82 



Remove the core of soft iron from the P coil. Find the 

 minimal shocks for break and make shocks and compare with 

 the readings in the previous experiments. 



Next take the S coil out of the slide and place it end on 

 and close up to the P coil. Whilst making and breaking the 

 P circuit turn the S coil so that its axis shall be ultimately 

 set at right angles to that of the P coil. The shocks v/ill 

 rapidly diminish and finally disappear as the position of the S 

 coil is changed. 



Explanation : When the battery current at closure of 

 circuit is rising in strength in the primary, an opposing induc- 

 tion current is thereby generated in the P coil itself, which 

 retards the battery current from attaining its full strength as 

 soon as it otherwise would, and of course the effect upon the 

 S coil is not so sudden a one. 



On breaking the P circuit an induction current is likewise 

 generated which has the same direction as the disappearing 

 battery current, and consequently it retards change of the 

 electrical condition but does not interfere much with the sud- 

 denness of the subsequent drop in potential and therefore the 

 effect upon the S coil is greater than at closure. 



313. Interrupted 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. 11. 



Fig. 17 



Fig. 17, C, binding post ; E, primary coil ; D, electro-magnet and binding 

 post. 



