ON MAGNETIC PERMEABILITY, 1 AND THE MAXIMUM OF 

 MAGNETISM OF IRON, STEEL, AND NICKEL 



[Philosophical Magazine [4], XL VI, 140-159, 1873] 



More than three years ago I commenced the series of experiments 

 the results of which I now publish for the first time. Many of the 

 facts which I now give were obtained then; but, for satisfactory reasons, 

 they were not published at that time. The investigations were com- 

 menced with a view to determine the distribution of magnetism on 

 iron bars and steel magnets; but it was soon found that little could be 

 done without new experiments on the magnetic permeability of sub- 

 stances. 



Few observations have been made as yet for determining the mag- 

 netic permeability of iron, and none, I believe, of nickel and cobalt, in 

 absolute measure. The subject is important, because in all theories of 

 induced magnetism a quantity is introduced depending upon the mag- 

 netic properties of the substance, and without a knowledge of which 

 the problem is of little but theoretical interest; this quantity has 

 always been treated as a constant, although the experiments on the 

 maximum of magnetism show that it is a variable. However, the form 

 of the function has never been determined, except so far as we may 

 deduce it from the equation of Miiller, 



which, as will be shown, leads to wrong results. The quantities used 

 by different persons are as follows: 



, Neumann's coefficient, or magnetic susceptibility (Thomson). 



Tc, Poisson's coefficient. 



/*, coefficient of magnetization (Maxwell), or magnetic permeability 

 (Thomson). 



^-, introduced for convenience in the following paper. 



1 The word "permeability" has been proposed by Thomson, and has the same 

 meaning as "conductivity" as used by Faraday ('Papers on Electricity and Magnet- 

 ism,' Thomson, p. 484; Maxwell's 'Electricity and Magnetism,' vol. ii, p. 51.) 



