EXPERIMENTS ILLUSTRATING THE USE OF APPARATUS IQ 



electrodes on the tongue. Make and break the cell circuit by 

 closing and opening the key k l . If this is done when the primary 

 coil is included in the circuit (i.e., with k 2 open as in the diagram) 

 the stimulus is sharp owing to the "extra" currents, but if the coil is 



FIG. 25. Experiment for showing effect of extra current. 



shunted out by closing k 2 the stimulus is hardly perceptible to the 

 tongue. 



6. Instead of placing the simple key in the primary circuit (as in 

 Fig. 22) place it in a side circuit (Fig* 26). On closing and opening the 

 key, shocks are still produced in the secondary circuit, although the 

 current through the primary coil is not made and broken, but only 

 altered in strength. The make and break shocks in the secondary 



FIG. 26. Diagram of experiment to show the effect of closing and opening a 

 side circuit to primary coil, fc, key in side circuit ; k l , key in secondary 

 circuit. 



coil are now more uniform, but are both weaker. This is the same 

 effect as is obtained for rapidly interrupted shocks by the use of the 

 Helmholtz wire (see p. 17). 



7. Take the secondary coil out and place it across the direction of 

 the primary coil instead of in its usual position. The making and 

 breaking of the primary circuit now produce no effect on the secondary 

 circuit, but induced currents begin to show themselves if the secondary 



