THE BREAK EXTRA-CURRENT OF FARADAY. 143 



instantaneously a shock is felt as before ; this is the opening 

 or break induction shock. 



(c?.) Observe that the break is stronger than the make shock. 

 Push the secondary coil a long distance from the primary, 

 and with the electrodes on the tongue, make and break the 

 primary circuit, and gradually move the secondary near the 

 primary coil. Observe that the break shock is felt first, 

 and on pushing the secondary nearer the primary coil both 

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

 shock. 



2. Interrupted Current by using Neef's Hammer Apparatus. 

 The same as for single shocks. 



(a.) Connect the battery wires as in Fig. 46, i.e., to the 

 binding screws in the erect pillars, P' ( + ) and P" ( - ). In- 

 troduce a du Bois key as for the make and break arrange- 

 ment. The automatic vibrating spring, or Neef's hammer, 

 is now included in the primary circuit. Set the spring 

 vibrating. Make the current by depressing the handle of 

 the key. The elastic 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 elastic 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. 



(b.) While Neef's hammer is vibrating, apply the electrodes 

 to the tongue or finger as before, noting the effect produced 

 and how it varies on altering the distance between the 

 secondary and primary spirals. 



3. The Break Extra- Current of Faraday. When a galvanic 

 current traversing the primary coil of an induction machine is 

 made or broken, each turn of the wire exerts an inductive in- 

 fluence on the others. When the current is made, the direction 

 of the extra current is against that of the battery current, but at 

 break it is in the same direction as the battery current. Appara- 

 tus. Daniell's cell, two du Bois keys, five wires, induction coil, 

 ordinary electrodes (and nerve muscle preparation). 



(a.) Arrange the apparatus according to the scheme 



