APPARATUS 



examine the connections; diagrams of these are given 

 in Fig. 2. 



3. The galvanic current. Connect one pole of the 

 cell by an insulated copper wire with one binding screw 

 of the in-circuit key (Fig. 2 a) and the electrode wires 



J.--Q 



O 



a 



Fig. 2. 



Fig. 2 a. Diagram of switch for use as an in-circuit key; 1 and 2 are 

 the binding screws. For use as a short-circuit key, the two single 

 binding screws are replaced by two pairs (1, I' and 2, 2' of Fig. 2 6), 

 each pair being connected by a brass plate. Note that when the 

 knob K is pushed towards the binding screws the key is open 

 (i.e. current cannot pass through it), and that when the knob is 

 pushed away from the binding screws the key is closed. 



with the other pole of the cell, and with the other bind- 

 ing screw respectively. Place the electrodes firmly on 

 the lip or tongue, close the key and in a few seconds 

 open it. Little or nothing will be felt, since the current 

 is not of sufficient strength. 



On a side table are three cells joined in series. Repeat 



