VOLTAIC ELECTRICITY. 



255 



the primary coil, it induces a direct current in the 

 secondary coil; both induced currents are merely 

 instantaneous. 



4O5. Currents Induced by Change of Dis- 

 tance. If the primary coil be made movable, as shown 

 in Fig. 200, and, with a current passing through it, be 

 suddenly placed within the secondary coil, the galvanom- 

 eter will show that an inverse current was induced in the 

 outer coil. When the needle has come to rest, let the 

 primary coil be removed, and the galvanometer will show 

 that a direct current was induced. 

 From this we see that when the 

 primary coil, bearing a cur- 

 rent, is brought near the sec- 

 ondary coil, a momentary 

 inverse current is induced in 

 the latter; that ivhen the 

 coils are separated, a direct 

 current is induced. 



4O6. Magneto -electric 

 Induction. If, instead of the 

 primary coil bearing the inducing 



current, a bar magnet be used, as 

 FIG. 200. ghown in Fig> 2Q1 ^ the results 



produced will be like those stated in the last paragraph. 

 Wlien the magnet is thrust into the interior of the 

 coil, an induced current will flow while the motion 

 of the magnet continues. ]Vhen the magnet is 

 stationary the current ceases to flow, and the needle 

 gradually comes to rest. When the magnet is with- 

 drawn, an induced current flows in the opposite 

 direction. 



