MAGXETO-ELECTRIC CURRENTS. 



bobbin. An electric current will then be transmitted on the wire 

 m o , the presence of which may be rendered manifest by a 

 galvanometer. This current, however, will be only momentary, 

 being manifested only at the moment the pole of the magnet 



Fig. 61. 



enters the core of 

 the bobbin. It 

 ceases immedi- 

 ately after that 

 entrance. 



Xow if the 

 magnetic bar 

 after entering be 

 as suddenly 



withdrawn, another current will be 

 produced upon the wire m o n, which 

 will also be only momentary, but its 

 direction on the wire will be con- 

 trary to that produced by the en- 

 trance of the magnetic pole. 



Thus if upon the entrance of the 

 pole jr a current is produced, running 

 in the direction m o n, the with- 

 drawal of the pole x will produce a 

 current running from n o m. 



If the south pole s be passed into 

 the core and withdrawn, momentary 

 currents will in like manner be pro- 

 duced, but they will have contrary 

 directions. 



If the wire m o terminated at o, 

 no matter what may be the distance 

 of o from m, were put at o in me- 

 tallic communication with the earth, 

 or with a plate or other mass of 

 metal buried in the earth, and if the 

 extremity n of the wire of the coil 

 were put in metallic connection with 

 the earth in the same manner at n, 

 the transmission of the instantaneous 

 .currents would take place exactly in 

 the same manner as above described, 

 because in that case the earth would 

 play the part of a conductor between the end of the wire m o at o, 

 and the end of the coil wire n. 



But if the metallic continuity either of the wire m o n, in case it 



207 



