334 Mr. H. A. Rowland on the Magnetic Permeability 



as this. Hence we may take as the provisional value of the 

 maximum of magnetization of cobalt in round numbers 3 = 8000, 

 or 23 = 100,000. 



We also see from Table IV. that, at least in this case, the per- 

 meability of cobalt is less than that of nickel, though we could 

 without doubt select specimens of cobalt which should have this 

 quality higher than a given specimen of nickel. The formula 

 at the foot of the Table also shows, by the increased value of 

 the coefficient of k in the right-hand member, that the diameter 

 of the curve is much less inclined to the axis of 3 in this case 

 than in the case of nickel or iron. In this respect the three 

 metals at present stand in the following order — cobalt, nickel, 

 iron. This is the inverse order also of their permeability ; but 

 at present I have not found any law connecting these two, and 

 doubt if any exact relation exists, though as a general rule the 

 value of the constant is greater in those curves where the per- 

 meability is least. 



In a short abstract in the ' Telegraphic Journal/ April 1, 

 1874, of a memoir by M. Stefan, it is stated " that the resist- 

 ance of iron and nickel to magnetization is at first very great, 

 then decreases to a minimum value, which is reached when the 

 induced magnetic moment is become a third of its maximum." 

 This will do for a very rough approximation, but is not accu- 

 rate, as will be seen from the following Table of this ratio from 

 my own experiments : — 



Experiments published in August 1873. 



Iron. 



Tables I. 



and. II. 



1 

 3-02 



Iron. 

 Table III. 



Bessemer 



steel. 

 Table IV. 



Iron. 

 Table V. 



Nickel. 

 Table VI. 



1 

 2^64 



1 

 265 



1 

 2-68 



1 

 315 



Steel. 

 Table VII. 



1 

 2-46 



I 



Experiments of present paper. 



Nickel. 

 Tables I. and II. 



Nickel. 

 Table III. 



Cobalt. 

 Tables IV. and V. 



1 

 3-23 



1 



3-14 



1 

 4-2 



The average of these is, if we include Bessemer steel with the 

 iron, as it is more iron than steel : — 



Iron, ^r 5 = Yl » Nickel > 



Cobalt,^ 



