LESSONS IN PHYSICS. 91 



Magnetism. A magnet is a body which has the property of at- 

 tracting iron, and when suspended, so as to turn freely, of assum- 

 ing a north and south direction. The end toward the north is 

 called the north pole of the magnet, while the other end is called 

 the south pole. An ore of iron, called magnetite or lodestone, is 

 found in many localities. Lodestone was known to the ancients, 

 being found in Asia Minor, in Sweden, in the region of Lake Super- 

 ior, and in many other localities. The name lodestone or leadstone 

 seems to have been derived from the Saxon laedan,to lead. When 

 a steel bar or needle is rubbed by a natural magnet, it acquires 

 magnetic qualities and becomes an artificial magnet. Artificial 

 magnets are more powerful and convenient than lodestone mag- 

 nets, and are the only ones in ordinary use. 



Magnets maybe straight, when they are bar magnets; or they 

 may be in the shape of a letter U, when they are called horseshoe 

 magnets. A bar of soft iron, called an armature, laid across the 

 poles of a magnet enables it to retain its magnetism for a longer 

 time. In the case of bar magnets they are laid in pairs, an arm- 

 ature connecting the north pole of one with the south pole of the 

 other. 



If a magnet is rolled in a mass of fine iron filings, it will be 

 seen that the attractive force is stronger at the ends, gradually 

 diminishing to zero at the center. If a bar magnet, as an ordinary 

 knitting needle, is broken at the zero point, each end instantly 

 becomes a complete magnet, with strong poles and zero center 

 as before, and the same will be true however short the pieces be- 

 come. Either pole of the magnet attracts iron, but if we experi- 

 ment with two magnets, one of which is suspended, we find that 

 the north pole of one attracts the south pole of the other, but 

 repels the north pole, and vice versa; that is, poles of the same 

 name repel each other, while poles of different names attract 

 each other. The iron or steel attracted by a magnet becomes 

 itself a magnet, has a north and south pole, is polarized, and in 

 turn may polarize other pieces of iron or steel, as is shown by 

 the experiment of rolling the magnet in iron filings. If a piece 

 of writing paper is laid over a strong magnet, and then fine iron 



