Iron under Small Periodic Magnetizing Force*. 235 



If 01 = F, 0F = F r , FI = F„ it follows that 



F^/xH*. F r=i x r H a , F e =kF r w, 



where jju is what the permeability would be if there were no 

 eddy currents, 

 fx r is the observed apparent value of the permeability, 

 cl is the area of cross section of the rod. 

 co is the frequency multiplied by 2tt. 



and h is a constant. 



Then writing 6 for the angle FOI, the lag in phase of the- 



induction behind the magnetizing current. 

 C0 ^~F -^H«- 



^ 



and 



. n F e k~F r <» , 

 tan 6 = = — - — = Act). 

 h r 1 P 



In these equations co, fj, r , 6 are observed variable quan- 

 tities, while yb and k are constants for the specimen on the 

 assumptions given above, and these assumptions can be tested 

 by noting the agreement between the values of the quantities 

 found from the equations. 



