146 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Figures 11, 12 and 13 reproduce the results of a series of meas- 

 urements made two or three years ago in the Jefferson Laboratory 

 upon specimens of Bessemer steel and of Norway Iron. For excita- 

 tions up to about 400 the specimens were magnetized in a slender 

 solenoid about five meters long, but for stronger fields a modification 

 of the Isthmus Method was employed. Figure 14 shows some 

 measurements made lately upon a specimen of American Ingot 

 Iron magnetized in the shorter solenoid described above. Such 

 curves become practically straight for much weaker fields in the 

 case of some kons than in others. 



I wish to express my great obligation to the Trustees of the Bache 

 Fund of the National Academy of Sciences for the loan of some of 

 the apparatus used in making the observations mentioned in this 

 paper. 



The Jepfersox Physical Laboratory, 

 Cambridge, Mass. 



