350 Peirce — Induction Coefficients of Hard Steel Magnets. 



limit had not been passed below which the induced moment 

 was proportional to the strength of the magnetizing field. The 

 induced moment was occasionally measured by balancing the 

 deflecting action of the induced magnetism by means of a 

 known current sent through a second small coil close to the 

 magnetometer needle. The rather complicated apparatus is 

 not shown in the diagram, for the method is not very con- 

 venient though it gives excellent results. 



A steel bar magnet could be tested in the same manner as 

 an unmagnetized bar, after the deflective effect of the perma- 

 nent magnetism had been balanced by the help of a suitable 

 steady current from the storage cell at the right of the diagram. 

 The permanent magnetic moments of the seasoned magnets 

 were determined on a long magnetometer bench in Gauss's 

 "A position." Observations were made by myself and by Mr. 

 C. G-. Persons on several hundred pieces of steel at various 

 stages on their way toward becoming seasoned magnets. The 

 induction coefficients and the magnetic moments, though they 

 were determined witli some accuracy, are given only approxi- 

 mately in the subjoined tables, and 1 believe that most of 

 them fairly represent what a second set»of similar magnets 

 would give. 



It is proper to say that some of the Crescent drill rod of 

 which I had a large quantity vv^as obtained directly from the 

 Crescent Steel Company of Pittsburg, but that much more 

 was purchased of different dealers at different times. The 

 Stubs and Jessops steels were also bought on various occasions 

 of different dealers, and I venture to hope that my specimens 

 fairly represent these steels. After testing large numbers of 

 magnets made of Crescent polished drill rod and of Jessops 

 round black tool steel I can only say that when hard these 

 steels seem to be magnetically indistinguishable, though 

 abnormal specimens occur. • The Jessops steel is cheaper than 

 the other but rougher and, as sold in the market, less thoroughly 

 annealed. A stont magnet made of Stubs polished drill rod 

 generally has a somewhat smaller permanent specific magnetic 

 moment than a similar magnet made of either Crescent drill 

 rod or of Jessops round tool steel, as appears from the 

 results recorded in Tables I and II. 



Table II represents observations made on a very large num- 

 ber of magnets. Each number in Table III, on the other hand, 

 is based on measurements of only two specimens, cut from one 

 of i^l sample rods very kindly furnished by the Crescent Steel 

 Company. Table lY records tests made upon four odd mag- 

 nets. 



In order to compare more exactly relatively stout magnets 

 made of Crescent drill rod, Stubs drill rod and Jessops 

 round tool steel, I procured of an instrument maker a large 

 number of hardened pieces of steel of each of these kinds, of 



