MAGNETIC INDUCTION PRODUCED BY GALVANISM. 213 



the graphite end,\ and the blue towards the zinc 

 end. (If the direction of the spiral turns had been 

 opposite, the result wpuld have been opposite.) 



Now if we insert ^n this coil a bar of unmagnetized 

 steel, as in Figure Tip the bar is instantly magnetized, 



Fig. 71. 



and becomes a magnetic needle with its red pole to- 

 wards the graphite (the direction of the spiral being as 

 shewn in the figure) . This process is extensively used 

 for magnetizing compass-needles. 



If instead of the bar of steel we insert a bar of soft 

 iron (usually called the 'core'), the bar is magnetized 

 in the same manner as under other inductive force, 

 having its poles in the same position as those of the 

 steel bar just mentioned. But the magnetism is 

 transient, lasting only as long as the galvanic current 

 lasts. If the current be destroyed by interrupting the 

 circuit in any way, as by cutting the wire at any point, 

 or by separating two portions of the wire which are in 

 contact, or by separating the wire either from the zinc 

 plate or from the graphite plate, or by lifting either of 

 the plates out of the acid, in any of these cases, the 

 iron instantly loses its magnetism. And this property 



