BREAK EXTRA CURRENTS. 



191 



It is well, also, to bear in mind that contacts are by no means of negligible 

 duration, for they vary very much in different forms of instruments. This applies 

 also to ordinary keys. 



These are the salient features in the action of the Inductorium, but there are 

 others, such as the influence of the electromagnet of the interrupter, &c., which 

 cannot be considered here. 



Demonstration of the bpeak extra current as an illustration of 

 one of the induction effects in the P coil (Fig. 27). 



Remove the S coil from the Inductorium and set up as follows : 



First set up the Leclanche cell in circuit with the hand electrodes 

 with a "shorting" key (1). Hold the electrodes against your tongue, 

 and open and close the key nothing will be felt. The E.M.F. of 

 the current is not sufficient to produce 

 a stimulus through the resistance offered 

 by the skin. 



Now add to the battery circuit the 

 P coil (slip off the S coil and place 

 it on one side) with shorting key (2), 

 so that the P coil may be at will in- 

 or excluded from the circuit. 



Keep key (2) closed, and repeat the 

 trial as before, key (2) excludes the coil 

 from the circuit and the result is the 

 same (effect of "shorting"). Next open 

 key (2), then on opening key (1) a shock 

 is felt at break. This shock is due to 



the induction current which is generated in the coil by the fall of 

 potential in the battery circuit. The fall is due to the easier path 

 through key (1), being replaced by a path of greater resistance through 

 the tongue, and consequently a feebler current flows through the P 

 circuit, and this drop generates an induction current in the circuit, 

 and the latter having a higher E.M.F., is able to pass through the 

 tissues and to act as a stimulus. 



The effect is largely due to the iron core of the coil, for if the S coil be sub- 

 stituted the effect will not be so great in spite of the fact that this coil presents in 

 the larger number of its turns of wire, a condition favourable to the production of 

 more powerful induction effects. 



Interrupter shocks. Detach the wires from A and B and transfer 

 them to the binding screws C and D. Adjust the top contact screw E 

 so that it touches the spring lightly (Fig. 26b). 



On closing the P circuit this spring oscillates, automatically opening 

 and closing the P circuit, and a succession of induction currents are 

 generated in the S coil. 



FlG. 27. Break extra current. 



