244 MAGNETISM 



The component parallel to the surface is 



4 

 H sin 7; TT! sin 0. 



7 



Thus the condition for continuity of potential is satisfied. 

 The normal intensity just outside the surface is 



H cos + | TT! cos 



and as the medium is air this is equal to the normal induction. 

 The normal intensity just inside the surface is 



H cos - TT! cos 

 o 



and since the permeability is JUL the normal induction is 



cos 6- ITT! cos 



Equating the normal induction without and within, the condition 

 of continuity of flux of induction is satisfied by 



whence I = " - - H. 



47T/X + 2 



The intensity of field within the sphere is 



If /A is large, as it may be for iron when H is not very small, 

 this approaches the value 



3H 

 M 

 while I approaches the value 



3H 



47T 



or approaches the same value for all large values of /j.. The 



Q 



normal intensity j ust outside the sphere (H + o?rl) cos approaches 



the value 



3H cos 



and the tangential intensity (H ^7rl)sin 6 approaches zero unless 



