and Maximum of Magnetism of Nickel and Cobalt. 339 



(3) The curve showing the relation between the magnetiza- 

 tion and the magnetic permeability, or Neumann's coefficient, is 

 of such a form that a diameter can be drawn bisecting chords 

 parallel to the axis of 53, and is of very nearly the form given by 

 the equation 



■n . % + bfi + w 

 fi= B sin ^- j 



where B, b, and ~D are constants, //, is the ratio of the magneti- 

 zation to the magnetizing-force in an infinitely long bar, and 53 

 is the amount of magnetization. 



(4) If a metal is permanently magnetized, its resistance to 

 change of magnetism is greater for low magnetizing-powers than 

 when it is in the normal state, but is the same for high magne- 

 tizing-powers. This applies to the permanent state finally 

 attained after several reversals of magnetizing-force ; but if we 

 strongly magnetize a bar in one direction and then afterwards 

 apply a weak magnetizing-force in the opposite direction, the 

 change of magnetization will be very great. 



(5) The resistances of nickel and cobalt to magnetization vary 

 with the temperature; but whether it is increased or not in 

 nickel depends upon the amount of magnetization : for a mode- 

 rate amount of magnetization it decreases with rise of tempera- 

 ture very rapidly ; but if the magnetization is high the resistance 

 is increased. In cobalt it apparently always decreased, whatever 

 the magnetization. The resistance of iron to magnetization is 

 not much affected by the temperature. 



(6) The resistance of any specimen of metal to magnetization 

 depends on the kind of metal, on the quality of the metal, on the 

 amount of permanent magnetization, on the temperature, and on 

 the total amount of magnetization, and, in at least iron and 

 nickel, decreases very much on careful annealing. The maxi- 

 mum of magnetization depends on the kind of metal and on the 

 temperature. 



(7) Iron, nickel, and cobalt all probably have a maximum of 

 magnetization, though its existence can never be entirely estab- 

 lished by experiment, and must always be a matter of inference ; 

 but if one exists, the values must be nearly as follows at ordinary 

 temperatures. Iron when 53 = 175,000 or when 3 = 139,000; 

 nickel when 53 = 63,400 or when 3 = 4910; cobalt when 53 = 

 100,000(?) or when 3 = 8000 (?). 



(8) The maximum of magnetization of iron and nickel de- 

 creases with rise of temperature, at least between 10° C. and 

 220° C, the first very slowly and the second very rapidly. At 

 220° C. the maximum for iron is when 95 = 172,000 and 

 3 = 13,600, and for nickel when 53 = 49,000 and 3 = 3800. 



Z2 



