410 MAGNETISM. 



bars may then be taken away, and the support slid 

 to its place. 



Magnetism is best communicated to compass- 

 needles by the following method. 



Procure a pair of magnetic bars, not less than 

 six inches in length. Fasten the needle down on 

 a board, and with a magnet in each hand, draw 

 them from the centre upon the needle outwards ; 

 then raise the bars to a considerable distance from 

 the needle, and bring them perpendicularly down 

 upon the centre, and draw them over again. This 

 operation repeated about twenty times will mag- 

 netize the needle, and its ends will point to the 

 poles contrary to those that touched them. 



In communicating magnetism, it is best to use 

 weak magnets first, and those that are stronger 

 afterwards ; but you must be very careful not to 

 use weak after strong magnets. 



A magnet loses nothing of its own power by 

 communicating to other substances, but is rather 

 improved thereby. 



Every kind of violent percussion weakens the 

 power of a magnet. A strong magnet has been en- 

 tirely deprived of its virtue, by receiving several 

 smart strokes of a hammer ; indeed, whatever de- 

 ranges or disturbs the internal pores of a magnet, 

 will injure its magnetic force. 



Fill a small dry glass tube with iron filings, press 

 them in rather close, and then touch the tube as if 

 it were a steel bar, and the tube will attract a light 

 needle; shake the tube, so that the situation of 

 the filings may be disturbed, and the magetic vir- 

 tue will vanish. 



Magnets should never be left with two north, or 

 two south poles together ; for when they are thus 



