ELECTRICAL APPARATUS IN USE IN PHYSIOLOGICAL WORK 15 



circuit (Neef's hammer). This will be understood from the diagram 

 shown in fig. 23. The battery current is conveyed from the terminal, 

 t 3 , to a steel spring, sp, having a bar of soft iron at its free end, and 



t' t 2 



FIG. 22. INDUCTION COIL ARRANGED FOR SINGLE SHOCKS. 



the current passes from the spring, which has a plate of platinum 

 upon it, to the platinum point of a screw, s 1 , and thence through the 

 primary coil. Before passing back to the battery it is conducted 



FIG. 23. DIAGRAM OP DU Bois COIL ARRANGED FOR FARADISATION. 

 (FOR DESCRIPTION SEE TEST.) 



through a small electro-magnet, m ; the electro-magnet being thus 

 set in action, draws down the iron bar and with it the spring, which 

 leaves the screw and breaks contact so that a break induced current 

 is set up in the secondary coil. But, the current being broken, the 



