Earth Shidy 839 



earth magnet lies near the North Pole of the earth. Thus, a magnet on 

 the earth's surface, if allowed to move freely, will turn its north pole 

 toward the south pole of the great earth magnet. Then, we might ask, 

 why not call the earth's magnetic pole that lies nearest our North Pole its 

 north magnetic pole ? That is merely a matter of convenience for us. We 

 see that the compass needle points north and south, and the arm of the 

 needle which points north we conveniently call its north pole. 



The above experiment with a suspended needle shows how the mariner's 

 compass is made. This most useful instrument is said to have been 

 invented by the Chinese, at least 1400 B. C, and perhaps even longer ago. 

 It was used by them to guide armies over the great plains, and the needle 

 was made of lodestone. The compass was introduced into Europe about 

 1300 A. D., and has been used by mariners ever since. To "box the com- 

 pass" is to tell all the points on the compass dial, and is an exercise which 

 the children will enjoy. 



We are able to tell the direction of the lines of force flowing from a 

 magnet, by placing fine iron filings on a pane of glass or a sheet of paper and 

 holding close beneath one or both poles of a magnet ; instantly the filings 

 assume certain lines. If the two ends of a horseshoe magnet are used, we 

 can see the direction of the lines of force that flow from one pole to the 

 other. It is supposed that these lines of magnetic force streaming from the 

 ends of the great earth magnet cause the Northern Lights, or Aurora 

 Borealis. 



Lodestone is a form of iron with a special chemical composition, and it is 

 a natural magnet. Most interesting stories are told of the way the ancients 

 discovered this apparently bewitched material, because it clung to the iron 

 ends of their staffs or pulled the iron nails from their shoes. In the Ward's 

 collection of minerals sent out to schools, which costs only one dollar, there is 

 included a piece of lodestone, which is of perennial interest to the 

 children. 



Magnets made from lodestone are called natural magnets. A bar 

 magnet or a horseshoe magnet has received its magnetism from some other 

 magnet or from electrical sources. An electro magnet is of soft iron, and is 

 only a magnet when under the influence of a coil of wire charged with 

 electricity. As soon as the current is shut off the iron immediately ceases 

 to be a magnet. 



LESSON CCXIX 



The Magnet 



Leading thought — Any substance that will attract iron is called a magnet, 

 and the force which enables it to attract iron is called magnetism. This 

 force resides chiefly at the ends of magnets, called the poles. The forces 

 residing at the opposite ends of a magnet act in opposite directions; in 

 two magnets the like poles repel and the unlike poles attract each other. 

 The needle of the mariner's compass points north and south, because the 

 earth is a great magnet which has its south pole as a magnet at the North 

 Pole of the world. 



Method — Cheap toy horseshoe magnets are sufficiently good for this 

 lesson, but the teacher should have a bar magnet, also a cheap toy compass, 

 and a specimen of lodestone, which can be procured from any dealer in 

 minerals. In addition, there should be nails, iron filings and tacks of both 

 iron and brass, pins, darning needles or knitting needles, pens, etc. Each 



