

. ELECTRICAL MACHINERY 461 



or south pole (S). The mariners' and the engineers' 

 compasses work upon the same principle. 



604. Magnetic lines of force. Again, if a sheet of 

 paper be placed over a magnet and some filings then 

 dropped upon the paper, and if the paper is slightly 

 jarred, the filings will assume the position shown in 



Fig. 340. From this it is 

 gathered that the magnet 

 has lines of force and that 

 these lines are of the form, 

 indicated in Fig. 341. For 

 convenience it is assumed 

 FIG. 340 that the lines of force leave 



the magnet at the N pole and enter at the S pole. 



605. Laws of magnets. If the north and the south 

 poles of two magnets are determined and marked it will 

 be noticed that when one of the magnets is suspended so 

 it is free to move in any direction and the north pole of 

 the other is brought close to the south pole of the sus- 

 pended one, these two ends attract each other. If, on the 

 other hand, the N ends be brought together it will be 









FIG. 341 DIRECTIONS OF LINES OF FORCE 



noticed that they repel. Hence the general law of mag- 

 nets is deduced : Like poles repel and unlike poles attract. 

 The force of this attraction is found to vary inversely 

 as the square of the distance, i.e., increasing the distance 



