THE INDUCTION COIL. 753 



magnetic ; the piece of iron e is attracted by it, the contact 

 between / and the point of s ceases, the circuit is opened, 

 and the bundle again loses its magnetism. The piece e is 

 then brought back to its former position by the spring /, 

 the circuit is again closed, the bundle becomes magnetic, 

 and this action is repeated in rapid succession, as long 

 as K\ and K 2 are connected with the battery. The rapid 

 motion to and fro of / and e causes a buzzing sound ; 

 arid if the primary current is sufficiently intense small 

 sparks are seen at the point where contact is broken. 

 Induced currents, alternately in opposite directions, are 

 produced in the secondary coil at each making and 

 breaking of contact. 



Induced currents are of very short duration, but 

 possess considerable tension, and traverse inferior con- 

 ductors far more easily than the primary currents pro- 

 duced by the battery itself. Their effects upon the 

 human body are very powerful. If two copper wires 

 with handles of metal be clamped in the binding-screws 

 &! and & 2 , arid the handles are held in the hands, a suc- 

 cession of shocks will be felt, due to the continuous 

 renewal of the induced current. 



One Meidinger element is capable of setting the apparatus, fig. 378, 

 in activity and of producing sensible effects. In using so weak an 

 element the screw s must be accurately adjusted, that the point may 

 touch the spring as gently as possible. Before seizing the handles 

 the hands should be slightly moistened, in order to increase the con- 

 ductivity of the skin. When the coil is worked with a Grove or 

 Bunsen cell the effect is very sensible, even if the hands are dry. 

 Persons who are rather sensitive to electric shocks should fill the 

 cell only to about one-fourth with acid, or the sensation may be 

 unpleasantly strong. Strong currents produce spasmodic contrac- 

 tions of the muscles, and a powerful effort is often required to open 

 the hands and release the handles. 



The handles are made of two rectangular pieces of sheet zinc or 



3c 



