306 POLARITY AND INDUCTION. SECT. XXX. 



turbed. Another property of a magnet is the attraction 

 of uninagnetized iron. Both poles of a magnet attract 

 iron, which in return attracts either pole of the magnet 

 with an equal and contrary force. The magnetic in- 

 tensity is most powerful at the poles, as may easily be 

 seen by dipping the magnet into iron filings, which will 

 adhere abundantly to each pole, while scarcely any 

 attach themselves to the intermediate parts. The 

 action of the magnet on unmagnetized iron is confined 

 to attraction, whereas the reciprocal agency of magnets 

 is characterized by a repulsive as well as an attractive 

 force, for a north pole repels.a north pole, and a south 

 repels a south pole. But a north and a south pole 

 mutually attract one another, which proves that there 

 are two distinct kinds of magnetic forces, directly op- 

 posite in their effects, though similar in their mode of 

 action. 



Induction is the power which a magnet possesses of 

 exciting temporary or permanent magnetism in such 

 bodies in its vicinity as are capable of receiving it. By 

 this property the mere approach of a magnet renders 

 iron or steel magnetic, the more powerfully the less the 

 distance. When the north pole of a magnet is brought 

 near to, and in the line with, an unmagnetized iron bar, 

 the bar acquires all the properties of a perfect magnet; 

 the end next the north pole of the magnet becomes a 

 south pole, while the remote end becomes a north pole. 

 Exactly the reverse takes place when the south pole is 

 presented to the bar ; so that each pole of a magnet 

 induces the opposite polarity in the adjacent end of the 

 bar, and the same polarity in the remote extremity ; 

 consequently the nearest extremity of the bar is at- 

 tracted, and the farther repelled ; but as the action is 

 greater on the adjacent than on the distant part, the 

 resulting force is that of attraction. By induction, the 

 iron bar not only acquires polarity, but the power of 

 inducing magnetism in a third body ; and although all 

 these properties vanish from the iron as soon as the 

 magnet is removed, a lasting increase of intensity is 

 generally imparted to the magnet itself by the reaction 

 of the temporary magnetism of the iron. -Iron acquires 

 magnetism more rapidly than steel, yet it loses it us 



