10 



C. Rapid Series of Induced Currents. Connect up an 

 induction coil with the screw terminals marked F, inserting 

 the wires into the binding-screws in the pillars at the end of 

 the primary coil, so as to bring the Neef 's hamnr into action 

 (fig. 3). Introduce a mercury key into the primary circuit 

 and a friction key into the secondary circuit as .before 

 (fig. 2). 



Eltctro- 



FIG. 3. End of Coil showing Neef* Hammer. 



Note that, when the mercury key is closed, the current passes 

 round* the electro-magnet, which pulls down the hammer 

 and spring, and thus breaks the contact at the screw in the 

 middle of the spring. The current is interrupted, the magnet 

 demagnetized and the spring bounds back. The number of 

 interruptions depends on the length of the spring. 



Open the friction key and pull the secondary coil well away 

 from the primary and apply the wires to the tongue. Close 

 the mercury key, and if no sensation is experienced push the 

 secondary coil nearer to the prftnary. Record the resulting 

 sensation. 



