2 go SCIENCE OF HOME AND COMMUNITY 



position. The power of a magnet to take this position was 

 not known till the end of the eleventh century, and then only 

 to a few learned men. They did not think it safe to tell the 

 common people about its use in steering ships, for fear they 

 would be considered magicians, so it was a long time after, 

 probably over a hundred years, before the compass was in 

 common use. 



The tendency of the compass to point north and south is 

 explained by saying that the whole earth acts like a huge 

 magnet with its two magnetic poles near the geographic poles. 

 The compass points to the magnetic north pole and not to 

 the geographic north, so that for most sections of the earth a 

 certain number of degrees must be added to or subtracted 

 from the reading of the compass, to get the true north. As 

 one passes east or west these corrections vary. Since in re- 

 cent years so much steel has been used in the construction 

 of steamships, it is found that the compass is influenced 

 by the mass of iron near it. For these two reasons, 

 therefore, some substitute for the compass in guiding ships 

 has been sought. 



LABORATORY EXERCISE 28 



Purpose. To study the action of the compass. 



Apparatus. Compass, two darning needles, knitting needle, 

 cork, magnet. 



Directions, i. Magnetize a knitting needle by rubbing an 

 end of the needle on one end of the magnet, and the other end 

 of the needle on the other end of the magnet. Fold a piece of 

 paper about one inch square, diagonally. Place the needle 

 at its middle in the crease of paper and suspend the paper by 

 means of a fine thread. In what position does the needle come 

 to rest? Compare with the compass. Move the needle and 

 try several times. Does it always come to rest in the same 

 position ? 



2. Magnetize a large darning needle by rubbing the point on 

 the north pole of a magnet and the eye end on the south pole. 



