26 



THE MAGNETIC CIRCUIT 



[ART. 13 



QN being a tangent to the saturation curve at the point N under 

 consideration. An objection to this definition is that according to it 

 the per cent saturation does not approach 100 as N increases 

 indefinitely; on the contrary, the per cent saturation gradually 

 decreases to zero beyond a certain value of N. This is, of course, 

 absurd. Moreover, the foregoing definition of the Institute refers 

 explicitly to the " percentage of saturation of a machine," and it 

 is not clear whether magnetization curves of the separate materials 

 are included in it or not. The practical advantage of this definition 

 as compared to that given above is that it is not necessary to 

 know the value of B 8 . 



FIG. 4. A magnetization curve analyzed. 



13. Problems Involving the Use of Magnetization Curves. 

 The following problems have been devised to give the reader a clear 

 understanding of the meaning of magnetization curves, and to 

 develop fluency in their use. These problems lead up to the 

 magnetic circuit of electric machines treated in Chapters V and 

 VI. With almost any arrangement of a magnetic circuit there 

 is some leakage or spreading of the lines of force, which is difficult 

 to take into account theoretically. This leakage is neglected in 

 most of the problems that follow, so that the results are only 

 approximately correct. Leakage is considered more in detail in 

 Art. 40 below, though practical designers are usually satisfied with 



