on Magnetic Testing. 3 



units, then diminished gradually from +9 C.G.s. units to 



— 9 c.G.s. units, and finally increased in like manner from 



— 9 c.G.s. units to +9 c.G.s. units, the intensity of magneti- 

 zation followed the curve A B C D E. 



Fiir. 1. 



It will be seen that the point E does not coincide with the 

 point A, and that the vertical distance of A above is 

 much greater than the vertical distance o£ C below 0. 



The specimen was now thoroughly demagnetized, and the 

 process repeated, when the curve A'B'C'D'E' was obtained. 

 It is important to notice that the point E' coincides with A'; 

 the curve is now closed. Further, an inspection of the 

 figure shows that the hysteresis loop is now symmetrical. 

 Cyclic alteration of the magnetizing force between limits 

 H=+9 c.G.s. units resulted in the curve being repeated 

 over and over again. 



A' is the true magnetization curve for the specimen in 

 the annealed condition ; it is this curve, and not the curve A, 

 that is characteristic of the magnetic properties of the material. 

 Table I., which is taken from the figure, shows how serious 

 are the errors involved in neglecting to render the specimen 

 neutral before proceeding to carry out the tests. It will be 



B 2 



