134 FIRST YEAR COURSE IN GENERAL SCIENCE 



through a wire is to wind the wire from north to 

 south around a magnetic compass. If no current is pass- 

 ing, the needle will keep its north and south position just 

 as if no wire were present; but if a current passes through 

 the wire, it causes the needle to turn from its north-south 

 position toward the east or west, according to the direction 

 of the current above the needle. 



144. Magnetism. The power to attract pieces of iron 

 or steel (which is a form of iron) is called magnetism. Bodies 

 having this property are magnets. Iron and steel are more 

 strongly magnetic than any other metals. If a light piece of 

 iron is placed near a magnet, it 

 moves to the magnet and clings to 

 it; but if the magnet is the lighter 

 of the two bodies, it moves toward 

 the piece of iron. 



Not all pieces of iron are magnets, 

 but the property of magnetism may 

 MAGNETIC always be given to iron. This may 

 be done by striking an iron bar while 

 it is held in a north-south position, or 

 by rubbing the iron with a magnet. 

 In either of these cases, a bar of iron 

 becomes a temporary magnet, but a 



of iron to the east of either steel bar retains its magnetism and 

 becomes a permanent magnet. 



There is an ore of iron called 

 magnetite that is naturally magnetic; it does not have 

 to be magnetized. It is found in veins in rocks. 



The needle in a compass is a slender piece of magnetized 

 steel which, if balanced on a pivot, will swing from any other 

 position until it lies in a north and south direction. It is 

 upon such an instrument that the pilot of a ship or a surveyor 

 depends to determine the points of the compass when the 

 sun or stars are hidden. 



FIG. 68. A 



NEEDLE 



The needle is free to 

 move around a pivot upon 

 which it is supported. 1. It 

 is at rest, pointing north 



end? 2. Would a copper 

 rod produce the same effect? 



