CAPACITY OF CONCENTRIC SPHERES. 



76. An elliptical plate may be regarded as a very flattened 

 ellipsoid. We have then, at the limit, 



lira. ff\ = 



The density on the plate is expressed by 

 M i 



cr = 



I x 2 jy 2 



V l ~^~^ 2 



and it will be seen that the lines of equal density are concentric 

 and similarly placed ellipses. 



For a circular plate, we have simply, at a distance r from the 

 centre, 



M i M 



and the capacity of the plate is reduced to 





77. CONCENTRIC SPHERES. Let us suppose that a conducting 

 sphere is surrounded by a conductor, bounded by two spherical 

 surfaces concentric to the first. 



