224: 



whence 



On Mirrors of Magnetism. 



u r v 



The well-known optical mirror formula for a spherical 



2 . 1 



mirror differs from this in having- instead of -. 



° r r 



In order that a magnetic image as at B in fig. 14 should 



be produced by a magnetic object at A, and with the relative 



strengths m 2 and m 1? not only must the reflecting surface pass 



through the point E such that 



AB m x 

 BE ~ m 2 ' 



but the curvature of the magnetic mirror is defined by the 

 condition previously laid down that 



AO_ m\ , 

 ttt\ — also. 

 \j\J m 2 



Now the optical mirror which will give at B the image of 

 A, and have its middle-point situated at E (as defined by the 

 former of these conditions) will not have for its centre. 



Fig. 16. 



In fact it will be a spherical surface having half the curvature 

 or twice the radius. If (fig. 16) the dotted circle FEGbe 



