202 Prof. A. Stoletow on the Magnetization* Functions 

 are connected by the relation 



3 + k 



The function p, he says, deserves the preference because, 

 " within a very large sphere of magnetizing forces, it possesses 

 a nearly constant value for all sorts of iron " {I. c. p. 435). The 

 values of p calculated by M. Riecke from his own and others'' 

 experiments do in fact accord very well; they give (p. 470) as 

 mean value for moderate decomposing forces the number 0*2372, 

 and as maximum value 



p = 0-2382. 



The purpose of the present note is to bring out that these 

 results are self-evident, and the above numbers have a very 

 simple meaning ; they are, namely, pretty close approximations 

 to the number 



%- =0-2387, 



which is obtained as the upper limit of p when we put k= go, 

 and consequently represents the ideal maximum of p. With 



1 . . 47T 



moderate decomposing forces j is always small compared with — 



(since ^here lies somewhere between 20 and 200*), and may, in 

 the first approximation, be neglected. On this account p remains 

 always nearly constant and independent of the quality of the ironf. 

 Indeed, for every other strongly magnetic material, about the 

 same value of p would result J. 



From this we see, on the one hand, that the numbers calcu- 

 lated by M. Riecke furnish a fair confirmation of the theoretical 

 consideration ; but, at the same time, we see that the quantity p 

 is very little suitable for characterizing the magnetizability of a 

 material, since for the sphere the influence of the quality of the 

 substance nearly vanishes before the influence of the form. It 

 can be proved that this holds good generally for every body the 



* For my iron ring the maximum of Jc was =174; with the kinds of iron 

 investigated by Mr. Rowland it was in nearly every case higher, and in one 

 case reached the value Jc=439 (ju =551-5). 



f A brief note in reference to this I find in Wiedemann's Galvanismus, 

 2nd ed. vol. ii. p. 403. 



% For a ring of annealed nickel Mr. Rowland found the maximum of 

 k=24 (/x = 305). According to this, even for nickel (at its maximum of 

 magnetizability) p may reach the value 02364. For steel the approxima- 

 tion to the absolute maximum - 2387 becomes still closer, and holds be- 

 tween wider limits of the decomposing force. 



