358 



ELEMENTARY LESSONS ON [CHAP. x. 



146), a momentary current is observed to flow round 

 the circuit while the magnet is being moved into the 

 coil. So long as the magnet lies motionless in the coil 

 it induces no currents. But if it be rapidly pulled out of 

 the coil another momentary 

 current will be observed to 

 flow, and in the opposite direc- 

 tion to the former. The in- 

 duced current caused by in- 

 serting the magnet is an 

 inverse current, or is in the 

 opposite direction to that 

 which would magnetise the 

 magnet with its existing polar- 

 ity. The induced current 

 caused by withdrawing the 

 magnet is a direct current. 



Precisely the same effect is 

 produced if the coil be moved 

 towards the magnet as if the 

 magnet were moved toward 

 the coil. The more rapid the motion is, the stronger 

 are the induced currents. 



393. Induction Currents produced by Cur- 

 rents. Faraday also showed that the approach or 

 recession of a current might induce a current in a closed 

 circuit near it. This may be conveniently shown as an 

 experiment by the apparatus of Fig. 147. 



A coil is joined up to a sensitive galvanometer as 

 before. A smaller coil of stout wire is connected to the 

 poles of a battery (a single Bunsen's cell in Fig. 147), so 

 as to be traversed by a current. On approaching or 

 inserting the smaller or "primary " coil into the larger 

 or " secondary " coil, a momentary inverse current is 

 produced ; and on removing it a momentary direct 

 current (*>., one which runs the same way round the 

 outer secondary coil as the primary current which 



Fig. 146. 



