INDUCTION CURRENTS. 



261 



through the coils of wire that no motion was perceptible in the galvanometer. 

 But when the circuit was opened, and when it was closed, there was a slight 

 motion of the needle in the galvanometer, but in different directions. After 

 consideration the philosopher came to the conclusion " that a battery current 

 through one wire induced a similar current through the other, but for an 

 instant only." 



CErsted had already demonstrated that all magnetic effects were 

 attributable to the attraction and repulsion of electric currents ; and founding 

 his views upon the theory of Ampere, Faraday came to the conclusion that 

 electricity could be produced from magnetism, or that the electric current 

 could be obtained from magnets. This he succeeded in doing. By inserting 

 a steel magnet about half its length into a coil of wire, Faraday induced a 

 current to pass through the wire in two directions. Thus he proceeded to 

 solve all the mysteries of magneto-electricity, and stated that to produce 

 currents it was only necessary to " cut appropriately the lines of magnetic 

 force." 



The application of the magnet to the machines for electric lighting will be 

 shown further on. Very powerful currents are obtained by the induction coil ; 

 but the currents would not be of practical service were it not for the apparatus 

 called a Commutator, or key, which reverses the connection of the bobbins, 

 and turns the current at every half revolution. Just as if a current were being 

 sent across and back over a table, and when the current has reached the end, 

 an instantaneous wheel round, or pivoting of the table, sends tJie current on, in 

 continuation (but on the table all the time), because of the sudden change of 

 its position. The back rush being on the table, the movement of the latter 

 really makes the line continuous, and by quickly breaking and reversing the 

 -current in the commutator, the effect is gained in the machine. 



Electro-magnets and bobbin, etc. 

 (Clarke's machine) 



