422 WELLS'S NATURAL PHILOSOPHY. 



Can the earth Magnetism may be also induced in a bar of 

 induce magnet- i^n bv the action of the earth. 



Most iron bars and rails, as the vertical bars 

 of windows, that have stood for a considerable time in a 

 perpendicular position, will be found to be magnetic. 



If we suspend a bar of soft iroa sufiBciently long in the air, it 

 ^u^j^ns"" '""of ^^^^ gradually become magnetic ; and although when it is first 

 magnetism in- suspended it points indifferently in any direction, it will at 

 earth? ^ * ^'^^^ point north and south. 



If a bar of iron, such as a kitchen poker, which has been 

 found to be devoid of magnetism, is placed with one end on the ground, 

 slightly inclined toward tho north, and then struck one smart blow with a 

 liammer upon the upper end it will acquire polarity, and exhibit tho attractive 

 and repellent properties of a magnet. 



Does magnetic Magnetic attraction can be made to exert 

 ten'd'"'th"rou?h ^^^ influcncc througli glass, paper, and solid 

 other bodies? ^^j^^ liquid substanccs generally which are not 

 capable of acquiring magnetic influence in the ordinary 

 manner. 



If a horse-shoe magnet be placed under- 

 FiG 352. neath a sheet of paper which has iron 



filings sprinkled over its surface, the fil- 

 ings, upon the approach of the magnet, 

 will arrange themselves in great regularity 

 in lines diverging from the poles of the 

 magnet, in^curves, and extending from 

 the one pole to the other, as is repre- 

 sented in Fig. 352. The numerous frag- 

 ments of iron, being rendered magnets by 

 induction, have their unlike poles fronting 

 each other, and they therefore attract one 

 another, and adhe'^e in the direction of their polarities, forming what are termed 

 magnetic curves. 



If a plate of iron is caused to intervene between the magnet and tho under 

 surface of the paper, the magnetic influence is almost entirely cut off. 



Do artificial "^94. Magucts, if left to themselves, gradu- 

 th^'ir'proper- ^^^Yi ^"^1 in a space of time varying with the 

 *'^^' hardness of tlio metal composing them, lose 



their magnetic properties, from the recombination of their 

 separate fluids. 



This is prevented by keeping their poles united by 



