288 Peirce — Permeabilities and Reluctivities for Steel. 



Figure 8 shows the reluctivity of this steel for excitations 

 below #=100. 



Table VIII gives the results of an interesting study made 

 by Mr. Coulson of the magnetic properties of a piece of 

 Kidd's polished tool steel, for excitations between i7=250 

 and #=2500. 







Table VIII. 







H 



B 



/" 



E 



I 



300 



17470 



58-2 



0-017 



1364 



350 



17750 



50-7 



0-020 



1385 



400 



17980 



44-9 



0-022 



1399 



500 



18370 



36-7 



0-027 



1422 



600 



18710 



31-2 



0-032 



1441 



800 



19240 



24-0 



0-042 



1468 



1000 



19680 



19-7 



0-051 



1487 



1200 



20050 



16-7 



0-060 



1500 



1400 



20440 



14-6 



0-068 



1515 



1600 



20790 



13-0 



0-077 



1527 



2000 



21400 



10*1 



0-094 



1544 



2500 



22010 



8-8 



0-114 



1549 



The line obtained by plotting the reluctivity (R) against H 

 has only a very gentle curvature between these limits for this 

 annealed tool steel. 



I wish to express my obligations 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 measure- 

 ments recorded in this paper. 



The Jefferson Physical Laboratory, 



Harvard University, Cambridge, 



Mass. 



