MAGNETISM. 421 



Where dooB the '^^^- The magnetic power of an iron or steel 

 ™f'l!'body°Te-'^ magnet appears to reside wholly upon the sur- 

 "<ie? face, and to circulate about it. 



he^ Sered To rcudcr a bar of steel magnetic, the north 

 magnetic? p^jg q£ j^ niaguct is placcd on the center of a 

 bar of steel and repeatedly drawn over it toward one ex- 

 tremity ; the other half is subjected to a similar treat- 

 ment with the south pole of the magnet ; the bar is thu3 

 rendered magnetic, and only loses this property when 

 strongly heated. 



A bar of soft iron becomes magnetic by sim- 



Hoir is soft , , , 1 1 rv 



iron magnet- plc contact With a maguct, Dut tnc etiect, as 



before stated, is not permanent. 

 May iron be It is not ucccssary that absolute contact 



rendered map- iiii t i i r. 



netic by indue- should take placc between a bar of soft iron 



tioa? ^ . -, 1 . 



and a magnet, in order to render the iron 

 magnetic ; but whenever a magnet is brought near to a 

 piece of iron in any shape, the latter is rendered magnetic 

 by the influence of the former. To this phenomenon the 

 name of induction has been given, and the distance through 

 which this effect can take place is called the magnetic at- 

 mosphere. 



_,,„ ,,, Thus, let a bar of soft iron, B, as in Fig. 351, be 



brought near to a magnet, M, vrbose poles, north and 



"^ 1 south, are indicated by N and S. By induction, the 



' bar will be rendered magnetic, the end of the bar to- 



ward the north pole of the magnet constituting it3 



south pole, and the other end the north pole. 



In all cases, where either pole of a magnet is brought 



near to, or in contact with bodies capable of acquiring 

 AT magnetism, the part which is nearest to the pole of 



the magnet acquires a polarity opposite, while the re- 

 mote extremity becomes a pole of the same kind ; hence the attraction of a 

 magnet for iron, is simply the attraction of one pole of a magnet for the oppo- 

 site pole of another. 



How may the '^^'^ general effect of magnetization by induction may be 



phenomena of clearly exhibited by bringing a powerful magnet near to a 

 duction be ex- piecc of sofl iron, as a large key, when it will be found that 

 hibited f the large key will support several smaller ones ; but as soon 



as the body inducing the magnetic action is removed, they all drop ofll 



