170 HOW WE PRODUCE ELECTRICITY 



Are there many at the ends or in the middle ? Clean off the filings 

 and break the needle into two parts. Place these in the filings. 

 What happens? 



How the Magnetic Poles Act. These experiments show 

 us that not only do magnets attract certain metals, but 

 that if a magnet is cut in two parts, it will continue to be 

 magnetized. We notice that the greatest attractive force 

 is nearest the ends of the magnet. If we bring the north 

 pole of one magnet near the north pole of a suspended 

 magnet, the north pole of the latter moves away. If we 

 bring the south pole of a fixed magnet to the north pole of 

 a movable one, the south pole is drawn toward the north. 

 This always occurs when two magnets are brought to- 

 gether and gives a law which we may state as follows : 



Like magnetic poles always repel, and unlike magnetic 

 poles always altract each other. 



Demonstration 3. To Show the Magnetic Field. 



Place a bar magnet under a piece of white paper with a strip of 

 board of the same thickness on each side of it. Now shake iron 

 filings evenly over the paper. Tap the paper gently. Notice 

 what happens to the filings. Where are they most numerous? 

 How can you describe their arrangement on the paper? Make 

 a diagram of the magnet and of the lines of filings. How do they 

 compare with the illustration on page 171? 



A Magnet Influences Space around It. Tacks or iron 

 filings will jump across the air space to a strong magnet. 

 A compass needle will turn when several feet away from 

 a strong magnet. These facts indicate that the influ- 

 ence of the magnet extends in all directions from the mag- 

 net. This force decreases as the distance increases. The 

 space about the magnet in which this magnetic influence 

 exists is called a magnetic field. If a compass is placed in 

 a magnetic field, the needle will take the direction of the 

 lines of magnetic force. These lines are considered as 



