CHAPTER IX. 



PROPERTIES OF DIELECTRICS AND MAGNETIZABLE BODIES. 



178. Magnetic Phenomena. In the previous treatment 

 of electrostatics we have supposed all of space not occupied by 

 conductors to be filled with a single uniform dielectric. In this 

 chapter we shall remove this restriction and consider the distribu- 

 tion of the forces when any number of varying media are present 

 besides the conductors. Inasmuch as all the phenomena here 

 treated have exact analogues in the phenomena of magnetism, we 

 shall first briefly describe magnetic phenomena. A magnet is 

 a piece of loadstone, or of metal, generally iron or steel, possessing 

 the property of attracting iron, and of attracting or repelling 

 other magnets. The forces thus developed are called magnetic 

 forces. A small magnet in the form of a filament or needle, under 

 the action of any other magnet, tends to set itself in a certain 

 direction at every point in space, and this direction is said to be 

 the direction of the magnetic force at the point. A portion of 

 space in which such forces are exerted on the magnetic needle 

 is called a field of magnetic force, and may be represented by 

 drawing lines of force in every portion of it. If the lines of force 

 are straight and parallel, the field is said to be straight or uniform. 

 Different parts of a magnet possess opposite properties with 

 regard to attraction or repulsion, we may therefore consider them 

 charged with matter of different signs. We make use of the term 

 matter here precisely" as in connection with electricity, not to 

 denote something which has inertia, but simply something which 

 attracts, and which is measured by its power of attraction. Experi- 

 ment shows that any magnet placed in a uniform field experiences 

 no resultant force, but only a couple. We therefore conclude 



