81 



Fig. 15 

 Fig. 15 — a, b, binding posts of primary coil. 



Make and Break the P Circuit with the Key 1. Fig-. 16. 

 Do this smartly once or twice only and after each trial push 

 the S coil 1 centimeter towards the P coil. Let the co-worker 

 indicate when he feels the "shock" and whether he does so 

 at closure or opening. Note the position of the coil as soon as 

 the minimal break shock is felt ; it is perceived first. Proceed 

 with further trials until the make shock is also felt. Read off 

 the position of the S coil. It is considerably nearer to the P 

 coil. The break shock is the stronger of the two. Continue the 

 approximation of the S coil by short distances to the P coil. 

 The shocks will be stronger each time until finally unbearable. 



The strength of a stimulus can therefore be varied by 

 changing the relative position of the S coil. It may approxi- 

 mately be assumed to change inversely with the square of the 

 distance between the two coils. 



J3eMery, 



Fig. 16 

 Fig. 16. Apparatus as set up for make and break shocks. 



