120 THE MAGNETIC CIRCUIT [ART. 41 



along ac is the same as that along bd, and secondly, the total 

 flux through cd is equal to that through ab. Or 



H.-ac-Hi-bd, 



and 



Dividing one equation by the other, and rearranging the terms, 

 eq. (58) is obtained. 



Prob. 22. Show that the total refraction which is in some cases 

 experienced by rays of light is impossible in the case of magnetic lines 

 of force. 



Prob. 23. Part of a flux emerges from the flank of a tooth into the 

 slot at an angle of 1 to the normal. What is the angle which the lines 

 of force make with the side of the slot in the iron, assuming the relative 

 permeability of the iron to be 1000? Ans. 90 - 0; = 3 17'. 



