476 MAGNETISM AND ELECTRICITY 



Bring pieces of copper, zinc, and other substances toward the 

 magnet. Do these affect it? Notice that the ends of the bar 

 magnet are marked. What can you state about the attraction or 

 repulsion of similar ends of magnets? Of opposite ends? Does 

 it make any difference in its effect on the suspended magnet 

 toward which end the nail is brought ? What substances do you 

 find attracted by the magnet? 



To the end of a small nail hanging by attraction to a magnet 

 bring another nail. How does the first nail act in respect to the 

 second ? 



Experiment 149. Suspend by a string a short bar magnet in a 

 sling, as in Experiment 148. Turn it around in several different 

 directions. After each change allow it to come to rest in whatever 

 position it will. Does it prefer any one position to all others? 



It was early discovered that when pieces of steel were 

 rubbed on a loadstone they took on the properties of the 

 loadstone and became magnets. In the experiments with 

 magnets, it was found that like poles repelled and unlike 

 poles attracted, and that iron or steel in contact with a 

 magnet becomes magnetized. Iron and steel are practi- 

 cally the only substances attracted by a magnet, although 

 nickel and cobalt and a few other substances have a 

 little attraction. Thus steel and iron are always used 

 for magnets. 



The Magnetic Field of Force. Experiment 150. Place a 

 plate of window glass about 8x10 inches above a bar magnet and 

 carefully sprinkle iron filings over it. Describe the behavior of the 

 filings. Sketch on a piece of paper their arrangement. Move a 

 small compass about above the glass plate and note the directions 

 the needle assumes. How do the actions of the needle and of the 

 filings compare? If feasible make a blue print of the filings. 



Holding the small compass two or three inches above the magnet 

 move it parallel with the magnet from end to end. Gently tap the 

 compass occasionally so that the needle will move freely. How does 



