MAGNETISM AND ELECTRICITY 209 



opposite directions. But let copper strip face zinc strip and the 

 corks tend to float apart. 



Ampere perceived from these experiments that there must 

 be some intimate relation between magnetism and electricity, 

 and he wondered if it might not be possible to make a bar of 

 steel into a magnet by using electric currents. He tried various 

 ways of doing this and finally hit upon this plan. He wound 

 about a steel bar many turns of copper wire, covered with silk 

 so that the electricity would not escape into the iron, and let a 

 current of electricity run through the wire for some time. When 

 he . removed the windings from the steel bar, he found it was a 

 magnet. This experiment is worth repeating. Wind a fairly 

 coarse insulated copper wire about a bolt or nail, making many 

 turns, and connect the ends of the wire with the binding-posts of a 

 dry battery. You will find now without removing it from the wind- 

 ings that it is a magnet an electromagnet, since it is made by elec- 

 tricity. Such a soft iron core does not remain a magnet when the 

 current is turned off; it is a temporary magnet. It was later 

 discovered, as we have shown above, that a coil of wire behaves 

 as a magnet when a current is running through it. Its magnetic 

 property is strengthened if the coil is wound about a core of soft 

 iron. 



An explanation somewhat as follows will serve to give a mental 

 picture of what probably goes on in the iron bar when it is changed 

 to a magnet. Conceive that the molecules of the iron are each 

 a tiny magnet. They do not lie, in the unmagnetized bar, with 

 their like poles pointing in the same direction but rather in any 

 and all directions. They do not pull together, therefore, but at 

 cross-purposes and so neutralize each other. When, however, the 

 electric current flows in the wire wo;und about the iron bar, it 

 causes the molecules to assume a position in which like poles all 

 point toward the same end of the bar, when it becomes a magnet. 

 In a soft iron bar the molecules resume their varying positions 

 when the current ceases; but in a steel bar, which has greater 

 rigidity since the molecules do not move readily, they remain 



