FORCES ON MAGNETISED BODIES 265 



Hence the assumed system gives the same force on a whole body 

 as the system obtained by considering the imaginary surface layer 

 of magnetism. 



It is easy to show that the system of pressures and tensions in 

 air will account for the force on a straight wire carrying a current 

 C due to a field H at right angles to the wire or in the field due to 

 another parallel current. 



