ELECTRO-MAGNETISM. 701 



the wire the iron bar is drawn completely within the 

 coils, the end b being now at d, the end a at c. When 

 the current is strong enough this motion takes place not 

 only when the glass rod is in a horizontal position, as 

 in the figure, but also when it is held vertical, so that 

 in that case the iron bar moves vertically upwards. 



This attraction between a current which traverses a 

 spirally coiled wire and a piece of iron lasts only as 

 long as the current traverses the spiral ; when the 

 current is stopped the bar of iron drops if the tube be 

 held vertical. 



The iron bar itself, while the current passes round it, 

 acquires properties similar to those which are manifested 

 by the spiral. It becomes likewise capable of attracting 

 iron. If a bar of iron smaller than the one in the 

 glass tube is placed in contact with the end which pro- 

 jects from the tube, as in fig. 354, it is attracted and 

 supported by it, and the small bar can support a second 

 one, and this perhaps a third. In this case 

 as in the former all manifestation of attrac- 

 tion ceases immediately on interrupting the 

 current; as soon as it ceases the bar in con- 

 tact with the one in the tube is released, the 

 other bars separate, and fall down in obedience 

 to the force of gravity. 



Phenomena of this kind are explained by 

 assuming that a closed electric current is 

 constantly passing round each individual FlG< 354 

 molecule of the iron, and that these infi- (rcal size} ' 

 nitely small currents (called Amperian currents after 

 the physicist who first proposed this explanation) have 

 under ordinary circumstances all possible directions; in 



