THE EXTENT OF MAGNETIC ATTRACTION 



329 



FIG. 222. A magnet. 



we will use a magnetic needle in the shape of a bar larger 

 and stronger than that employed in the compass. If we 

 lay such a magnet on a pile of iron filings, it will be found 

 on lifting the magnet that the filings cling to the ends in 

 tufts, but leave it almost bare in the center (Fig. 222). The 

 points of attraction at 

 the two ends are called 

 the poles of the mag- 

 net. 



If a delicately made 

 magnet is suspended 

 as in Figure 223, and 

 is allowed to swing 

 freely, it will always 

 assume a definite north 

 and south position. The pole which points north when the 

 needle is suspended is called the north pole and is marked 

 N t while the pole which points south when the needle is 

 suspended is called the south pole and is marked S. 



A freely suspended magnet points nearly north and south. 

 A magnet has two main points of attraction 

 called respectively the north and south poles. 



306. The Extent of Magnetic Attraction. If 

 a thin sheet of paper or cardboard is laid over a 

 strong, bar-shaped magnet and iron filings are 

 FIG. 223. -The then gently strewn on the paper, the filings 

 clearly indicate the position of the magnet be- 

 neath, and if the cardboard is gently tapped, the 

 filings arrange themselves as shown in Figure 224. If the 

 paper is held some distance above the magnet, the influence 

 on the filings is less definite, and finally, if the paper is held 

 very far away, the filings do not respond at all, but lie on 

 the cardboard as dropped. 



rn H n 

 needle. 



