8230 



7250 



6020 



48L0 



3300 



22° 



100° 



205° 



262° 



314° 



7820 



7180 



5950 



4740 



3820 



21° 



100° 



197° 



269° 



298° 



5860 



5S60 



5660 



5000 



3200 



-17° 



15° 



100° 



210° 



300° 



230 C. A. Perkins — Magnetic Permeability of Nickel. 



the metal becoming practically non-magnetic in this neighbor- 

 hood. 



The values thus found for these rings are given here : 



| temp., 

 ( temp., 



in i f - 



( temp., 



It will be seen that the values for rings I and II are as 

 nearly equal as can be determined by this method, and they 

 are therefore shown on the same curve where the values found 

 for ring I are indicated by the crossed circles. Those for ring 

 III vary somewhat less rapidly and lie constantly below the 

 others. 



This difference seems to belong to the metal itself, as it will 

 be seen on examination of the curves for the rings that /jl of 

 ring III goes down more rapidty than the others, though it 

 rises to the same height as ring I and higher than ring II at 

 the maximum point. 



If this curve be continued it must not be allowed to meet 

 the axis at a large angle, since this would indicate that the 

 ring resisted infinitely the passage of the lines of force, but it 

 must nearly coincide at the last part with the curve represent- 

 ing £>, the magnetizing force. 



This has been shown to be true by some observations made 

 by A. Becquerel. H. Becquerel* states that in some unpub- 

 lished experiments his father found that nickel is still slightly 

 magnetic when heated to about 600°, though only about 4 ^ 

 as much so as at ordinary temperatures. Faraday's observa- 

 tions indicate the same thing. 



The additional series made with ring I shows that the change 

 is continuous beyond the points indicated in the diagram. 



The tables given for ji and 23 include also the permeability 

 for temporary magnetism, the curves of which are drawn on 

 the same diagramf with the total permeability. (Fig. 1.) 



The permanent permeability may be readily found by sub- 

 tracting one of these from the other. 



These results are not nearly as regular as the others because 

 the temporary magnetism varies with many circumstances, 

 depending on the amount and direction of previous magnetiza- 

 tion and on the number of times the magnetism has been 

 reversed. 



If the ring has previously been strongly magnetized the first 

 few reversals cause a greater change of magnetism than the 

 subsequent, and the same is true for temporary magnetism. 

 * Ann. de Chimie et de Phys. f In broken lines. 



