CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY, HARVARD UNIVERSITY, 



THE MAGNITUDE OF AN ERROR WHICH SOMETIMES 



AFFECTS THE RESULTS OF MAGNETIC TESTS 



UPON IRON AND STEEL RINGS. 



By B. Osgood Peirce. 



Presented May 11, 1910. Received May 20, 1910. 



The theory of the magnetic properties of a homogeneous ring of iron 

 or steel uniformly wound about by turns of insulated wire through 

 which a steady current of electricity can be made to pass, was first in- 

 vestigated by Kirchhoff, who showed that the intensity of the magnetic 

 field in the metal which thus forms the core of a ring solenoid, must 

 be inversely proportional to the distance from the axis of revolution 

 of the ring. He computed the mean value of the field in a ring of 

 rectangular cross section,^ and pointed out the advantages which rings 

 offer for measurements of the magnetic permeabilities of the metals of 

 which they are made. The next year, Stoletow, working under the 

 advice of Kirchhoff, took up the subject practically in the Physical 

 Laboratory of the University of Heidelberg and in 1872 published the 

 results of a long series of experiments upon a ring forged from a 

 wrought iron rod. In 187.3 appeared an account of the important 

 work of Rowland, begun three years before, on rings (toroids) of circu- 

 lar cross section, made of various kinds of iron and steel, and since 

 that time countless measurements of permeability have been made by 

 many observers ^ upon iron and steel rings; and when these rings 



^ Gustav Ivirchhoff, Pogg. Ann. Ergzbd. 5, 1 (1870). Gesammelte Ab- 

 handlungen, 22.3; A. Stoletow, Pogg. Ann. 146, 442 (1872); H. Rowland, 

 Phil. Mag. 46, 140 (1873); 48, ,321 (1874); C. Bauer, Wied. Ann. 11, .349 (1880). 



' J. A. Ewing, Magnetic Induction in Iron and other metals; G. vom 

 Hofe, Wied. Ann. 37, 482 (1889); H. Lehmann, Wied. Ann. 48, 406 (1893); 

 A. von Ettingshausen, Wied. Ann. 8, .5.54 (1879); H. du Bois, Magnctische 

 Kreise, 110 et seq. Berlin, 1894; L. Boltzmann, Anz. d. Wiener Akademie, 203 

 (1878); J. Sauter, Wied. Ann. 62, 85 (1897); L. Mues, Inaiig. Diss. Greif.swald 

 (1893); I. Schuetz, Journal f. Mathematik, 113, 161 (1894); Carl Neumann, 

 Ueber Ring Potentiale, Halle (1864). 



