CHAPTER III. 



THE MAGNETISM OF IRON. 



30. Ferromagnetism and electromagnetism. There are two 

 distinct groups of magnetic phenomena, namely, (a) the phe- 

 nomena of ferromagnetism, that is to say, the phenomena which 

 are associated with magnetized iron and steel, and (&) the phe- 

 nomena of electromagnetism, that is to say, the magnetic phe- 

 nomena which are exhibited by the electric current in the ab- 

 sence of iron and steel. In developing the subject of magnetism 

 it- is necessary to study ferromagnetism first because the phe- 

 nomena of ferromagnetism are much more familiar than the 

 phenomena of electromagnetism ; in fact, the phenomena of 

 electromagnetism are comparatively obscure, and, in many cases, 

 almost imperceptible, except when they are enhanced by the 

 presence of iron. Thus, a dynamo or an induction coil would 

 operate if all its iron parts were removed, but the effects pro- 

 duced would be so slight as to be almost imperceptible. Practi- 

 cally, therefore, the phenomena of ferromagnetism and the phe- 

 nomena of electromagnetism are inextricably associated with each 

 other. In the rational study of magnetism, however, a considera- 

 tion of the phenomena of the magnetism of iron leads to the all- 

 important conception of the magnetic field, and the subject of 

 electromagnetism is then developed on the basis of this concep- 

 tion as exemplified in Chapters IV, V, and VI. 



The magnet. The name magnet was originally applied to the 

 lodestone, a mineral composed of iron oxide, which, in its native 

 state, possesses the power of attracting iron. 



The electromagnet. One aspect of the magnetic effect of the 

 electric current, as described in Art. I and as shown in Fig. 2, is 

 that an iron rod which is wound with an insulated wire becomes 

 a magnet when an electric current is sent through the wire. 



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