216 



Our Surroundings 



observe the effect of the electric current on the needle. It will 



indicate the direction of the magnetic lines of force. 



In 1831 two scientists, 

 Joseph Henry, an American, 

 and Michael Faraday, an 

 Englishman, working sepa- 

 rately, discovered that when a 

 magnet is moved inside of a 

 coil of wire a current of elec- 

 tricity is started in the wire. 

 This led to the development 

 of machines to generate elec- 

 tricity, in which magnets were 

 made to move within coils of 

 wire or coils of wire to move 

 within magnets. This was 

 the beginning of the modern 

 dynamo. 



The Electromagnet. 



The material part of an electromagnet is merely a piece of 



soft iron encircled by a coil of insulated wire. One can be made 



by placing an iron nail within a coil of insulated wire. Such a 



device, however, does not act 



as a magnet until a current of 



electricity is flowing through 



the coil. The coil is called a 



helix. When energized by an 



electric current, the nail gains 



the properties of a bar mag- 

 net; that is, it has a north 



magnetic pole at one end and 



a south magnetic pole at the 



other end. This may readily 



be shown by testing with a 



magnetic needle. 



An electromagnet is an essential part of almost all electrical 



machines in common use, such as the dynamo and the motor. 



MAGNETIC FIELD AROUND A CURRENT- 

 BEARING WIRE 



Like a magnet, an electric current has 



lines of force. The iron filings show a 



cross section of the magnetic field. 



A SIMPLE ELECTROMAGNET 



A battery of electric cells, indicated by the 

 vertical lines at the top, supplies a current 

 of electricity. ^This current, in passing 

 through the coil of wire, makes a tem- 

 porary magnet of the bar of iron. 



