on a line of 200 German miles, equal to nearly one thousand 

 English. 



Compared with the methods of working the Morse tele- 

 graph by voltaic electricity, that of induction currents offers 

 many advantages ; the line batteries are opened, and spaces 

 between the signals are given by reversed circuits, which 



