Magnetism 199 



iron while a magnet is held near the other end. The rod will 

 attract and hold part of the filings. 



Theory of Magnetism. It is believed that individual mole- 

 cules of any magnetic substance are always magnetized. In a bar 

 of iron that is not magnetized, the molecules are turned in all 

 directidns. In a bar that is magnetized, the molecules arrange 

 themselves so that their like poles lie in the same direction. 



Magnetic Field. The magnetic field may be illustrated 'by 

 sprinkling iron filings on a small plate of glass under which a 

 bar magnet has been placed. By tapping the glass, the filings will 

 arrange themselves in curved lines uniting the N and S poles of 

 the magnet, but some lines will pass out from the poles and fail 

 to unite with one another as 

 shown in the illustration. The 

 space around a magnet which is 

 influenced by its force is known 

 as its magnetic field. This field "x9^%?>-. ^-%%^\^^' 

 is strongest near the poles of *' I ' / j \\^;^:: :: ---- :: :^v''''/j: \ \ s 

 the magnet and becomes weaker \ t \\:^:^::::::^-'^y/ 

 as the distance from them in- ^^r/Xv-i'--''' 



creases. Each line is called a THE MAGNETIC FIELD 



line of force. Notice the lines of force. 



Experiment to Show Magnetic Fields. Place two bar 

 magnets in a straight line so that the N pole of one is a short 

 distance from the S pole of the other. Cover the magnets with a 



LINES OF FORCE FROM UNLIKE LINES OF FORCE FROM LIKE 



POLES OF Two MAGNETS POLES OF Two MAGNETS 



plate of glass and scatter iron filings on it. Tap the glass. Filings 

 will arrange themselves along lines of force from the two poles 

 mentioned. If one magnet is reversed so that the N poles of the 

 two magnets are near each other the filings will show that the 



