PEIRCE. MAGNETIZATION IN IRON. 143 



values given as a result of experiments upon these beautiful test 

 pieces. 



If a series of observations be made by the Method of Reversals, 

 upon a piece of iron originally in a. neutral state, and if the permeabil- 

 ity and the susceptibility obtained in this way be plotted against the 



f 

 ~0 : : 7 



Figure 11 shows the results of observations made in the Jefferson Laboratory 

 upon a rod of Norway Iron. For excitations up to about 400, the specimen 

 was magnetized in a solenoid. For more intense fields, the determinations 

 were made by a modification of the Isthmus Method. 



intensity of the exciting field, those portions of the resulting curves 

 (Figure 7) which correspond to large values of E resemble hyperbolas 

 which have the x and the xj axes as asymptotes. A generation ago, 

 therefore, it seems to ha\'e occurred to a number of persons at about 

 the same time, that if the reciprocals of the permeal)ility and of the 

 susceptibility were plotted against E, the curves must become finally 

 more or less straight. It appeared upon trial that for values of R 

 larger than 100, say, the reluctance gives a line only slightly convex 

 upwards, and that the reciprocal of the susceptibility which for 

 comparatively weak fields has the general shape shown in Figure 8 

 becomes very nearly coincident wath a straight line drawn through 

 the origin under high excitation. This last function has been found 

 useful by Professor Kennelly in his paper upon the relation between 



