172 PRACTICAL PHYSIOLOGY. [XXVIIL 



coil both shocks are felt, but the break is stronger than the make 

 shock. 



Note that : — 



(i.) The break shock is the stronger. 



(ii.) On approximating the secondary to the primary coil, a 

 shock is felt at make also, t.e., when the primary 

 circuit is made, 

 (iii.) If the primary circuit be kept closed, i.e., made, no 



shock is felt. 

 (iv.) The shocks increase in intensity the nearer the 

 secondary coil is to the primary 

 N.B. — Make a table of the results showing the distance of the 

 secondary coil from the primary when testing the relative effects 

 of M. and B. shocks. 



Single M, and B. Induction Shocks (i Daniell). 



Distance of Secondary Coil Effect on Tongue, 



from Primary in cm. M. B. 



19 o o 



ig O Slight shock. 



17 O Stronger shock. 



9 Slight shock. Maximum shock, 



8 Stronger shock. ,, ,, 



7 Maximum shock, ,, ,, 



(«.) Remove the secondary spiral from its slot, and place it in line with 

 and about 15 cm. fiom the primary. Rotate the secondary coil so as to place 

 it at variable angles with the primary. Make and break the primary circuit, 

 and test how the strength of the induced current varies with the extent of 

 rotation of the secondary spiral. 



2. Interrupted Cunent, i.e., Repeated Shocks, by using Neef s 

 Hammer — {Alternating CuiTents) — Faradisation. 



{'(.) Connect the battery -svires (fig. 100) to P' ( + ) and P"( - ). 

 Introduce a Du Bois key as for the make and break arrangement. 

 The automatic vibrating si)ring, or Keef's hammer, is now included 

 in the primary circuit. Set the spring vibrating. 'Close the 

 key in the primary circuit. The spring, H, is attracted by the 

 temporary magnet, B', thus breaking the contact between the 

 spring, H, and the screw, S', and causing a break shock in 

 the secondary coil. B' is instantly demagnetised, the spring 

 recoils and makes connection with S', and causes a make shock. 

 Thus a series of make and break induction shocks following each 

 other with great rapidity is obtained, but the make and break 

 shocks are in alternately opposite directions. 



