C. A. Perkins — Magnetic Permeability of Nickel. 229 



be increased on account of the heating of the ring. In one or 

 two cases where a strong current was used this effect was so 

 marked that a smaller value of 23 was found for the stronger 

 current than for the weaker, which could not be due simply to 

 the increase of the magnetic field. 



The latter part of the curves is a nearly straight line, and 

 when this is prolonged to cut the axis it gives the value which 

 23 approaches as a maximum for all magnetizing forces here 

 available. It is to be expected that the form of the curve will 

 change as it approaches the axis, to which it no doubt becomes 

 finally parallel, since p=l for non-magnetic bodies, and in no 

 known case is as low as zero. 



3oo - 



)X 200 



100 



1000 



3000 



5000 



7000 



23 



Such an inflection was observed in the curve for iron by 

 Eowland and by Fromme, as before stated. 



Faraday* also found that at very high temperatures nickel 

 still possessed the power of being attracted by his electro-mag- 

 net, so that it is doubtful whether the curve crosses the line 

 fi=l. 



But although 23 may never reach a maximum, yet the quan- 

 tity found by prolonging the curve to the axis gives the law of 

 the change of 23 with varying temperatures and is the highest 

 value of 23 that can be reached by ordinary magnetizing forces, 



* Exp. Res., vol. iii, p. 55. 



