MAGNETISM 



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10. Ship's magnetism.— A ship while in the process of being con- 

 structed will acquire magnetism of a permanent nature under the 

 extensive hammering it receives in the earth's magnetic field. After 

 launching, the ship will lose some of this original magnetism as a 

 result of vibration, pounding, etc., in varying magnetic fields, and will 

 eventually reach a more or less stable magnetic condition. This mag- 

 netism which remains is the so-called 'permanent magnetism of the 

 ship. 



Blue 









Figure 3. — Terrestrial magnetism. 



11. The fact that a ship has permanent magnetism does not, of 

 course, mean that it cannot also acquire induced magnetism, when 

 placed in a magnetic field such as the earth's field. The amount of 

 magnetism induced in any given piece of soft iron is dependent upon 

 the field intensity, the alignment of the soft iron in that field, and 

 the physical properties and dimensions of the iron. This induced 

 magnetism may add to or subtract from the permanent magnetism 



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