254 



VOLTAIC ELECTRICITY. 



copper wire, also silk covered. The two ends of this wire, 

 which constitute the secondary coil, are seen connecting 

 with the galvanometer O. Wires from the two plates of 

 a Voltaic element dip into mercury in the cups gg' 9 thus 

 closing an inducing circuit through the primary coil. 

 While this circuit is closed, the galvanometer is at rest, 

 showing that no current is passing through the secondary 

 coil. By lifting one of the wires from one of the cups, 

 the inducing current is interrupted. At this instant the 

 galvanometer needle is deflected as by a sudden impulse, 



FIG. 199. 



which immediately passes away. This shows the existence 

 of an instantaneous induced current in the secondary coil. 

 The direction in which the needle was turned, shows that 

 the secondary current was direct, i. e.,that it had the same 

 direction as the inducing current. If the wire just removed 

 from the cup be replaced and the inducing current thus 

 re-established, the galvanometer needle will be momenta- 

 rily turned in the direction opposite to that in which it 

 was previously turned. These experiments lead to this 

 conclusion : ~\^en a current begins to flow through 

 the primary coil, it induces an inverse current in 

 the secondary coil; when it ceases to flow through 



