CHAPTER XXIV 

 MAGNETS AND CURRENTS 



IN the twelfth century, there was introduced into Europe 

 from China a simple instrument which changed journeying on 

 the sea from uncertain wandering to a definite, safe voyage. 

 This instrument was the compass (Fig. 94), and because of the 

 property of the compass needle (a 

 magnet) to point unerringly north and 

 south, sailors were able to determine 

 directions on the sea and to steer for 

 the desired point. 



Since an electric current is practi- 

 cally equivalent to a magnet, it be- 

 comes necessary to know the most 

 important facts relative to magnets, 

 facts simple in themselves but of far- 

 reaching value and consequences in 

 electricity. Without a knowledge of 

 the magnetic characteristics of cur- 

 rents, the construction of the motor would have been impossible, 

 and trolley cars, electric fans, motor boats, and other equally 

 well-known electrical contrivances would be unknown. 



The attractive power of a magnet. The magnet best known 

 to us all is the compass needle, but for convenience we 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 carpet tacks, we find on lifting the magnet that 

 the tacks cling to the ends in abundance, but leave it almost 



225 



FIG. 04. The compass. 



