WHAT CAN MAGNETS DO? 



169 



How to Use a Compass. In the pocket compass the 

 needle is free to move over a disk on which the points of 

 the compass are printed. If the compass is put down flat, 

 the needle of the compass will move to and fro until it 

 finally points to the magnetic north. If now the disk of 

 the compass is shifted so that the N on the disk is just 

 under the needle, all compass directions will be shown 

 approximately correct. 



Demonstration 1. To Determine the Laws of Magnetic Poles. 



(a) Do both poles of a magnet attract magnetic substances? Bring 

 the north pole of a bar magnet into a pile of iron tacks. Test the 

 south pole in the same way. Test the center of the bar. Compare 

 results. Do both poles of the magnet attract a magnetic substance? 

 Does the equator of the magnet show strong attraction? 



(6) Relation of magnetic poles to each other. Suspend a bar magnet 

 vertically, N-pole down. Bring the south pole of a bar magnet near 

 the north pole of the suspended magnet. Bring the north pole of 

 the bar magnet near the north pole ; then near the south pole. 

 What are the results in each case? Make a statement concerning 

 the attraction and repulsion of magnetic poles. 



Demonstration 2. To Magnetize a Steel Sewing Needle. 



Drop the magnetized needle (p. 167) into iron filings on a sheet of paper. 

 Move the needle around and pick it up. Where do the filings cling? 



