CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



ON THE MAGNETIC BEHAVIOR OF HARDENED CAST 



IRON AND OF CERTAIN TOOL STEELS AT 



HIGH EXCITATIONS. 



By B. Osgood Peirce. 



Presented November 11, 1908. Received December 31, 1908. 



During the last few years the use of hardened cast iron for permanent 

 magnets has increased very much, and this material has proved especially 

 useful for such shapes as could not be easily forged from steel without 

 heating the metal red hot a number of times and thus making it mag- 

 netically unsatisfactory. Cast-iron magnets are very cheap, and they 

 may be made quite as strong and as permanent as magnets made of the 

 best tool steel, even if in strength, though not in permanence, they fall 

 a little behind magnets made of special "magnet steels." Moreover, 

 and this is sometimes of very great importance, the temperature coeffi- 

 cient x of a seasoned cast-iron magnet is usually much smaller than that 

 of a magnet of the same strength made of forged or formed steel. This 

 paper discusses briefly a number of determinations of the permeability 

 of specimens of fairly soft and of glass-hard cast iron of the same kind, 

 under excitations up to about 15,000 gausses, 2 and, for purposes of 

 comparison, considers also some measurements made upon hard and 

 soft Stubs " Polished Drill Rod " and upon hard and soft " Crescent 

 Polished Drill Rod." 



The principal apparatus used consisted of a yoke (Figure 1) which 

 weighed about 300 kilograms and was excited by a current (from a 

 storage battery) running through a set of amperemeters in series with 



1 Peirce, These Proceedings, 38 (1903) ; 40 (1905). 



2 Rowland, Phil. Mag., 46(1873); Fromme, Ann. d. Phys., 13 (1881); 33 

 (1888); Stefan, Ann. d. Phys., 38 (1889); H. E. J. G. DuBois, Ann. d. Phys., 

 31 (1888); 51 (1894); 13. Walter, Ann. d. Phys., 14 (1904); Ewing, Magnetic 

 Induction in Iron and other Metals ; DuBois, The Magnetic Circuit in Theory 

 and Practice. 



vol. xliv. — 23 



