208 SCIENCE OF COMMON THINGS 



How iron bars become magnetic. Horse-shoe magnets. 



1937 Is iron under certain circumstances rendered magnetic by the 

 inductive action of tlie earth} s magnetism f 



Most iron bars and rails, as the vertical bars of win- 

 dows, that have stood for a considerable time in a per- 

 pendicular position, will be found to be magnetic. 



1938 If we suspend a bar of soft iron sufficiently long in the air, will it 

 assume magnetic properties ? 



It will gradually become magnetic; and although 

 5vlien it is first suspended it points indifferently in any 

 direction, it will at last point north and south. 



1939 How may a bar of iron, such as a kitchen poker, be made imme- 

 diately magnetic, without resorting to the use of other magnets f 



If the bar devoid of magnetism is placed with one 

 end on the ground, slightly inclined towards the north, 

 and then struck one smart blow with a hammer upon 

 the upper end, it will immediately acquire polarity, and 

 exhibit the attractive and repellant Droperties of a 

 magnet. 



1930 What is a horse-shoe magnet f 



It is a magnetic bar bent into the form of a horse-shoe. 



"When a piece of iron not magnetic is brought in 

 contact with a common magnet, it will be attracted 

 by either pole; but the most powerful attraction 

 takes place when both poles can be applied to the 

 surface of the piece of iron at once. The magnetic 

 bars are for this purpose bent into the shape of the 

 letter U, and are termed horse-shoe magnets. 

 Several of these are frequently joined together 

 with their similar poles in contact ; they then con- 

 stitute a magnetic battery, and are very powerful, 

 either for lifting weights, or charging other mag- 

 Fig. 93. nets. (See Fig. 93.) 



1931 If we break a magnet across the middle, what happens f 



Each fragment becomes converted into a perfect 

 magnet; the part which originally had a north pole 

 acquires a south pole at the fractured end, and the part 

 which originally had a south pole, gets a north pole. 



1933 If we divide up a magnet to the extreme degree of mechanical fine- 

 ness possible, will the pieces possess magnetic powers f 



Each fragment, however small, will be a perfect 

 magnet 



