c. xxxv. EXPERIMENTS IN MAGNETISM. 347 



apart j exactly in the same way as magnets attract or repel 

 each other, according to the direction in which they lie. 



This may be difficult to understand without more expla- 

 nation, but you can remember that Ampere proved that elec- 

 tric currents produce magnetic currents at right angles to them- 

 selves in the air, without needing any bar of steel to help them. 



Electro-magnets made by means of an Electric Current. 

 It now occurred to Ampere that if electric currents give 

 rise to magnetic currents he ought to be able to magnetise a 

 steel bar by passing an electric current round it. So he 

 wound a copper wire (covered with silk to prevent the 

 electricity running into the iron) round a steel bar, and, 

 fastening the two ends of wire to a voltaic battery, he passed 

 a current through it (see Fig. 57). After a short time he took 



FIG. 57. 



Coil of Electrified Copper Wire turning a Steel Bar into a Magnet. 



the bar out and found it was a perfect bar magnet, which 

 would attract iron. The current of electricity, in passing 

 along, had magnetised the steel just as if it had been 

 rubbed on a loadstone. 



Steel is very close and hard, and when he used a steel 

 bar the magnetism remained after it was taken out of the 

 electric wire, but if he used a piece of ordinary soft iron the 

 magnetism passed away when the current ceased. He called 

 these magnetised bars electro-magnets, because they are made 

 by electricity. You can easily make them for yourself, and 

 you will find that an iron rod will hold up needles, nails, or 

 even keys as long as the current is passing, but they will all 

 fall off as soon as it stops, showing that it is the electric 

 Current which causes the iron to act as a magnet. 



