198 Our Surroundings 



the course of ships on the ocean. The compass was the first 

 practical use made of the power of magnetism. 



The compass consists of a magnetized steel needle balanced 

 to rotate horizontally over a round disc. This disc is marked 

 in degrees and usually has the directions north, northeast, east, 

 southeast, south, southwest, west, and northwest indicated upon it. 

 The needle and disc are set in a brass frame having a glass top. 



The usefulness of the compass lies in the fact that the needle 

 tends always to point nearly north and south. The true north is 

 determined by the observation of the sun at noon and of the 

 North Star at night. It is thought that the first compass was 

 made of lodestone. The name lodestone, in fact, was given mag- 

 netic ore because the word lode means path, or way, hence some- 

 thing that directs or leads. 



Brass and glass are used in making a compass because they 

 do not interfere with the magnetic influence of the earth. A 

 compass box of steel or iron would destroy the magnetic power 

 of the needle. 



You can illustrate the principle of the compass in a simple 

 way. Balance on a small cork a piece of steel wire about eight 

 inches long and float it on water in a glass dish. Notice that 

 the wire does not assume any definite direction. Magnetize the 

 wire and again float it on the cork in the water and observe 

 whether it assumes any particular direction. It will point nearly 

 north and south. 



J Induced Magnetism. 



, Induced magnetism is a term 



s used for what occurs when a 



N S piece of iron touches a magnet. 



tf The iron becomes a magnet. 



You can illustrate this by sus- 

 INDUCED MAGNETISM pending a tack from a bar 



Each tack becomes a temporary magnet. magnet) a seC Ond tack from 



the first tack, and so on. Remove the first tack from the magnet 

 and notice what occurs. The magnetism which the tacks showed 

 is induced magnetism. This may occur without contact, as may 

 be shown by placing iron filings near one end of a short rod of soft 



