252 



MAGNETISM 



everywhere /x r The normal intensity N only has value over AC 

 where it is H x and over BD where it is H 2 , and the theorem 

 gives 



H x . AC - H 2 . BD = ^TTO-/^ 



or, since AC = AB cos X and BD = AB cos 2 anil AB =1, 



H x cos X - H 2 cos 2 ). 



o- = 



Bu 



cos = 





Ma - 



Hj r< H 2 



r /( 



- /q) H f c-o- H, 



