MAGNETISM 197 



the position that a compass needle would in the same situa- 

 tion. These invisible lines of force explain how a magnetic 

 body may affect another without being brought into actual 

 contact with it. As would be expected, the further apart 

 such bodies are, the less will be the effect. When a body not 

 naturally a magnet is given magnetic properties by contact 

 with a magnet, it is said to be magnetized by induction. 



Practical Exercises 



1. Carefully place a sewing needle on the surface of a basin of water. 

 Does it come to rest in any definite position? Make three trials. 



2. Gradually bring one end of a bar magnet toward the needle. How 

 does the latter behave? 



3. Present the other end of the magnet to the needle. What result? 



4. Magnetize the needle just used by stroking it several times in one 

 direction with one end of the bar magnet. Place on the surface of a 

 basin of water at some distance from any iron. In what position does 

 the needle now come to rest? (Make several trials.) 



5. Repeat experiments 2 and 3 with this needle. What is the result? 



6. Slowly bring the north pole of a bar magnet toward the north pole 

 of a compass. What is the result? 



7. Repeat the foregoing experiment with the south pole of the magnet. 

 Can magnets repel as well as attract? 



8. Do like or unlike poles attract? 



9. If we call the end of the magnet which points to the north the 

 north pole, is the north magnetic pole a north or a south pole? 



