CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY. 



THE DEMAGNETIZING FACTORS OF CYLINDRICAL RODS 

 IN HIGH, UNIFORM FIELDS. 



By B. Osgood Peirce. t 

 Presented by E. H. Hall, March 11, 1914. Received March 5, 1914. 



Any one who has been compelled to measure the permeability of 

 iron under high excitations, by experiments upon relatively short 

 rods exposed to strong magnetizing fields, must have had occasion to 

 notice that, under these circumstances, the corrections for the effects 

 of the self -demagnetizing forces are often very small. In the case of 

 an ellipsoidal specimen, it is possible to predict the phenomena which 

 one encounters in practice, 1 and although it is not easy to make long 

 ellipsoidal test rods with accuracy, there is a sufficiently close analogy 

 between the two cases to make the general conclusions reached for 

 ellipsoids applicable to the cylindrical rods usually employed in the 

 laboratory. 2 



It is well known that if an ellipsoid of soft, magnetizable material 

 and of fixed, constant susceptibility, k, were placed in a uniform 

 magnetic field, H, it would become uniformly magnetized by induction 

 and that the components of the field within it would be 



HJ ( 1 + 2irabcleKo) , HJ ( 1 + 2wabckL ) , H / ( 1 + 2rabckMo) , 



where a, b, c, are the lengths of the semiaxes, 



Ao = Jo (H-a) 3 /2. (.?+&) 1/2- (p+c)W (1) 



and Lq, Mo, have corresponding values. 



t Deceased January 14, 1914. 



iRayleigh, Phil. Mag., 22, 1886; Maxwell, Vol., II; Webster, Elect, and 

 Mag., §§ 192, 196; Peirce, N. P. F.; Yosida, Tokyo, Proc, 3, 8, 1906; Mallik, 

 Phil. Mag., 14, 1907; 15, 1908; Daniele, N. Cimento, 2, 6, 1911; H. E. J. G. 

 duBois, Deutsch. Phys. Gesell., Verh. 15, 8, 1913. 



2Ewing, Phil. Mag., 176, 1885; Tanakadate, Phil. Mag., 26, 1888; H. E. 

 J. G. duBois, Phil. Mag., 29, 1890. Wied. Ann., 46, 1892; Rossler, Elektro- 

 technische Zeitschrift, 14, 1893; Mann, Dissertation Berlin, 1895. Phys. 

 Rev., 3, 1896; Ascoli e Lori, Rendic. R. Acad. d. Lincei, 3: 2, 1894; 6: 2, 1897; 

 J. L. W. Gill, Phil. Mag., 46, 1898; Morin, Eel. Electr. 15, 1898; Holborn, 

 Sitzungsbericht d. Akad. Wiss. zu Berlin, 1, 1898; Benedicks, Wied. Ann., 6, 

 1901; Bihang Svenska V.-Akad. Handlinger, 27, 1902; H. E. J. G. duBois, 

 Wied. Ann., 7, 1902; Gumlich, Elektrotechnische Zeitschrift, 22, 1901; 30, 

 1909; Peirce, These Proceedings, 44, 1908; Am. Journal of Science, 28, 1909; 

 Shuddemagen, These Proceedings, 43, 1907; Peirce, Ibid., 49, 1913. 



